Smart logging technologies have been increasingly applied to petroleum companies with the digital and intelligent advancement. Especially remote skills emerge as the times require to resolve difficulties in conventional logging, such as long well occupation time, big logging costs, low efficiency and high labor intensity. Remote control of logging equipment can be attained by means of wireless transmission, so that experts as well as technical and safety personnel can examine and analyze data, and regulate parameters to guarantee all logging operation in high quality, efficiency and safety. Results show that (i) the established new remote control system is well applicable to logging operation; (ii) its application acquires real-time monitoring and transferring logging curves from numerous wells, solves on-site abnormalities in time, reduces well occupation time and logging costs, and optimizes human resources; and (iii) promoting this system is of guiding significance for next breakthrough made in core online logging technologies, and collaborative innovation across well areas and departments.

Normal-pressure gas reservoirs in Dingshan block along the margin of Sichuan Basin are confronted with technical challenges, i.e., low fracture-induced complexity giving rise to shortage of fracture-conditioned reserves, inconvenient post-fracturing drainage creating slow productivity release, and small recoverable reserves and difficult benefit development. With three objectives of addressing these challenges, such as the adequate reserve control in stimulation areas, and the reduction of both drainage load and stimulation cost, an efficient stimulation process with low cost, which the extreme limited-entry perforation to promote equilibrium and the integrated fracturing and drainage for composite load reduction are conducted as the dominant measures, and the simple formula of "drag reducer + cleanup additive" is used for cost reduction, has been developed for the normal-pressure shale gas in this block. Results show that (i) the extreme perforation can ensure the uniform initiation of fracture clusters, enhance the coverage rate from 75% to 90% in single-stage fracturing, and make the stimulated reservoir volume (SRV) by 15% higher than before; (ii) the drainage load is released through the composite load reduction, and the intensity of both fracturing fluid and proppant is optimized to be 15-20 m³/m and 1.5-2.0 m³/m, respectively. The rapid startup and drainage after fracturing without shut-in, running tubing during the initial fracturing, and gas lift cleanup can release the productivity while SRV assurance; and (iii) the fracturing-fluid system with low damage and cost can cut down the cost under such stimulation. Practice has proven that, after the application of this new low-cost fracturing technology to normal-pressure gas reservoirs by 6 well times from 2022 to 2023, the stimulation effect is improved by 60.2% and the fracturing cost reduced by 15.3%, respectively, which may provide successful experience for the subsequent large-scale benefit development in the low-grade reservoirs with normal pressure.

Completion-fluid density is essential for borehole stability in deep marine openhole horizontal wells with the horizontal length over 2,000 m due to long cycle time and complex string structure highly needed for the stability whose relation to both trajectory azimuth and borehole inclination should be taken into account. Therefore, the influence of producing pressure differences on the stability was analyzed for those wells with or without fractures through numerical simulation and two Drucker-Prager criteria to estimate both strength failure and effective plastic strain. In addition, one method for density evaluation was created for stability assurance. Results show that (i) there exists the best stability in some horizontal wells without fractures along the direction of maximum principal stress, and this stability is increased with the increased inclination; and (ii) there exists the most stable wells in the others with fractures whose dip of 90° goes the maximum principal stress. The fracture strike that moves to the direction of the stress from that of minimum stress makes the stability somehow better. And this borehole stability grows with the increased dip. In fact, this method has been applied to Pz3-4D well successfully to verifying simulation ending, which may provide a novel solution for stability improvement in deep openhole horizontal wells.

Most deep coalbed methane (CBM) horizontal wells in Nalinhe area are confronted with difficult trajectory control and low drilling rate in effective reservoirs. Therefore, taken JA-31NH6 well as an example, some key drilling technologies which include the multi-factor to optimize well location, the multi-marker to condition targeting, and the multi-means for precise steering were studied from drilling engineering, well logging, mud logging and 3D seismic exploration. Results show that (i) the micro-amplitude structure is exactly characterized through 3D seismic combined with trend structure, and the well location is optimized on the basis of CBM thickness, maturity, and roof and floor lithology; (ii) the deviation is fine-tuned for targeting in accordance with 6 marker beds represented by Maoergou limestone; (iii) both vertical profile of lithological combination and parameter tables of each lithology are established by making full use of drilling, well-logging and mud-logging data, especially near-bit azimuth gamma and elemental mud logging. And accurately, the drilled lithology can be analyzed, the bit position can be traced, and the horizontal section can be steered; and (iv) the CBM thickness, micro-amplitude structure, and wellbore trajectory and quality as a whole should be taken into consideration during drilling the horizontal section in an effort to improve the development effect by integrating geology with seismic engineering together with fine trajectory adjustment. As a result, the drilling rate is increased from 50.7% to 91.6%, which achieves the scientific, efficient, optimal and fast drilling in deep CBM horizontal wells in this area. These drilling technologies may provide reference for such deep CBM horizontal wells in other areas.

Some renewable tail gas with rich water may enlarge burner's operating load during natural-gas dehydration and tail gas treatment, and even lead to frequent troubles in this burner. Therefore, a two-stage method which the shell-tube heat exchanger is conducted as the heat recovery device and the finned heat exchanger as the forced cooling device has been proposed to separate cooling vapor. Its separation mechanisms were analyzed for the vapor in the renewable tail gas, and the separation effect of two-stage cooling was discussed through simulation calculation as well. In addition, the system of tail gas treatment was optimized for Xiangguosi underground gas storage (UGS) based on calculation results, and its operation were compared with simulation. Results show that (i) cooling the renewable tail gas under constant pressure can improve the condensation separation rate; (ii) the proposed method makes as little gas enter into an incinerator as possible to reduce the troubles through lightening the load; and (iii) with heat recovery, the optimized treatment system reduces not only energy consumption in the incinerator but carbon emission. In conclusion, this two-stage vapor separation method can realize the renewable tail gas in deep dehydration to further de-load in the burner and eliminate frequent troubles.

