In order to well know the deformation of the ram shaft of wellhead blowout preventer (BOP) under stress in the process of operation and provide theoretical reference for reasonable improving the shaft-end overload, the ram shaft of wellhead BOP (U type) applied to drilling engineering in domestic oil and gas wells was taken as an objective to analyze its finite element based on elasticity mechanics. And the ram-shaft stress was analyzed, the stress concentration positions on the shaft were pointed out, and ram-shaft structure was optimized. Results show that (1) stress concentrates at the shaft shoulder at the end of load bearing part; (2) the circumferential expansion force on the shaft end is the maximum stress direction around the shaft. It is recommended to alleviate this stress concentration at the shaft shoulder by changing the transitional fillet radius of stress concentration zone and to reduce all stress by increasing the shaft-end diameter; (3) the equivalent stress in the optimal design with the same size drops by 23.7%. Whereas the equivalent stress, circumferential stress, and circumferential strain in the design with modified size drop by 61.9%, 49.7% and 48.7%, respectively; and (4) when a horizontal shaft is under parallel force, its circumferential expansion force is the maximum and may bring great damage to brittle coating on the surface of load-bearing cylindrical rod. It’s concluded that the modified design may decrease all stress on the shaft-end surface greatly while reducing the circumferential stress on the coating, so as to improve stability and service life for coating and BOP.

In order to increase the drilling speed and efficiency in western Sichuan gasfield subordinated by Sinopec, 9 drilled wells in Pengzhou marine block were taken as objectives to analyze some factors influencing trajectory control while drilling ultra-deep horizontal wells. Results show that (1) for most carbonate gas reservoirs of the Triassic Leikoupo Formation in western Sichuan Basin, their burial depth is over 6000 m on average and their rocks are tight with poor drillability. Furthermore, the Triassic Xiaotangzi Formation with abnormal high pressure is characterized by multiple pressure system, narrower safety window, and serious circulation loss. After an application of the simplified bottom hole assembly (BHA) to certain strata where blowout and circulation loss coexist, there is more difficulty in trajectory control; (2) as for the second section, the kick-off point is deep, the openhole interval is as long as about 3000 m, and the torque and drag are large, so it needs higher requirement in both tension and torsion strength of drilling tools as well as drilling-fluid properties. What's more, because of long construction cycle, wellbore instability tends to occur after being soaked in drilling fluid for a long time, which may increase construction risk; and (3) part Leikoupo reservoirs of the third section are broken seriously, bringing about collapse wellbore and downhole complexity. Meanwhile, rotary steerable tool is not good enough in temperature resistance and mechanical shock tolerance, resulting in a higher failure rate and more difficulty in trajectory control. In conclusion, the technologies of trajectory control developed for ultra-deep horizontal wells in western Sichuan gasfield are conducive to achieving the goal to increase the drilling speed and efficiency.

On September 30, 2020, all oil and gas pipeline assets held by PetroChina, Sinopec, and CNOOC were handed over to PipeChina, indicating its official launch. In order to ensure these traditional petroleum enterprises to better cope with the change of LNG market caused by this market-oriented reform and the production-transportation-sales separation of natural-gas resources, the latest LNG business development situations in Sinopec as representatives were studied. Furthermore, the change of Sinopec's operation before and after PipeChina establishment and the domestic new pattern of LNG market after this establishment were analyzed. In addition, several suggestions were made from aspects of market development, marketing management, and customer service. Results show that (1) with abundant and quality resources, Sinopec may quickly occupy this new LNG market and achieve a rapid sales growth. However, there is still some aspects which need improving, such as infrastructure layout, profitability, user stickiness cultivation, and market competition; (2) PipeChina establishment may increase the diversity of imported LNG resources, so as to intensify the competition in downstream market while optimizing the allocation of pipeline gas resources and promoting traditional enterprises including Sinopec to shift their focus to the terminal market; and (3) an analysis on SWOT matrix also indicates that PipeChina establishment can provide Sinopec with new opportunities to develop LNG market. And the key to seize the opportunities is to make full use of its own resource advantages, and adopt more sophisticated price management and marketing management schemes focusing on the development and layout of the terminal market.