Rich in natural-gas resources, Sichuan Basin where above 2×10¹² m3 of the proved reserves in place had been submitted cumulatively from 2019 to 2023 is one of the most abundant areas in China, which makes the development of natural gas access to the critical era of high quality. Nowadays, shifting to deep or ultra-deep targets, our exploration on conventional gas calls upon advanced drilling and completion technologies as well as better investment guarantee. And for tight gas, with strong heterogeneity in its reservoirs and numerous reservoir types, it's also urgent to upgrade low-cost matching technologies. In addition, as an emerging unconventional energy, shale gas will evolve into an elemental alternative domain for the coming large-scale reserve and production increase. So, confronted with ever-growing hardships in investment control, a management mode of technological and economic integration was discussed to address several issues throughout the natural-gas development and management in this basin, such as investment and unequal benefits, technology and disconcordant economy, and follow-up tracing and adjustment. Results show that (i) linking the entire integration process, a three-level management system is constructed to accomplish closed-loop control across all life cycle; (ii) management is the integration pivot. Employed the three-stage workflow and the five-point closed-loop means, a sort of work environment is set up for the integration to maximize economic profits; and (iii) intensifying organization security, consummating necessary system, fostering talents and building up intelligentization platforms will make the integration come true. It's concluded that, with the brand development of natural gas in Sichuan Basin, this discussion on the management mode of technological and economic integration may provide not only guidance for the cost control in natural-gas development and optimum benefits but reference for both development and management in some other oil and gasfields.

In this study, the full-bore soluble plug was taken as an objective to analyze its key structure for pressure bearing and main controls on temperature resistance in order to meet the need of completion under pressure for internal plugging tools in sustainably upgrading reliability and efficiency. And then a thought was put forward to resolve the contradiction between high-pressure stress concentration and material safety strength. Results show that (i) a safer and more reliable pressure-bearing plugging structure is established by means of the CAD/CAE integrated design method; (ii) in the light of experimental data on high-temperature mechanics, combined with the selected chemical formula of soluble magnesium alloy materials, the best material association is determined, and the contradiction between high-temperature mechanical strength and material solubility is resolved; and (iii) the Plasma-Enhanced Chemical Vapor Deposition (PECVD) method is used to prepare multi-layer nano-protective film, which may effectively improve the corrosive resistance of the plug and ensures its pressure-bearing stability and reliability as well as the quick dissolution in the later stage. It's concluded that this soluble plug boasts excellent temperature resistance and pressure-bearing capabilities besides outstanding corrosive resistance. Without any residue, it can be dissolved quickly after the operation is finished, which is conducive to the next work, and provides a more reliable, green and economical tool for not only completion under pressure but the efficient development of unconventional reservoirs.

Most coalbed methane (CBM) directional wells in Zhijin block are confronted with challenges, such as significant difference in the productivity, short time in the stable production, and unclear productivity controls. So, 23 directional wells deployed at large and small well groups in the study area were taken as examples to analyze the effect of both geological conditions and operational parameters on the productivity. Moreover, the influential degree of different geological conditions and technological measures on the productivity was pointed out for these wells. Results show that (i) the controls mainly include desorption pressure, coal seam thickness, working-fluid volume, lead volume and displacement; (ii) geologically, the average development horizons in large well groups are about 4 times those in small ones. And No. 16, 17 and 21 coal seams are better than others in terms of sedimentary environment, preservation conditions and reservoir structure; and (iii) the working-fluid volume, lead volume and displacement have a great impact on fracturing stimulation. Practical data indicates that, at a certain displacement, the stimulation effect is better when the working-fluid volume is about 5 times of the lead volume. Two conclusions are made. In addition to great in quantity, the coal seams in Zhijin block feature small in thickness, layer spacing and heterogeneity difference in vertical. Thus, a better effect may been achieved from multilayer commingled production by directional wells, and the overall effect in the lower to middle coal groups is better than that in the middle to upper groups. What's more, various stimulation scale and methods have a great impact on the productivity. For the Zhijin coal seams which are provided with high coalification and less brittle than the other seams or shale reservoirs, to raise the proportion of lead volume is helpful to induce fractures better, thus to scale up the stimulated reservoir volume.

In this study, perforating parameters were discussed to increase both productivity and economic benefits in oil and gas wells. And an evaluation index system with multiple attributes, including casing safety as well as perforating bore parameters and skin coefficient in perforating channel, was proposed after analyzing physical mechanisms and their controls on the perforation. And then the parameter impact on both safety and efficiency was fully accessed. Additionally, a decision-making model was set up on the basis of one Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to optimize the parameters. It can effectively calculate individual parameter's weight, put them in order, and find out the best parameter combination. Results show that (i) the proposed TOPSIS-based model can optimize perforating parameters and improve perforating efficiency; (ii) it ensures the wells in safe operation and reduces operational risks; and (iii) its application significantly raises economic benefits. All above results prove this model's availability and superiority. Compared with empirical and traditional well-testing methods, this model provides more assists in scientific decision-making. In conclusion, the research results suppose a new scientific decision-making methodology to optimize perforating parameters, which is helpful to guide practical perforation, optimize completion, advance production performance, and offer theoretical support and actual guidance for benefit increase.

Using reservoir engineering approaches, we dynamically discussed an actual operation in Wen 96 underground gas storage (UGS) from two aspects of water invasion and small range in pressure run constraining both storage capacity and production achievement. And several countermeasures were also made for this achievement. Results show that (i) four technologies, which are conducive to achieving both storage capacity and production in this UGS, contain edge water control, well pattern control, injection-production engineering without tripping tubing string, and pressure enlargement. The injection-production well pattern is further improved by the newly drilled adjusting and renewal wells to draw upon not only working gas volume at the late injection-production period but marginal uncontrolled reserves in the upper submember of the Paleogene Shahejie 3 Member. As a result, the incremental working gas volume is 0.35×10⁸ m³; (ii) mechanisms on production run are optimized to condition the edge-water invasion after core experiments to evaluate this invasion affecting both storage capacity and working gas volume; (iii) some injection-production measures are taken to solve liquid accumulation and salt precipitation so as to improve injection-production capacity; and (iv) the injection-production pressure range is enlarged to meet the UGS's run under the designed maximum and minimum pressure of 27 MPa and 12.9 MPa on maximizing the recoverable production. It is concluded that the stated results contribute to expanding the capacity on the basis the capacity achievement to ultimately improve the working gas volume.

Gas reservoirs of Xujiahe Formation, Dongfengchang area, central Sichuan Basin, are characterized by extra low porosity and permeability, high water saturation and normal pressure, leading to terrible effects in their stimulation and stable production after the early regular fracturing. Thus, we discussed fracturing technologies via an example from the new DF109H well in order to draw on the low-grade gas reserves in this formation. Geology-engineering integration technologies were appeared through a series of research to reduce reservoir damage, speed up flowback, enlarge stimulated bulk, and realize efficient proppant placement. Results show that (i) one system of working fluid which is composed of energized prepad liquid nitrogen and water-based drag reducer can increase flowback energy in tight gas reservoirs with normal pressure, so as to advance liquid drainage and cut down reservoir damage, and to make a rapid breakthrough in deliverability; (ii) sweet spots of both mud and well logging are selected for perforating, and differential high-density fracture arrangement is conducted. Large displacement and composite temporary plugging are used to enlarge the size of hydraulic fractures, decrease flow distance and raise distal supply capacity; and (iii) that fractures remain effective for a long time is the key to stable production. Fiber and dispersing agent are injected through pulse plug during sand fracturing so that proppant is placed more uniformly. In conclusion, with fine fitness in the tight gas reservoirs, these technologies may increase the production substantially and become considerable measures for the efficient reservoir development in Dongfengchang area.

In order to safely and efficiently develop coal-rock gas reservoirs of the Permian Longtan Formation in Sichuan Basin and ensure the effective substitute of natural gas in Sichuan-Chongqing area, it is necessary to ascertain development difficulties in coal-rock gas wells with this formation as the target and to solve frequent accidents and complexities. Thus, taking JT1H well, a key exploration one deployed by PetroChina Southwest Oil & Gasfield Company as an objective, we discussed its sticking points in engineering and geology, including fractures developed within coal rocks, poor drillability resulted from complex lithology, large variation in wellbore trajectory, and inconvenient control on drilling-fluid performance. Then, complexity treatment was analyzed from four aspects of wellbore trajectory, drilling-fluid system, drilling parameters, and precise sticking prevention. Results show that (i) the five-stage trajectory is adopted, which reduces the dogleg degree with effect to satisfy the need of safe drilling for a horizontal interval over 1000 m long; (ii) giving full play to the geology-engineering integration and predicting coalbed thickness, downhole lithology and formation dip can help optimize engineering measures and lesson complexities; (iii) a method which may control the key drilling parameters in horizontal intervals like weight on bit (WOB), rotation speed and displacement is established to diminish coalbed scour and formation collapse; and (iv) lithologic elements are analyzed to detect high-density and high-hardness coal gangue in time and avoid sticking. In conclusion, the compound drilling technologies of efficient PDC bit + rotary steering tool + screw improve the rate of penetration and ensures the drilling rate. With the cumulative thickness of 219 m and the horizontal interval of 1160 m, there are 6 coalbeds of Longtan Formation safely drilled in JT1H well by virtue of these technologies. To deal with abnormality in drilling parameters, to adopt shale shaker, all-in-one machine and centrifuge with effect, and to develop coal-ash mechanical defoaming may cut down pipe sticking. In addition, promoting safe drilling technologies is of guiding significance for the further study on coal-rock gas development in Sichuan-Chongqing area.

With rich water, some tight reservoirs in Dongsheng gasfield along the northern margin of Ordos Basin were studied to ascertain production performance in commingled-producing wells and further guide the highly efficient development. This performance was individuality analyzed for single and commingled wells at various development stages, in different well areas or in the vertical. And controls of gas-bearing property between layers on the performance were discussed for the commingled ones. Results show that (i) such commingled ones have characteristics of high initial pressure and production, but their overall performance is correlated with both gas-bearing property and water production in the tight reservoirs; (ii) after parameter comparison, the performance in payzones has clearly positive correlation with physical properties and gas-bearing property, and the property difference between payzones also affects this performance; and (iii) the critical liquid-carrying (with foam) flow rate during stable production period is certainly related to water/gas ratio. It is concluded that, for the commingled-producing wells with relatively high initial pressure and production, their overall performance, however, is poor in somewhere with low gas saturation (high water/gas ratio). The interlayer production in the vertical is still evolving as the development time goes on. The better the physical properties and gas-bearing property are, the better the production performance is. The physical properties are dominant. Nevertheless, if there is large difference in the gas-bearing property between layers, gas and liquid are highly prone to severe backflow, resulting in not good overall performance. The higher the water/gas ratio is, the greater the critical liquid-carrying flow rate is.

In order to further reduce drilling costs, improve single-well production and solve problems existing in the replacing of "rotary steering + oil-based drilling fluid" with "conventional power tools + water-based drilling fluid" in horizontal wells with long intervals, several technologies were applied to such wells in Sulige gasfield to achieve the low-cost development. Results show that (i) the "dual two-dimension seven-interval" trajectory can deal with drilling tools' bending and some difficulties in setting screw tool face; (ii) both mathematical modeling and engineering intervention can enhance the degree of hole cleaning with effect; (iii) one technology integrating wellbore pressure monitoring with floating casing running can complete smooth running; (iv) the technology of near-bit GR geosteering can boost the drilling rate in sandbody; and (v) the organic salt drilling-fluid system is able to guard against downhole collapse and lost circulation effectively. The application of these technologies makes the friction during the trip and the drilling torque individually reduced by 11% and 17%, and the composite rate of penetration increased by 28%. As a result, the drilling costs are cut down. In conclusion, this technological success provides a basis for the low-cost development of horizontal wells with long intervals in Sulige gasfield and creates novel ideas for improving both quality and efficiency in oil and gasfields.

With rich water, some tight gas reservoirs in Dongsheng gasfield along the northern margin of Ordos Basin were taken as objectives to make clear the interlayer interference in commingled-producing wells and its main influential factors and to guide the efficient development of commingled wells in similar reservoirs. Moreover, controls of reservoirs' geological conditions and stimulation on the contribution of each payzone in commingled wells were analyzed to determine the influential factors on this interference in such well type. Results show that (i) the contributing rate is dominated by porosity, permeability and gas saturation in each payzone, among which the porosity is the leading contributor; (ii) reservoir fracturing plays a great role in production increase, but it exerts a little effect on the contributing rate; (iii) as for the tight gas reservoirs with rich water, the gas saturation is a key element impacting on this rate and interlayer interference; and (iv) diversities of magnitude order in porosity, permeability and gas saturation among different payzone may affect directly the interference degree. In conclusion, the production contributing rate of each payzone in commingled wells increases with the porosity, permeability and gas saturation. What's more, the interference degree raises with the diversities in these three properties. The interlayer interference is quite severe and should be governed as early as possible if the porosity, permeability, and gas saturation diversities are larger than 1.248, 2.69, and 1.22, respectively.

Oil and gas exploitation during the 13th Five-Year Plan was confronted with challenges of complex geological conditions and terrible wellbore situations as it advanced towards some fresh domains of deep to ultra deep or unconventional reservoirs. Secure development puts forward higher requirements for all process, equipment and staffs of well control. So, taken PetroChina Chuanqing Drilling Engineering Company Limited as an example, some difficulties to prevent and control overflow were figured out. Then, countermeasures were made exclusively from five aspects of management, process, equipment, informatization and emergency response through "densifying all-around well control management, perfecting control technologies, upgrading control equipment, boosting overall informatization, and enhancing emergency response ability". Results show that (i) there exist profound control risks in the exploration of deep to ultra-deep petroleum, and the geology and engineering integration in depth is a fundamental measure to increase the accuracy to predict reservoir pressure while decrease overflow risks; (ii) the digital and information-oriented overflow prevention and control, as an essential development tendency, shall be expedited; (iii) both upgrading and iteration of the control equipment are able to ensure this prevention and keep away from certain risks in those deep to ultra-deep wells, and the gradual equipment automation and intelligentization is critical in the future; and (iv) professional control personals are the key to prevent and control overflow, and it is necessary to cultivate "management + on site" individuals in a row, and stress the post-skill assembly and ability promotion of base teams.