In order to realize the intensive and efficient construction of gas-storage facilities and avoid both low utilization ratio and duplicated construction which may appear, three problems about the storage capacity of natural gas in Sichuan-Chongqing area were summed up by means of quantitative analysis, containing that the construction of LNG plants and gas-storage tanks may face duplicated construction; most storage facilities are relatively independent without sufficient interconnection, resulting in resource waste; and due to incomplete market mechanism, it’s in essential to establish a profit business model for these gas-storage facilities. In addition, multiple measures were made in facility construction, and several strategies and implementation paths to improve this capacity were put forward so as to guarantee a safe and smooth implementation on production, transportation, storage, and distribution. Results show (1) to stick to the principle of intensive and high efficiency and integrate existing underground gas storages, LNG processing plants, and support storage tanks, high-pressure spherical tanks, depleted gas wells, biogas project land reserves, and other resources to improve the storage capacity; (2) to establish a three-level peak-shaving system and make use of market means to improve facility profitability, which is conducive to revitalizing the stock of storage facilities and improve facility utilization ratio; and (3) to broaden profit channels of gas storage and peak shaving and explore a new business model so as to achieve the win-win effect. In conclusion, with continuous improvement of market, most business and users of storage facilities will increase continuously, the deregulation of price control will make natural-gas storage and production more market oriented, and sticking to the idea of constructing storage facilities intensively and efficiently by integrating gas storages, depleted gas wells, LNG storage tanks, high-pressure spherical tanks, and biogas land resources will effectively make healthy and orderly progress on gas-storage market.

In China, the “3060” goal of carbon peak and carbon neutrality will speed up energy structure transforming towards some low-carbon clean energy, which may certainly and profoundly affect traditional energy. As a kind of low-carbon clean fossil energy, natural gas plays an important bridge and balance role in this energy transformation in the middle to long term. However, it’s inevitably affected by a large-scale growth of new energy. So, based on natural-gas role in domestic energy structure, the opportunities and challenges to develop natural-gas industry in China were deeply analyzed. On the one hand, also as a clean and efficient fossil energy, natural gas will maintain a long-term growth trend. And on the other hand, other renewable power and new energy may also occupy partial increasing space of natural gas demand. In addition, it’s pointed out that domestic natural-gas industry presents some phased development characteristics. Therefore, in order to promote the exertion of its important role and the construction of national safe and reliable diversified clean energy supply system, and to realize the goal of carbon peak and carbon neutrality, many coping strategies which the natural-gas industry should take actively to satisfy a long-term growth were put forward from four aspects, including (1) to insist on a long-term development strategy to promote quality development, (2) to optimize a diversified natural-gas resource supply system, (3) to develop gas power generation to provide reliable support for the transformation of power system, and (4) to promote an efficient natural-gas utilization from demand side to maximize resource value.

At present, the development of shale-gas horizontal wells in China is gradually increasing. So, in order to efficiently develop the quality reservoirs in shale-gas horizontal wells and improve the drilling rate, to control the well trajectory in Wufeng Formation-Longmaxi Formation, W Block, Sichuan Basin, was analyzed. And a set of control technologies were developed, including the target A prediction and segmented well-trajectory control in landing section, the determination of the relative spatial position of the trajectory to the reservoir, and the trajectory control of horizontal section in complex structures. After these technologies were applied to the Wufeng Formation-Longmaxi Formation in the shale-gas horizontal wells, the drilling rate in quality reservoirs was improved, especially trajectory optimization control in complex structural blocks was strengthened. Results show that (1) the application of the precise sublayer positioning and distinguishing technology can accurately determine and judge the distance between bit and reservoirs and their dynamic variation; (2) the adoption of the segmented trajectory technology can ensure effectively dynamic control and is also the key to successful landing and target A hitting; (3) by virtue of the relative spatial position analysis along with the control technologies, the dynamic variation of both bit and reservoirs and their deviation can be figured out in time, so that the trajectory in horizontal section can be optimized and controlled in real time; and (4) after the application of the recognition and judging technology to some complex structural morphology, the drilling rate of quality reservoirs can be effectively improved under horizontal-well geosteer in complex structural blocks.

In Gaoshiti block, Sichuan Basin, most reservoirs are characterized by greater burial depth, and higher temperature, pressure, and sulfur content. So, some complex drilling technologies, which mainly aim at not only those wells with vertically multiple targets and pressure systems but also certain rocks with high hardness and poor drillability, were studied in order to deeply understand fast drilling used in this block and provide technical reference for improving both rate of penetration (ROP) and gas development efficiency in Gaoshiti-Moxi block. Based on recent drilling practices, the reasons why the drilling cycle was long and the ROP was low were analyzed. In addition, some ROP improvement technologies suitable for Gaoshiti block and other optimized fast drilling ones adaptive to engineering and geological characteristics also in this block were developed. Results show that (1) complex lithology and big difference between rock hardness and drillability may bring about a lower ROP; (2) during the whole wellbore drilling, there may be multiple high- and low-pressure layers coexisting at the same open hole, which increases drilling risks; and (3) some strata with the characteristics of high temperature, pressure, and sulfur content may limit drilling-fluid properties, resulting in a narrower density window. In conclusion, to optimize casing program can greatly shorten the drilling cycle of 311.3 mm hole section, and to reasonably use composite bit can significantly improve the ROP. What's more, applying different technological parameter enhancement modes to the strata with different lithology is also the key to improving the ROP in Gaoshiti block.