The productivity in southern Yongchuan gasfield was evaluated in an effort to sustain the efficient development in complex structure areas. Based on this evaluation, some controls of geological, drilling and fracturing parameters on this productivity were assessed quantitatively by means of single factor analysis and gray correlation. In addition, the optimized well locations in such areas were pointed out. Results show that (i) the study area is characterized by huge variations in burial depth, well-developed faults and fractures, and complicated in-situ stress, bringing about great challenges in its development. Because of strong heterogeneity, this productivity varies intensely in different wells and is controlled by a variety of factors; and (ii) as for the development of shale gas in the complex structure areas, it is unavailable to keep parallel to faults or give up an included angle with in-situ stress. The closer one gas well is to major faults, the poorer the productivity is. Better productivity can be gained while penetrating through minor faults. In conclusion, the productivity of shale gas wells in the complex structure areas is mainly influenced by drilling length in high-quality reservoirs, faults, sand-fracturing intensity, cluster spacing, and wellbore trajectory and azimuth. What's more, it is suggested to adopt the horizontal-well optimization deployment of "long horizontal interval, shallow burial depth, large included angle, and staying away major faults but penetrating through minor ones", namely selecting shallow reservoirs above 3,800 m in depth, ensuring the drilling length over 1,500 m in quality reservoirs, holding the included angle between horizontal-well azimuth and maximum principal stress more than 60o, keeping away from level-A major faults while the penetrated minor faults below level C.

As a kind of considerable energy resources, shale gas is one of principal forces in production growth of natural gas in China. To predict its production accurately is crucial to the rational planning of shale gas utilization. Thus, correlation analysis on production dimension was implemented in an effort to solve a difficulty in this prediction, such as complex influential factors with dynamic changes, and further to improve forecast accuracy. The tubing pressure, casing pressure and water production as independent variables together with the gas production as an dependent variable were put into one prediction model. Then, a combined CNN-LSTM-ATT (convolutional neural network-long short-term memory-attention mechanism) model was constructed for multi-variable prediction. In this model, CNN is used to extract characteristics from production data, ATT enhances the importance of characteristics to input effect, and LSTM is good at learning how to deal with time series data. Results show that (i) the correlation analysis can screen out the dimension affecting intensely the production prediction, which is also of great significance to subsequent prediction; (ii) the multi-variable prediction through the combined neural network model can better forecast the next production trend for shale gas wells; and (iii) better prediction effect has been obtained from this combined model than that from single neural network. In conclusion, with good applicability, the constructed model can increase the prediction accuracy on shale gas production and offer more reasonable prediction, which is meaningful to guide shale gas development.

For both active and safe development for Sinian gas reservoirs, eastern Sichuan Basin, and ensuring effective replacement of natural gas in Sichuan-Chongqing area, it is essential to figure out development challenges in Sinian gas wells to further deal with usual complexity and accidents. So, YT 1 well, the key exploration one which belongs to PetroChina Southwest Oil & Gasfield Company, was taken as an objective. And then, some geological difficulties existing in this drilling were put forward, including multiple sets of formation pressure, large window of pressure system, heavy lost circulation and wellbore shrinkage. Additionally, many treatment technologies were established for the complexity in terms of casing program, leakage stopping, anti overflow and anti collapse. Results show that (i) five-spud nonstandard program should be optimized as an optimal one for setting position in effective package; (ii) three schemes of leakage stopping while drilling, compound leakage stopping and cement plugging should be employed at big hole from the Lower Jurassic Ziliujing Formation to the Upper Permian Longtan Formation. As a result, the success ratio of leakage stopping can be improved with effect to decrease the complexity's incidence rate; and (iii) bottom hole assembly should be chosen at the hole of 241.3 mm from the Ordovician Shizipu Formation to the Upper Cambrian Xixiangchi Formation. And some complexity, like overflow, lost circulation and collapse, is treated to increase drilling efficiency. Five conclusions are made. First, there are no complexity or accidents during air and mist drilling from Shaximiao to Lianggaoshan formations, obtaining an obvious effect in anti-leakage and ROP increase. Second, hydroscillator+ compound bit+ MWD directional drilling, as the best technology for Longtan to the Lower Cambrian Qiongzhusi formations, runs 23 trips in the gypsum salt bed with the well interval of 3150.94 m. Third, 185 mm bidirectional microreamer is tested after drilling 190 mm hole, which may solve hole shrinkage in long gypsum salt bed and ensure smooth running to the expected position after triple ream. Fourth, after the application of treatment technologies to YT1 well, the incidence rate is decreased by 17.47% to avoid heavy pipe sticking. Fifth, these treatment technologies established for the Sinian gas reservoirs in eastern basin are meaningful for studying technologies used in deep wells of the same reservoirs in the whole Sichuan Basin.

In order to sufficiently study the feasibility of short tie-back inserting and setting integrative cementing in the tie-back cementing of complex and deep wells, Shuangyu X well in Sichuan-Chongqing area was taken as an objective to analyze its suitable cementing tools and ensure cementing safety and quality. Results show that (i) this well is one extra deep well deployed in Shuangyushi structure, northwestern Sichuan Basin, which the liner of Φ168.3 mm in five-spudding hangs at the well depth of 5,688.01 m. It has to accept twice tie-back cementing in an effort to ensure cementing quality. To assure the sealing integrity of the cement sheath outside the first short tie-back string, the inserting and setting integrative cementing is adopted, which means to insert the string directly into the flared cylinder and set it after cement injection into the tie-back casing, but not using the conventional swirl nipple at the string bottom any longer, and hence there is no flow hole of swirl nipple after cementing, and the sealing integrity of casing string and the cement sheath can be guaranteed; (ii) technologically, the effective milling of flared cylinder and the structural optimization of tie-back cylinder and short tie-back release unit ensure the effective inserting and sealing of the lower tie-back cylinder while avoiding risks such as the mid-way setting of the release unit of upper short tie-back and the "flatpole inserting" caused by difficult release; (iii) after the application of CemMater cementing software to the design of slurry column structure and construction parameters, the tie-back cementing quality can be guaranteed. In conclusion, in Sichuan-Chongqing area, the short tie-back inserting and setting integrative cementing tool and technology are available for those wells where one-trip long tie-back cementing to wellhead is out of control, and they can ensure cementing quality while solving gas channeling at bell mouth after liner cementing.