The bell at the top of tie-back cylinder is easily damaged after liner cementing. So, it is important to develop a limit milling and restoration technology suitable for the cylinder. For the tie-back cylinder in GS001-H20 well, its long bell sealing surface was damaged during milling. Also for GX-2 well, its cylinder milling and restoration brought about tie-back casing not running to a desired location. These two accidents were analyzed. Some problems and risks in existing milling string, milling cone, and milling and restoration methods were studied. In addition, the limit design of ordinary milling cone was carried out, the milling and restoration methods were perfected. The ordinary milling cone was structurally modified and added with the limit device to design the limit milling cone. In this way, for the bell at the top of tie-back outer cylinder, its limit-section long milling and restoration was realized from the level of tool. And the limit milling and restoration technology was developed for the milling cones. Results show that (1) from respects of technology and tool, the limit can both realize an effective milling and restoration for the tie-back cylinder; (2) tool limit milling and restoration is safer and more reliable; and (3) after the application of this technology to GS001-H27 and MX001-H13 wells, the tie-back casing may be inserted into the desired location, resulting in the reliable seal and successful cementing. In conclusion, this developed technology can provide effective and safe milling and restoration for similar cementing problems, and ensure the proper location of tie-back casing and the reliable seal.

In western Sichuan gasfield, most Xujiahe Formation is characterized by burial depth of 2000-4500 m, 1700-3050 m in thickness, and formation pressure coefficient of 1.85-2.0. And rocks in this formation are tight and hard, resulting in a drillability limit as high as 8.0. In addition, an average ROP (rate of penetration) of vertical wells is 1.41-2.22 m/h in the equivalent hole section during the early evaluation. In order to develop this gasfield efficiently, the Xujiahe Formation with lower ROP was taken as an objective to carry out fine engineering geological parameter description, casing program optimization, tool selection to increase the ROP, and drilling parameter reinforcement. And thus, many key technologies suitable for ROP improvement were developed. And six development wells were completed successfully. As a result, the average ROP is up to 3.19 m/h which is 32 % higher year on year, and the drilling cycle is shortened by about 40 d. In conclusion, integrating with engineering geological parameter evaluation, casing program optimization, rock breaking tool selection, and drilling parameter reinforcement, these key drilling technologies available for hard formations are beneficial to the ROP improvement and drilling efficiency in the Xujiahe Formation. They can satisfy the requirements on efficient development of western Sichuan gasfield and provide technological references for optimized and fast drilling in similar gas wells at home and abroad.

In Linxing block, Ordos Basin, which has already stepped into a large-scale development stage of tight gas, newly drilled wells increases year after year. However, there are many drilling challenges in most formations, including tight rock, poor drillability, low ROP (rate of penetration), high drag and torque, and serious bit wear, which may bring about big difficulty to improve drilling efficiency. In order to achieve one target to cost reduce and improve efficiency, some difference between conventional and slim-hole casing programs in aspects of cuttings volume, drilling-fluid consumption, casing amount, cement, rig load, and operation cost was analyzed in terms of casing program, drilling fluid, and bit and bottom hole assembly (BHA). Then, two-section horizontal well with long open hole section and three-section horizontal well were also compared in terms of advantages and disadvantages. Furthermore, several influential laws of the dosage of super dual repellent on surface tension were investigated. In addition, bit-structure design was optimized and BHA was modified. Results show that, for sandstone horizontal wells, both drilling rate and ROP are individually increased by over 10 % and 25 %, and the drilling cycle is shortened by over 3 d, showing these efficiency-improving drilling technologies developed for tight gas can be popularized in Linxing block.