In order to analyze the key controls on ROP improvement and determine the main tool for this improvement, both drilling parameters and bit types were taken as objectives to establish one analysis model for these parameters and another evaluation model for bit, which might analyze hundreds of thousands of wellbore engineering data. Moreover, the effects of different parameters on ROP improvement were made clear, the parameter interval conducive to the improvement was pointed out, and the efficient bit was selected. Finally, one method to evaluate the ROP improvement based on wellbore engineering data was developed. Results show that (i) the approach to qualify the Pearson correlation factor can rank the correlation of drilling parameters (such as weight on bit, rotation speed and displacement) to ROP improvement, so as to guide parameter optimization; (ii) the way of the kernel density estimation may display the distribution of each parameter at high ROP, providing a basis to chose quantitatively the interval; and (iii) effective drilling footage and average ROP are decisive indexes for bit evaluation. The efficient bit can be screened out by extracting these indexes of different bit types from database and taking average ROP and footage as selecting standards. In conclusion, this evaluation method not only makes parameter optimization and tool selection more scientific and analytical endings more intuitive, but provides effective guidance for ROP improvement and a new means to analyze and apply big data of wellbore engineering.

Such blowout out of control is a disastrous accident of serious nature and heavy loss in petroleum domain. Especially, when a "three-high" well (high pressure, high production rate and high sulfur content) is on fire due to blowout out of control, intense flame at wellhead, and strong heat radiation and fluid shock require rescue technologies and equipment together with job safety to reach the highest level, resulting in a complex and endless disposal process. So, some rescue skills from blowout out of control and fire burning were analyzed in terms of their development history, status and direction in order to sufficiently figure out disposal difficulties in this sort of "three-high" wells. In addition, a full set of technological innovations on rescue from onshore blowout was made from aspects of reconnaissance, cooling shield, and cleaning-out & cutting to wellhead resetting. Results show that (i) domestic emergency rescue technologies have been iteratively upgraded to the unmanned operation in high-risk areas near wellhead from the insufficient professional skill and equipment in the early stage; (ii) the innovations can meet the demand of out-of-control rescue wells with high pressure of 105 MPa and production of 1,000×10⁴ m³/d, respectively; and (iii) numerous well-control accidents at home and abroad, such as blowout out of control, fire burning and wellhead leakage, have been successively disposed by virtue of these technologies which have attained to an international advanced level. In conclusion, domestic rescue technologies from blowout out of control and fire burning in onshore wells have been improved a lot. However, it is essential to tackle on their visualization, intelligence and information in the future, and to push them to a new step.

To fully understand the performance of foaming drainage gas recovery in shale gas wells under different hole conditions and clarify the adaptability of this technique, some wells with foaming drainage gas recovery in Changning mid-deep shale gas block, Sichuan Basin, were taken as examples to analyze this recovery running in those wells with various tubing size and well types. Moreover, the adaptability in deep shale gas wells was figured out after some pilot tests on foaming drainage gas recovery in deep Chongqing and Sichuan shale gas blocks. Results show that (i) adopting Ф50.8 mm or Ф60.3 mm coiled tubing as well as Ф60.3 mm or Ф73 mm tubing cannot rely solely on their ability to achieve stable liquid-carrying production for a long term. However, this foaming drainage technique is highly adaptable to tubing size. After the drainage, some typical wells gain better ending with the incremental production about 1.18×104 m3/d on average; (ii) this technique makes wellbore clean and smooths gas flow channel to further enable these wells in the long-term, sustainable and stable production; and (iii) it is more suitable for shale gas wells with the vertical depth exceeding 4,000 m. In conclusion, the foaming drainage performance may vary with tubing size and well types, but is greatly adaptable to shale gas wells using Ф50.8 mm or Ф60.3 mm coiling tubing as well as Ф60.3 mm or Ф73 mm tubing in Changning block. Additionally, the foaming drainage gas recovery is more suitable to mid-deep and deep shale gas wells for its high liquid-carrying capacity, long period of stable production, and ability of wellbore cleaning. And it is worth to popularize.

Jin 30 well area, Dongsheng gasfield, northern Ordos Basin, was taken as an example in an effort to comprehend full production laws in tight gas reservoirs rich in water after the adjustment of working system. And some changes of production dynamic indexes such as pressure-drop rate and EUR were analyzed through the classification of adjusted production wells dependent on the adjusted rate, produced liquid-to-gas ratio, and daily gas production. Then, reasons for these changes were found out. Additionally, new production laws after adjusting production were summed up. Results show that (i) for a few wells with the adjusted production rate downward, the pressure-drop rate is significantly sensitive to the adjusted percent, namely the decrease of pressure-drop rate rises linearly as this percent increases; (ii) the EUR is obviously affected by the produced liquid-to-gas ratio, that is the former increases with the latter; (iii) for others with the adjusted production rate upward, the pressure-drop rate is greatly dependent upon both adjusted percent and daily gas production, namely, the decrease of pressure-drop rate remains stable when the adjusted percent is less than 50%. But it rises rapidly when this percent is above 50% and declines with the increase of daily production; and (iv) the EUR is obviously impacted by the produced liquid-to-gas ratio, that is the former increases with the latter. It is concluded that, among certain wells with the adjusted production rate upward, those with high daily production and small produced liquid-to-gas ratio should be selected for upward production adjustment by the percent below 50%, whereas for others with the rate downward, those with high produced liquid-to-gas ratio should be selected for downward production adjustment by a high percent where allowable for carrying liquid.

For purpose of the successful treatment after mud blowdown in gas wells, well conditions and key pressure parameters need to be analyzed carefully to make a killing plan. So, taken the determination of killing-fluid density, selection of killing patterns, and consideration in killing as objectives, several killing ways were explored under different well conditions. Results show that (i) after mud blowdown, the killing-fluid density can be determined according to both shut-in or bleed-off pressure and formation data; (ii) three ways such as bullheading, displacement, and normal circulating killing can be effective when the conditions are allowable for shut in; and (iii) dependent upon gas production and wellhead pressure, circulating killing or killing of rescue wells can be employed when the conditions are not allowable for shut in. It is concluded that (i) in case of mud blowdown, the killing-fluid density and killing ways should be determined as early as possible; (ii) adequate supply and facilities should be reserved before killing practice in order to secure a normal operation; (iii) pressure should be monitored during killing and measures should be taken to prevent pipes from freezing, blocking and breaking, and protective measures should be kept in place against personal poisoning, environmental pollution or secondary hazards; and (iv) for relief wells, their trajectory should be controlled strictly, and the quality of casing cementing in the upper part should be guaranteed to create better killing conditions.