The current casing collapsing strength is usually calculated according to ISO10400 standard. However, this standard treats deviated wells as vertical ones without considering an influence of curved borehole. Some scholars have established formulas for calculating this strength while considering the curved borehole, but the formulas don't include manufacturing defective of casing, e.g. out of roundness and uneven wall thickness. So, it cannot reflect true situation accurately. In order to develop another formula with full consideration on various influencing factors, this study established a new model for calculating the collapsing strength of casing which includes curved borehole and manufacturing defective. Results show that (1) the new model considers the effects of non-uniform load, curved borehole, and manufacturing defective on the collapsing strength, so it can reflect the actual downhole casing more accurately; (2) comparison results also present that the change trend of collapsing strength calculated by this new formula is in accordance with that from one formula developed by Professor Huang Genlu with consideration on the influence of curved borehole and another ISO formula; (3) a 3D model of casing in curved borehole is established by means of finite element software. Both simulation and calculation comparison among the new formula, and the Professor Huang Genlu and the ISO formulas indicate that the result from the first one is closer to the finite-element simulation; and (4) for the calculation result from the newly established model, its change trend and comparison with the simulation result can reflect higher accuracy and precise. These may provide reference for accurately calculating the collapsing strength of downhole casing.

In order to sufficiently clarify the feasibility of applying the top cementing technology to vertically diverse gas reservoirs, some cementing difficulties, twin-packer pipe string structure, and cementing design of positive injection & reverse squeezing were analyzed by taking the Upper Paleozoic water-bearing gas reservoirs and the Proterozoic fractured gas reservoirs in Dongsheng gasfield, Ordos Basin, as objectives. In addition, Φ139.7-mm top cementing was tested and evaluated in many directional wells for the first time. Results show that (1) an application of top cementing technology to Jin 142 well ensures the screen completion without cement contamination in the Proterozoic fractured gas reservoirs and the effective cementing in the Upper Paleozoic water-bearing gas reservoirs; (2) this technology is an important means to form many layered and diverse completion modes under the same borehole diameter, so as to realize fine multi-layer production in vertical direction; (3) cement slurry can be effectively prevented from dropping via adopting the design of twin-packer pipe string structure and selecting one formation with regular borehole diameter and stable borehole wall as the setting position; and (4) the cementing technology of positive injection & reverse squeezing is beneficial to improve the cementing quality for those wells with multiple serious leakage layers in the vertical direction. In conclusion, it can simplify the casing program, save the cost, and prevent the cement slurry from contaminating gas layers. The research result provides reference for the efficient development of domestic vertically diverse tight gas reservoirs.

In western Sichuan Basin, most middle to shallow gas reservoirs are characterized by great variation in burial depth, strong lateral heterogeneity, sandstone interbedded frequently with mudstone, and rich smectite easily resulting in hydration and swelling. These characteristics may bring about many problems, such as low rate of penetration（ROP）and drilling complexity often occurred. So, some key technologies have been developed for the middle to shallow horizontal wells in western Sichuan Basin, including to optimize casing program and wellbore trajectory, to formulate polyamine imitation oil-based drilling fluids with high performance, and to work on special PDC bit and matching high-power drilling assembly. These technologies were applied to 150 gas wells and solved the problems of both low drilling efficiency and large risk in safe drilling. As a result, the average ROP was increased by 30.07 % and the average drilling cycle was shortened by 16.93 d, individually.

Several hazardous substances can be easily found among drilling waste of drilling cuttings and waste water. There are more than ten methods used for waste treatment. However, different methods have their own application extent, and treatment effect and cost. Aiming at five approaches of drilling waste zero discharge, such as plate-frame pressure filtration, extraction, high-temperature oxidation, high-temperature pyrolysis, and efficiently physical separation, the expense structure and cost difference of both treatment while drilling and centralized treatment are analyzed. Furthermore, the main factors affecting treatment cost and three limitations from single pricing method are also presented. And another two-part pricing method is suggested to determine the price in treatment while drilling. This two-part pricing method has three advantages and its application scope. Finally, for treatment while drilling and centralized treatment, the expense structure and its calculation ways are also regulated.

Some problems on well-control risk are becoming increasingly acute along with more and more high-pressure oil and gas wells developed. So, it’s essential to establish a new well-killing way available for wellsite. In this study, combined annular pressure system with equation of gas state, we at first set up a numerical calculation model for this new way storing high-density drilling fluid; and then analyzed the wellhead casing pressure and the variation in pressure around casing shoe in the process of this well killing; at last, compared with conventional waiting weighting well-killing methods. Results show that, by using conventional methods, higher casing pressure may easily bring about loss in many low-pressure or brittle strata around casing shoe; however, adopting this way can decrease higher casing pressure a lot, further reducing loss in these brittle strata. In addition, it is advantageous in short time for waiting, low difficulty, and success-ratio increase. So, the well-killing way storing high-density drilling-fluid in wellsite is more suitable for some wells with high formation pressure, large invasion volume, and narrow density window.

In Fuling area, many technologies of improving ROP in horizontal wells have been developed in order to accelerate the shale-gas exploration and development process. Based on geological features and theoretical study, some technologies increasing drilling rate available for Fuling shale gas have also been developed, including selection of drilling bit, trajectory control of 3D long, stable, and deviated hole, and lost circulation prevention. After their application to 28 shale-gas wells, the average drilling cycle shortens to 11.42 d and the ROP increases by 74.78%, respectively.

In Yuanba structure, Sichuan Basin, the Xujiahe Formation with deep burial depth is composed of sandstone interbedded with quartz resulting to strong abrasiveness, and mudstone with coal which may bring about hydration swelling. During a drilling, there are some problems of low ROP and borehole instability, which seriously restricts a drilling process. So, a technology of underbalanced drilling has been adopted to increase the ROP. However, for this technology, drilling fluid should be capable of higher anti-collapse performance. In this study, a drilling-fluid system, imitation oil-based drilling fluid is optimized, which is characterized by easily adjustable rheology, better wettability, strong inhibition, low filtration loss, and thin, tough, and tight mud cake. This system may drill through the Xujiahe Formation with safety, high quality and speed.

Gas drilling is the main tool for continental strata in northeastern Sichuan Basin to increase the drilling rate. However, it’s necessary to implement a gas and liquid conversion while abnormal situations occur at designed well depth. And after the conversion, borehole instability may bring about some problems of sand carrying and reaming, further to affect economic benefits. So, in order to solve a problem of easy borehole collapse after gas drilling, an anti-collapse measure to implement the pretreatment of wettability alteration using oil-based prepad fluid is presented, and a technology of rotated spray conversion is developed. By adopting the original drilling assembly, this technology can realize the reaming and increase the efficiency of gas and liquid conversion. As a result, the total conversion time, which the original one was between 5d to 22d, is cut to 4d.

Gaomiaozi gasfield in Zhongjiang area is an important one deployed by Sinopec Southwest Oil & Gas Company targeted the continental gas exploration and development in western Sichuan Basin. The previously used casing program of one-one-one system only relied on early acknowledge of geological characteristics and experiments on segment reconstruction process, which might bring about a long drilling cycle and high cost. Then, another one-one system was optimized, however which led to many complicated conditions in its application in 2014, not only affecting completion schedule severely but also increasing the difficulty and risk in well logging and casing running. In this study, based on an optimization of both setting position and each bore casing depth, a demonstration was carried out to optimize the casing program of middle to deep horizontal wells in this field. As a standard casing-program plan, the completion of liner hanging without tie back was presented. The standard plan was applied to drilling and completion in 2015. Compared with the one-one system, it can shorten the drilling cycle by 7.4% on average, increase the drilling rate by 21.7% on average, decrease the drilling time by 22.3%, and reduce the bit cost per meter by 18%, respectively.

In one gas power plant, there is still a problem of a certain differential pressure loss even though an adjustment by pressure regulators. So, a design method to use expansion machines replacing the regulators was developed to achieve pressure stabilization of superchargers and make both expansion machines and superchargers in a coaxial location. Further, the utilization of natural-gas cold energy at the outlet of expansion machines was analyzed. Results show that it’s unnecessary to add a heating facility to increase the capacity of expansion machines before gas in unless there is excess heat in this power plant to make natural gas warm.

Methanol is used as a hydrate inhibitor in Daniudi gasfield, and its filling-up quantity may be guided by a software called PIPESIM simulator. However, as one of parameters in the simulator, the temperature change along the buried gas pipelines is still unclear. So, through this simulator, the hydrate-generating curves showing the key point to generate hydrate gain. Moreover, by means of another FLUENT simulator, the temperature drop along pipelines also obtains. And temperature is calibrated on the basis of geotemperature monitoring data. Subsequently, a model figure of temperature drop along pipelines forms. These can guide how to use a temperature-drop model along pipelines under different seasons.

In eastern Sichuan Basin, the geologic conditions are very complicated, including big variation in strata and also large stratigraphic dip for high-steep structures. So, during drilling the upper strata, deviation often occurs easily, which bring about a difficulty in ROP improvement. Furthermore, some passive anti-deviation tools such as tower drilling assembly, pendulum drilling assembly, and packed hole assembly are used to control borehole deviation by means of reduction of drilling pressure. However, their anti-deviation and straightening capacity cannot meet the demand the ROP improvement for complex, directional, and high dip wells yet. In order to solve these problems, some key technologies have been developed, including air hammer anti-deviation one, VTK vertical drilling one, triangular drilling collar with roller reaming anti-deviation one, and bended screw with MWD anti-deviation vertical drilling one. After their application, the ROP improvement was evident. These tools provide useful search for anti-deviation while fast drilling in high-steep structures.