Gas reservoirs of Suining Formation, Luodai gasfield, western Sichuan Basin, were taken as examples to analyze reservoir characteristics and microscopic seepage mechanism. And then a rational development mode was built for them, also providing guidance for similar tight sandstone gas reservoirs with ultra-low porosity, low abundance and multiple thin layers in the efficient development. Results show that (i) featured with poor physical properties, these reservoirs exhibit frequent interbedding and superimposition of sandstone and mudstone, which assumes as tight ones with ultra-low porosity. Their pore structure is mainly composed of fine pores to microscopic throat with relatively small pore-throat volume ratio; (ii) their original irreducible water boasts moderate saturation and they have larger area of gas-water dual-phase co-seepage, and core experiments under pressure depletion represent middle to higher recovery efficiency; (iii) without bottom and edge water, they belong to constant volume, closed, elastic gas-drive dry gas reservoirs with normal pressure; and (iv) they are characterized by low well-controlled reserves, short period of stable production, fast decline in pressure and production, and long-term low yield under low pressure. It is concluded that (i) geologically, this kind of gas reservoirs feature multiple thin sandbodies interbedded each other, presenting the lenticular extension. And they should be appraised and then developed progressively for enhanced recovery to increase development benefits; (ii) in the initial production stage, the highly productive and enriched zones will be preferentially developed under normal pressure if necessary; (iii) in the stable production stage, multiple layers will be co-exploited through vertical wells, and additional wells will be drilled to conduct interwell replacement for productivity; and (iv) in the production decline stage, some techniques, such as changing payzone in old wells, pressured exploitation, and foaming drainage gas recovery, may be employed to delay this decline. Meanwhile, development adjustment wells will be deployed to further enhance the recovery.

For sake of the full awareness of both technical status and development trend of snubbing service of gas wells at home and abroad, this service in China was investigated at first from aspects of support capability, workload and development direction. Moreover, two kinds of snubbing service used in China and other countries were compared, and main achievements, development opportunities, key risks and limitations were analyzed for the snubbing in China. On top of that, it is also pointed that the China's snubbing service, regardless of certain achievements, needs to be perfected in terms of drill grinding, high-pressure completion, and workover technologies. Results show that (i) boasting advantages in reservoir protection, energy saving and environmental protection, as well as productivity increase and stabilization, the snubbing service of gas wells can significantly prolong production period, reduce E&P cost, and protect reservoirs, thereby facilitating efficient production; and (ii) the snubbing has become a key technology for safe, clean and efficient recovery of conventional and unconventional oil and gas resources, and it is also a critical tool for advocating the concept that lucid waters and lush mountains are invaluable assets and adapting to the national strategy of ecological civilization and the specific action for building Beautiful China. It is concluded that (i) the snubbing technology has a good future in horizontal-well drill grinding, completion under high pressure, potential tapping of old wells, and reducing cost to increase benefits in workover; and (ii) the next effort will be made to accelerate the research and development of workover under pressure, remote and intelligent equipment, along with completion or workover facilities so as to create the snubbing of gas wells with Chinese characteristics.

Automatic control technologies have been applied to process equipment in oil and gas pipeline transportation. The adaptability was explored by analyzing equipment characteristics in order to thoroughly comprehend their importance and effectiveness in this equipment management of oil and gas pipeline and make full use of pipeline transportation. Results show that these technologies play a considerable important role in practical application effects on system management, failure monitoring and gas-transportation efficiency. It is concluded that (i) with the rapid growth of China's economic level, the importance of oil and gas pipeline transportation is on the increase, so it is essential to improve transportation's effectiveness and security; and (ii) the application of automatic control technologies realizes the real-time monitoring and analysis of production data and the real-time detection and identification of transportation failure, fulfills themselves through information technology, and gives expression to not only digitalization but intelligence in pipeline transportation.

There exist many problems during coalbed methane (CBM) development in Qinshui Basin, such as low drilling rate, poor cementing quality and troublesome reservoir protection. Thus, some drilling technologies were studied from aspects of optimization of wellbore trajectory, wellbore structure and supporting process, drilling fluid, and third-spur half cementing in order to improve both fracturing and production effects. Results show that (i) the profile of "double increase and double stability" is employed in trajectory design, and trajectory direction is governed precisely by setting control points; (ii) a third-spud horizontal well can be optimized to the second-spud horizontal well with large borehole (Ф311.2 mm×Ф244.5 mm + Ф215.9 mm×Ф139.7 mm); (iii) a kind of drilling fluid to degrade polymer film is adopted for reservoir protection with effect; (iv) the fishing-type completion tool without plug drilling is used for half cementing in the second spudding so as to avoid lost circulation during cementing; and (v) the key drilling technologies are suitable for CBM second-spud horizontal wells in Qinshui Basin. In addition, after field application, it is revealed that the drilling period is shortened by 30% and the ROP is improved by over 20%, indicating an overall increase in CBM development benefits. In conclusion, these technologies can provide reference for subsequent CBM development.

In the process of natural-gas dehydration production, filter elements cannot be cleaned and withstand pressure, and their filtration area is too wasted. So, both shortages and deficiencies of existing elements were analyzed by taking a certain filter element designed for TEG dehydration device as an example, which has been extensively used in this dehydration so as to make element's application effects better and prolong its service life. And some problems were pointed out, like an integral design without being split, low rate of secondary utilization, high break-off, a limited area of effective contact filtration, easy fall-off of end cap and low filtration efficiency. In addition, a novel filter element was put forward. Results show that (i) this element with new structure is innovatively developed after structural optimization of those existing filters; and (ii) it can overcome many disadvantages in traditional elements, such as difficulty in cleaning, short service life, small filtration area and frequent replacement, and its filtration efficiency can also be scaled up. In conclusion, the newly designed filter element is innovative and practical with obvious economic benefits. It is essential to further optimize its application based on actual production in an effort to achieve one goal of improving quality and efficiency.