In Gaomiaozi area, borehole instability often appears in many long intervals, further affecting a safe and smooth drilling. The location or zone where there is borehole instability may be confirmed through actual drilling, well-logging analysis, and experiments. We implemented a series of study on the optimization of inhibitive plugging agent and the reasonable data point of drilling-fluid density, developed some anti-sloughing drilling-fluid technologies, and applied these technologies to two horizontal wells in Gaomiaozi structure. Results show that adopting drilling fluid to inhibit plugging property can effectively shorten the time of both tripping and drifting before casing running, increase drilling efficiency, and decrease complex accidents.

In mud shale, there are large amounts of water-sensible clay minerals. When in contact with drilling fluid, the mud shale interacts with drilling fluid each other, which may lead to swelling due to hydration. This alters the stress distribution near borehole. And one problem of borehole instability in mud shale becomes more serious than that of stress instability in conventional constant elastic parameters. So, it's more difficult to predict borehole collapse cycle. Our study deems to establish a quantitative correlation between borehole stability and change of drilling-fluid soaking-time. To make rock mechanical parameters clear is very important in this correlation. So, through some experiments, the first relationship that these parameters changes with soaking time is established; and then, the second one that collapse pressure varies with time is set up; at last, the third one that collapse width changes with soak time may be gained. It's demonstrated that one cycle should be no obvious change that the width increases. At this time, borehole stress reaches a balance again. This procedure avoids a complicated mechanical and chemical match, and finally can realize an aim to predict the collapse cycle very accurately.

In micro-flow controlled drilling technology, downhole complicated conditions are mainly estimated by real-time monitoring of inlet and outlet flowing variation of drilling fluid, and wellhead back pressure is adjusted through the opening control of throttling devices. However, by downhole micro-flow tool, the function of real-time transmission can be achieved to provide a guarantee for controlling micro-flow rate efficiently and accurately. Thus, a real-time transmission system of downhole micro-flow measurement is designed. With the system, the signal of downhole tester can be transferred to the ground through MWD, providing some parameters about back pressure and flow control. Its main advantage is the fast processing for accidents of downhole overflow and lost circulation. If there is no accident, it just needs to maintain the stability of annular flow rate and annular pressure; but if many accidents related to pressure occur, the mechanism of pressure control will start to adjust downhole flow and pressure through estimating the annular flow variation and the gas content of invading fluids combining with wellhead parameters.

JY1HF well is the first shale-gas horizontal well deployed at Jingyan-Qianwei block of Weiyuan structure, southwestern Sichuan Sag, Sichuan Basin. Its target interval is the Cambrian Qiongzhusi Formation and the drilling depth is 4623 m. There are lots of difficulties during drilling this deep marine strata, containing poor drillability, strong abrasiveness, long horizontal length, and low cementing quality under long openhole or by oil-based drilling fluid. So, some technologies were applied to this well, including highly efficient optimization of drilling bit, turbo drilling, PDC bit integrating with oil-resisting motor drilling, oil-based drilling fluid with strong sealing capability, and optimized casing string and slurry system. Better effects were obtained, for example, the drilled horizontal length of 1203.72 m, the average ROP in the marine strata increased by 96% compared to some adjoining wells with same hole size, the average ROP in this shale bed raised 6.1 times faster than those adjoining wells with same hole size, smooth well trajectory, casing running right the first time, and excellent cementing quality.

In this study, a model of steady-state drill stem and annular flow has been developed. Meanwhile, this model is coupled with another model of wellbore pressure, temperature distribution, and relative humidity of wellbore. And the distribution of wellbore pressure, the maximum humidity ratio, the distribution of relative humidity, and the critical formation-water yield and critical relative humidity under a dewpoint may be obtained from a numerical simulation. Results show, when the relative humidity is higher than the critical relative humidity, even though no condensate found in wellhead or only appeared in bottomhole, some downhole complexities will happen along with the constant effect of formation water on cuttings and sidewall.

In southern Sichuan Basin, there are abundant resources of shale gas. For these shale-gas reservoirs, the burial depth varies from 3 600 m to 4 100 m, and many risks of incorrect casing running and poor cementing quality often appear during a cementing. So, a suite of key technologies conducive to increasing cementing quality were developed, such as strengthening a drifting, optimizing string structure, optimally selecting a center device, and adopting four-class cleaning ways. After their successful application to three wells including JY1HF well, high cementing quality was obtained, over 92.5 % especially occurring at horizontal and deviation sections.