Tight gas reservoirs are very easy to suffer from contamination, bringing about difficulties in productivity recovering after reservoir damage. However, a new drainage-production replacement process based on narrow tubing may achieve the low-cost and high-efficiency development in tight gas wells during their whole life cycle. So, a mechanical model of plunger-liquid sectionwas established in the ascending stage of plunger lift, and not only frictional resistance during the ascending of plunger lift based on narrow tubing but working pressure in this lift were analyzed in an effort to provide decision-making reference for preparing its working system for these wells. Results show that (i) the frictional resistance in the plunger-liquid section is affected more by the plunger's movement velocity, and the resistance ratio is 1.85 times of velocity ratio; (ii) at the same movement velocity, tubing with different diameters has the same multiple relationship of frictional resistance; and (iii) as for lifting-liquid volume at the same cycle, the smaller the tubing diameter, the higher the operating casing pressure to meet the working system. In conclusion, the smaller the diameter, the larger the frictional resistance of plunger-liquid section. The recommended plunger velocity of 1.9″ narrow tubing corrected according to the recommended plunger velocity of conventional tubing is from 150 m/min to 215 m/min. What's more, as for liquid-drainage volume at the same cycle, the smaller the diameter, the higher the operating casing pressure to meet the working system, so the cyclic liquid-drainage volume of plunger lift based on narrow tubing shall be reduced appropriately.

Some processes of drainage gas recovery adopted in Changning block were studied in an effort to sustain long-term stable production in shale gas wells and hold up scale shale-gas production. Their influential factors were identified. Then, with respect to controllable factors, one method to optimize process performance was proposed on the basis of an intelligent management platform to complete real-time monitoring and acquisition of production data in shale gas wells. Results show that (i) plunger gas-lift, as one process of drainage gas recovery, which is necessary to maintain the production at the late development stage, has been applied extensively in over 200 wells in Changning block; (ii) this plunger gas-lift system is mainly optimized by adjusting technical parameters depending upon production practice; and (iii) coupling the plunger movement model with the time-sequence neural network and multi-objective optimization genetic algorithm, the method to optimize this system can be developed for shale gas wells. It is concluded that, as an economic and effective stable production technique, plunger gas-lift is one of popular drainage gas recovery processes used in Changning block; the existing way for optimizing the plunger gas-lift system is mostly in trial, which is not certain without any theoretical and predictable instruction, and it cannot realize rapid engineering design; and the newly proposed system has been applied to plunger gas-lift in 21 wells, for which the system has been simulated and optimized. Finally, it is derived that the current system is rational and may provide similar results to those optimized ones, proving that the proposed method can not only effectively guide system optimization but offer technical backup for guaranteeing the process with better performance.

There exist many difficulties in the sidetracking of ZS103 well, such as heterogeneity in cementing plug, big difference between drilling bit and borehole size, hard strata, high pump pressure, limited discharge, and easy shale collapse. So, not only strength characteristics of internal and external cementing plug but various sidetracking technologies were analyzed to overcome these difficulties in order for the successful sidetracking with 149.2 mm bit in 215.9 mm borehole. Bend joint sidetracking was adopted in the early stage, and effective sandwich wall, however, could not be formed due to the external cementing plug with poor quality and too feeble support at the joint, resulting that the sidetracking was in failure. Then, a nature that the strength of inner cement core is higher than that of outer cement sheath was analyzed. Thus, dependent on the other feature that the support point of bending screw was closer to drilling bit than that of bend joint, the sidetracking mode was changed by moving this point downward to sustain the sidetracking of drilling bit with the strength of inner cementing plug core. Eventually, the sidetracking was in success by virtue of directional time-controlled sidetracking technology with bending screw. Results show that (i) the prerequisite for ensuring successful sidetracking is to carefully analyze the quality of cementing plug, lithological characteristics in strata and borehole size at sidetracking segments before the sidetracking; (ii) principle parameters such as drilling time, discharge and tool surface shall be implemented strictly during the sidetracking; and (iii) the hinge to carry on successful sidetracking is to select a sort of sidetracking mode based on characteristics of different sidetracking approaches and wellbore environment. In conclusion, the technology of directional time-control sidetracking with bending screw is worthy of intensive promotion to the cementing plug sidetracking with slimhole, large annulus and heterogeneity .

Featured by deep burial depth, thin thickness and poor wellbore stability, most gas reservoirs of Leikoupo Formation in west Sichuan gasfield belong to tidal flat facies deposition. There existed frequent wellbore instability in 11 horizontal wells, which impacted on development benefits. So, in order to ensure the smooth, fast and successful drilling in subsequent long horizontal wells in this field and diminish instability complexities with effect, several marine horizontal intervals in western Sichuan Basin were taken as objectives to figure out instability mechanisms and the influence of fracture seepage on wellbore stability as well as to make countermeasures. Results show that (i) the main influential factors on wellbore instability in this block are stress, fracture and lithology; (ii) easy collapse is commonly occurred in certain areas with well-developed fractures along drilling direction of minimum horizontal stress, and collapse rocks are limestone or limy dolomite; (iii) when adopting water-based drilling fluid, the rock strength decreases by 11.4%-17.5% and the collapse pressure increases by 0.11 MPa/100 m, respectively; and (iv) when employing oil-based drilling fluid, its immersion and soaking time may not lead to strength decrease if fracture seepage is not taken into account. If considering this seepage, however, the fracture friction coefficient may decline by 12.8%, and the collapse pressure raises by 0.05-0.08 MPa/100 m due to this immersion. In conclusion, both drilling-fluid density window and trajectory of horizontal intervals, which may be obtained from precise prediction, ensure a smooth drilling in 6 long horizontal wells, drop complexities of wellbore instability by 43%, and achieve gas production of (172-325)×10⁴ m³/d in the completion test.

Under such circumstances that China proposes energy saving and emission reduction and constructs a resource-saving and environment-friendly society, making clear multifunctional heating equipment without heat-source response to implement anti freezing and block in deep shale-gas development is of great significance to ensure the safety and dual carbon & emission reduction during natural-gas exploitation. So, we figured out origin mechanisms on both freezing and block of natural gas. Then, based on working conditions of each well, some available programs were prepared to manufacture matched products so as to achieve anti freezing and block with energy saving, efficiency and safety, further to minimize resource utilization and maximize safety factors. Results show that (i) the multifunctional heating equipment without heat-source response creates a kind of vortex among the heated substances through an electromagnetic induction approach, and heating can be conducted dependent on vortex energy; (ii) for pure natural gas, its temperature drops 4-5℃ with a decompression of 1 MPa when water of 0.01 kilogram per one cubic meter of natural gas; (iii) in the process of anti freezing and block in deep shale gas, this equipment boasts very high energy utilization and conversion; (iv) frequency control, affirming magnetic field direction and reverse voltage control involved in the equipment are hot spots at present; and (v) the multifunctional heating equipment without heat-source response meets requirements on station security. It is concluded that our country and firms should further accelerate its application to anti freezing and block at wellbore.