During a slim-hole sidetracking for extra-deep and hard formations, the first sidetracking is always inefficient due to both build-up rate of drilling tools and hardness of formations. So, it's very critical to adopt suitable drilling assembly to increase this rate. Taking the sidetracking of 10-1H well in Yuanba area as an example, we analyzed some factors affecting it successful sidetracking, discussed how to select the drilling assembly, and optimized this assembly. Results show the best assembly for the hole of ∅165.1 mm in this area should be the PDC bit of ∅165.1 mm, the straight screw of ∅127 mm, and the 2.25°bending joint of ∅127 mm, individually.

In offshore drilling, the variation regularity of drilling-fluid temperature is different from that in conventional drilling. The rheological property of drilling fluid dominated by the wellbore-temperature variation may impact drilling operation. So, it's necessary to make clear the variation to establish a mathematical model of wellbore-temperature distribution based on the energy conservation relation and heat transfer theory. Meanwhile, a sensitivity analysis is carried on by using numerical simulation in order to formulate a mathematical method for the temperature distribution. The variation regularities of sensitivity obtained include:（1）with the increasing displacement, the wellbore temperature above mud line increases whereas another under this line decreases;（2）as injection temperature goes up, the wellbore temperature above the mud line increases but another under this line remains the same; and（3）an insulating layer may reduce the range of temperature variation above the mud line, which is conducive to stabilizing drilling-fluid property.

Write the pressure gradient component in Darcy’s law into quotient of two power product, and insert disturbing term with same exponent into denominator, to have no reduction of the fraction, leads to a constitutive equation which can describe the phenomenon of ‘nonlinearity’ (between macroscopic velocity and pressure gradient of the fluid) when fluids flowing in porous media at low velocities. Replace speed with function of radius in the ‘hyperbolic non-linear’ constitutive equation, then gain the symbolic solution of the non-homogeneous non-linear ordinary differential equation of first order, which is an explicit function associating pressure with radius in two-dimensional or three-dimensional radial steady velocity field. According to which, can we raise the detective idea about pressure gradient varying in space of whether the said ‘nonlinearity’ exists or not, to realize different macroscopic velocities coexist in the same pressure measuring and avoid macroscopic velocity measuring of the fluid. Just because it is difficult to grasp various relaxation time uniformly and measure low velocity accurately, that is deemed to cause the false appearance of the said ‘nonlinearity’.

For the lower Paleozoic Majiagou Formation, Sulige gasfield, its burial depth reaches 3400 m. And this reservoir is composed of carbonate rock, resulting in a poor drillability. Longitudinally, Majiagou Formation and Double-Shi Formation (also Shiqianfeng and Shihezi formations) derived in the leakage and collapse during a drilling, respectively; massive coal seam can be found in Shanxi, Taiyuan, and Benxi formations; and complex geological conditions may strongly affect a drilling speed. So, we implemented some research and field experiments, especially anti deviation and drilling-speed increasing in vertical well section, PDC bit optimization matching with positive displacement motor, well trajectory control in horizontal well section and bottom-hole-assembly optimization, geo-steering in horizontal well section integrating with directional drilling, and compound salt polysulfonate drilling fluid. Finally, a new technological pattern to increase drilling speed, available for this structure, formed. After its application to Su 5-16-46AH well, the drilling depth and the horizontal-section length were 4600 m and 801 m, respectively; the drilling cycle decreased to 43.85 d from 64.08 d, and the ROP increased from 6.32 m/h to 8.77 m/h, also a 38.8 percent of increasing rate. Consequently, a safe and fast drilling can be realized for some horizontal wells in this structure.

During drilling the Xujiahe 5 sandstone reservoir, western Sichuan Basin, some probably drilled long shale intervals may easily lead to wellbore instability. So, in order to guarantee a drilling safety in these intervals, a water-based drilling fluid with high quality has been developed to improve the inhibition and plugging performances for some conventional water-based drilling fluid. Its application to XYHF-1 well shows that (1) this high-quality one can reduce significantly instability rate for shale; (2) however, the instability risk increases gradually with drilling time; and (3) this water-based drilling fluid needs to be replaced with oil-based one in time. Relative to the water-base one, the oil-base one can not only meet the requirement of wellbore stability but also raise the penetration rate and shorten the drilling cycle.

Compared with conventional drilling technologies, the gas drilling has evident superiority in discovering and protecting reservoir, reducing drilling complexity, and greatly increasing drilling rate. Furthermore, compared with gas normal circulation drilling, the gas-lift reverse circulation drilling has advantages of both low investment and effective protection for low pressure reservoirs. During drilling Wenquan 2 well in Xiannushan Mountain with 215.9 mm borehole, some complex situations, including formation water, lost circulation, and collapse might occur. It is hard to overcome these difficulties by conventional drilling. So, this gas-lift reverse circulation drilling was applied to Wenquan 2 well and its drilling depth achieved 185 m. Finally, these difficulties were overcome and the well was drilled successfully.

As a new one, double-pendulum drilling tool is being used in many major oilfields. But so far, no document illustrates its working principle. In this study, based on the effect of tool shape on penetration rate, the reasons why the conventional drilling is inefficient are analyzed; the working principle of double-pendulum drilling tool is presented; and the application effect of this drilling tool is compared with that of positive displacement motor and torque impactor. Moreover, according to its application to Shuangxing 1 well, the speed-raising effect is analyzed. Finally, a conclusion that this double-pendulum drilling tool may control instantaneously the swing and whirling motion state of drill string, obstruct bit inclination, mitigate bit bounce, and protect bit is made.

As a sandstone reservoir in Akmomu gasfield, Kizilsu Member is mainly dominated by both feldspathic litharenite and litharenite, and is characterized by poor physical properties with low porosity and permeability. Since 2013, the Kuche Project Department of PetroChina Tarim Oilfield Company has applied some selective cementing and completion technologies to two horizontal development wells, AK1-H3 and AK1-H6, which are situated in Akmomu structure of Kashgar Depression. After that, this reservoir was successfully protected and its production increased. Taking 127 mm selective drilling liner cementing technology for AK1-H6 well as an example, this paper presents its principle, string structure, technical measures and field application. This technology can prevent a payzone from contamination and increase production.

Jiangsha 33-6HF well, which is located at the Zhongjiang-Huilong nosed structure, western Sichuan depression, is a horizontal well with a system of two opening. During its drilling, the JS₃^3-2 sandstone layer was taken as the main target zone, and the design depth and length of horizontal interval were 3 784 m and 904.5 m, respectively. However, a situation of short circulation happened during its liner cementing. So, some measures against this situation, including finding out failures, milling, and pressure testing, were used to finish an oil test which might meet the requirement of a later production. Even though the short circulation happened during a cementing very rarely, some aspects of short circulation are presented in this paper, such as its processing and cause. In addition, many protective measures to carry on an annulus pressure test and to test a lag time of short circulation are made.

Yuanba continental strata are the key exploration and development targets for Sinopec due to their abundant natural-gas resources. The main target zones, both Ziliujing and Xujiahe formations, are characterized by HT and HP, and tight lithology. For a technology of horizontal-well drilling, its advantage is to increase the drilling-encountered ratio of natural fracture. However, there exist some problems, including low deflecting efficiency of deviated interval, and low penetration rate, resulting in long drilling cycle in deviated interval and full hole. So, some other drilling technologies were applied to the Shaximiao Formation in 8 wells from casing-program optimization, shallow-optimized-fast drilling, bit optimization for high-abrasiveness formation, trajectory control of deviated interval, and high-quality drilling fluid. As a result, the drilling rate was increased very obviously. And the average drilling cycle is 212.68 d, and average penetration rate reaches 2.08 m/h, which is 39.7 % faster than that of previously drilled LY301 well.

Some problems occuring in a conventional drilling in Huobei area, Junggar Basin, include low drilling rate and long drilling cycle. So, some technologies of gas underbalanced drilling should be used to shorten the drilling cycle and speed up an exploration process. Here, many gas drilling technologies, containing mist drilling, casing running cementing in a dry hole, coring, and air and/or mist drilling-fluid conversion, are presented in terms of their process and main facilities. Moreover, after their application to Huobei 021 and Huobei 022 wells, it’s found that the technology of gas and/or mist drilling can increase a rate of penetration（ROP）, decrease a well deviation, and discover oil and gas layers more easily. At last, some suggestions are made, such as to strengthen an in-situ utilization and management of drilling tools, and to detect and change some failure tools in time.

In Yuanba continental areas with complicated geological conditions, some problems occur in drilling engineering, such as, great difficulties, various uncertainties, and high risk of well control. Therefore, how to optimize the casing program of a horizontal well with complicated geological conditions is very critical. Based on both the analysis on geological features and drilling difficulties and the real casing program of horizontal well, the key problem which may restrict the optimization has been found. Through a casing-program design of “inside-out” and “bottom-up”, a method including Ø139.7 mm of casing perforation completion and Ø152.4 mm of openhole completion formed, and was applied to 3 horizontal wells. Better application effect was obtained, the complicated accident rate reduced to 0.55 %, and the penetration rate and production efficiency increased by 113.95 % and 6.86 %, respectively.