To further make clear the development potential of gas reservoirs of the Lower Permian Qixia Formation, PLB structure, western Sichuan Basin, PT1 well was taken as an objective to analyze reservoirs' geological features, production test dynamic characteristics and stable production. Results show that (i) Qixia Formation in this block is well developed with dolomite reservoirs whose porosity and permeability present a dual-seepage nature. Moreover, well-logging interpretation holds that there is no aquifer, while the other analysis on output liquid deems condensed water produced in PT1 well; (ii) calculated from the volumetric method, Qixia gas reservoirs in PLB structure has OGIP of 81.13×10⁸ m³ and OGIP abundance of 3.08×10⁸ m³/km², respectively; (iii) the production is stable and the production capacity drops slowly during the production test. And this test reveals better physical properties far from PT1 well, for example the permeability between 1.69 mD and 7.46 mD, and seepage conditions near the well do not change significantly; and (iv) after evaluated by three methods, dynamic reserves of Qixia Formation in this well are in the range of (44.3-59.69)×10⁸ m³, and it is predicted that PT1 well will remain 23-a, 15-a and 11-a stable production in the context of three production systems of 25×10⁴ m³/d, 34×10⁴ m³/d and 45×10⁴ m³/d. Especially, this well may keep longer stable production time under the current percolation. In conclusion, Qixia gas reservoirs in PLB structure enjoy huge OGIP, superior seepage conditions, and great exploration and development potential. What' more, during the production test of PT1 well, gas production is stable accompanying with a little condensate water. Its test interpretation suggests better physical properties and great development potential. Additionally, some calculation endings from different methods display huge dynamic reserves in these gas reservoirs with stronger stable production capacity, indicating preferable development potential in Qixia gas reservoirs of the study area.

Oil-based fluid is usually employed in drilling shale gas wells while penetrating reservoirs so as to remain borehole stable, cool drilling bits, hold hydrostatic pressure and protect reservoirs. Meanwhile, there emerged a great deal of oil-based cuttings in this process. To settle their massive storage derived from the development of both shale gas and conventional gas, disposal techniques widely available for the cuttings were analyzed. Moreover, as for by-products preprocessed by high-temperature calcination, the cutting's chemical and mineral compositions as well as microstructure were analyzed by modern analysis and testing methods. On top of that, a reutilization approach of the oil-based cuttings was proposed for the development of shale gas and conventional gas. Results show that (i) the cuttings are not likely to discharge a large amount of NO_x, SO₂ and heavy metals during their calcination; (ii) the content of harmful substances produced in the calcination and the discharged pollutants can be controlled effectively; (iii) the properties of solid wastes from the cutting calcination meet not only the specifications on artificial pozzolanic blending materials but the requirements under applicable national or local industrial standards accepted quality for production of replaceable materials; and (iv) the products from the calcination meet the standards to identify the solid wastes, and boast stable and rational market needs further to create excellent economic, environmental and social benefits.

Most high-pressure gas wells in Kuqa piedmont of Tarim Basin possesses three-extra typical natures in drilling depth, high temperature and pressure, leading to extremely severe and complex production conditions. With the development process in this piedmont, tubing-string failures, like leakage, breakage and deformation, have increased in recent years, creating additional well-control risks. Especially, there exists high-pressure gas channeling in A-annulus to outer annulus or surface once the primary well barrier is in failure, and well-control and environmental risks are unacceptable. Consequently, workover as an exclusive tool can recover the barrier. For purpose of the safe and efficient workover in these high-pressure gas wells, the well killing and complicating workover techniques under different barrier conditions were analyzed by taking wellbore as an objective. Supporting techniques and processes were put forward, including well-killing technique, treatment of primary wellbore string and workover while operating under pressure. Results show that (i) to select a proper well-killing technique depending upon barrier conditions is the prerequisite for the successful workover; (ii) tubing-string treatment methods commonly used in Kuqa piedmont include back-off, cutting and grinding; and (iii) THT packers can be processed by means of grinding and washover. It is concluded that such killing techniques as normal/reverse-circulating squeeze well and treatment of broken/disconnected string in the shallow under pressure are effective for workover in piedmonts; tubing-string fishing after cutting is the most efficient for the primary wellbore string; and washover is the most successful and most efficient fishing technique for the THT packers.

In order to fully understand the adaptability of main fracturing parameters to deep shale gas in Luzhou block and also provide reference for further optimizing these parameters, 80 shale-gas production wells in this block were taken as objectives to figure out the correlation between each factor and total production in the first three months based on static physical parameters. Then, a model for production prediction was established by means of the random forests algorithm (RFA). Finally, with the mean geological parameters as reference index, a fracturing-parameter combination available for the best production was achieved through the particle swarm algorithm. Results show that (i) there are three parameters highly correlated with early stage of production, like gas content, brittle-mineral content and fracturing-fluid intensity; (ii) the TOC, horizontal stress difference, fracturing-fluid intensity, liquid sand-carrying efficiency and average cluster spacing are the main factors influencing on the cumulative production in the first three months; (iii) in the optimal fracturing-parameter combination offered by the model, average segment length and average perforation number in each segment are relatively consistent with the current design parameters, and the other optimal parameters include construction displacement of 15.6 m³/min, fracturing-fluid intensity of 35 m³/m, sanding intensity of 3.52 t/m, cluster spacing pf 7.3 m, liquid sand-carrying efficiency of 11 t/100 m³, and 40/70 proppant proportion of 54%, respectively. In conclusion, optimization schemes for fracturing parameters in Luzhou block are exactly "controlling discharge, increasing liquid and sand contents, reducing cluster spacing, upgrading liquid sand-carrying efficiency and 40/70 proppant proportion". What's more, the optimal fracturing parameter combination may provide guidance and reference for design plan on deep shale-gas fracturing in Luzhou block.

As China's natural-gas transmission system upgrades, the city-gas pipeline network is expanding its construction scale. Risk-based integrity management is an important measure to ensure pipeline safety. In practice, to assess risks in these pipelines is challenging for huge workload of data acquisition and input, long duration, poor effectiveness, big errors, and high requirements for professionals. This paper presents an intelligent system for assessing risks in city-gas pipelines and its main supporting technologies. Integrating an existing system with recent information skills such as high-definition satellite remote sensing, Internet of Things, big data, mobile terminals, cloud computing and artificial intelligence, the intelligent system is made up of perception layer, transport layer, application support layer and application management layer. And it boasts following features, including (i) real-time dynamic evaluation on pipeline risks, involving ubiquitous sensing of risk information, integration and interconnection of pipeline service system, and efficient risk assessment for complex pipeline network; (ii) trend prediction and early warning of pipeline risks, which may be realized through a gas pipeline risk model to evaluate deviation extents from the warning line in each risk status and diagnose both warning necessity and levels; and (iii) smart display of risk status, which is enabled by special database of pipeline risks, pipeline digital twin, and distributed cloud screen display system.