The Lower Permian Shanxi Formation, Shiguhao area, Dongsheng gasfield, Ordos Basin, is a set of transitional sedimentary facies from braided river delta to braided river. And most sandbodies in this formation are characterized by fast lateral change and complicated vertical superimposition, so it is really hard to predict these sandbodies of thin bed and interbed. Existing drilling data reveal that Shanxi 1 gas reservoirs in some high-yield gas wells are closely related to sandbody pinchout. In order to accurately predict the distribution characteristics of channel sandbodies in the Shanxi 1 Member and deeply make clear the Shanxi 1 gas reservoirs, the channels of Shanxi Formation in Shiguhao area were identified according to some 3D seismic, drilling, and well-logging data, by means of two technologies of 90° phase transition and strata slice, 3D seismic interpretation advantage in lateral resolution, and theory of seismic sedimentology. Results show that (1) the technology of 90° phase transition is more accurate in identifying thin sandbodies. And when seismic-data volume processed by this technology is used to extract strata slice, both spatial distribution and boundary of channels can be depicted more precisely; and (2) drilling practices exhibit that several favorable zones of the Shanxi 1 gas reservoirs in Shiguhao area are located in the updip pinchout of channel sandbodies and the structural high. These gas reservoirs are of structural-lithologic compound ones. In conclusion, the method developed for fine channel identification based on seismic sedimentology may provide the foundation for fine description and development of gas reservoirs in this study area.

Most gas reservoirs of the Upper Sinian Dengying 4 Member, Gaoshiti block, Anyue gasfield, Sichuan Basin, are under the control of stratigraphic denudation pinchout, lithology, and structure. And they are large lithologic-stratigraphic compound trap reservoirs with high temperature and normal pressure under structural setting. In order to understand their characteristics and development performance laws and realize an efficient development, the performance monitoring was carried out for the Dengying 4 gas reservoirs in terms of well testing, well logging, and fluid analysis. Moreover, based on geological cognitions and development performance, not only the reservoir-fluid properties and distribution characteristics but also the reservoir-permeability pattern and development mode were presented. Results show that (1) the Dengying 4 gas reservoirs are featured by moderate content of both sulfur and carbon dioxide, and can be subdivided into Gaoshi 3, Gaoshi 2, and Gaoshi 9 reservoir-permeability zones; (2) in these gas reservoirs, there is no obvious edge and bottom water, the produced liquid in Gaoshi 1 well is from Dengying 2 Member, and some gas wells are contaminated at the bottomhole; (3) there are three reservoir-permeability patterns, including porous, vuggy, and fractured-vuggy types; and (4) it is reasonable to adjust a proration working system based on performance monitoring. In conclusion, the performance monitoring of all directions, and multiple angles, stages, and types is the effective means to understand the development characteristics and laws of large lithologic-stratigraphic compound trap reservoirs, and the method developed in this study can provide reference and guidance for the development of similar gas reservoirs.

In order to clarify the characteristics and influencing factors of produced liquid from the Middle Permian Shihezi 1 gas reservoirs, northern Daniudi gasfield, Ordos Basin, the occurrence state, production behaviors, and distribution laws of formation water in these gas reservoirs were taken as objectives. Furthermore, the effects of geological characteristics in liquid-producing wells, hydrocarbon-generating intensity, development of mudstone interbed, and local sandbody structure on the distribution of gas and water were analyzed. In addition, some factors affecting water-bearing gas reservoirs were pointed out. Results show that (1) the Shihezi 1 gas reservoirs in Daniudi gasfield belong to a sedimentary system of shallow low-energy braided river, their petrophysical properties are poor, and gas in the reservoirs is dominated by mixed gas and water; (2) the produced liquid is mainly free water and capillary water in pores. Based on production characteristics, the northern gasfield can be subdivided into three zones individually with low, moderate, and high liquid production; (3) the hydrocarbon-generating intensity controls distribution range of liquid-producing wells. In one area with stronger intensity, there is sufficient gas source supply which easily tends to get enriched; (4) inside these reservoirs, both mudstone interbed and shale content affect enrichment degree. The thick connected point-bar sandbodies with thin mudstone interbed, low shale content, good petrophysical property, and high porosity and permeability exhibit some characteristics of low liquid production; and (5) the effect of wholly regional structure on the gas-water distribution is not significant. However, inside the connected sandbodies at the same period, two features appear as the upper gas and the lower water, and the regional high is still one enrichment block. In conclusion, a lot of understandings on distribution characteristics of gas and water and their influencing factors can provide guidance for the development and adjustment of gasfields as well as the management of gas wells.

In order to clarify the development laws of Neogene Miocene and Palaeogene Oligocene reservoirs with high quality in Qiongdongnan Basin, promote their natural-gas exploration progress, and open up a new exploration prospect in deeper strata, both Yacheng and Baodao blocks in this basin were taken as objectives, the Miocene and Oligocene reservoirs in these two blocks were comparatively analyzed in some aspects of petrological and pore structure characteristics, and physical property by means of many data from core analysis, casting thin-section identification, scanning electron microscope (SEM), and mercury injection. And accordingly the main factors controlling reservoir development were determined. Results show that (1) in Yacheng block, the migration distance of sediment is shorter, so both compositional and structural maturities of the Miocene and Oligocene reservoirs are lower than those in Baodao block; (2) in Yacheng block, the reservoir space is mainly dominated by residual primary intergranular pore, and secondarily by secondary pore, e.g. dissolved pore and micro pore; (3) also in Yacheng block, the reservoirs are characterized by middle porosity, high permeability, thin throat, and homogeneity whereas these in Baodao block by middle-high porosity, low-middle permeability, fine throat, and heterogeneity; (4) with an increase of burial depth, the reservoir porosity and permeability in Yacheng block are on the decline; and (5) in Qiongdongnan Basin, sedimentary-facies belt is the predominant factor controlling physical property, and diagenesis is the key factor, in which compaction is one of the most important factors worsening reservoir property, formation overpressure plays a certain role in improving the property, and cementation and dissolution have limited effects on them.

In order to explore some distribution of sedimentary tuff in Upper Permian Wujiaping Formation, northwestern Sichuan Basin, its petrological characteristics, mineral composition, and electrical property were analyzed based on much data on mud logging, wireline logging, cuttings thin-section identification; and whole rock X-ray diffraction. Then, several basic characteristics of sedimentary-tuff reservoirs were summed up on the basis of other data on core physical property, scanning electron microscope (SEM), and wireline logging; Finally, the palaeogeomorphology before sedimentary-tuff deposition was reproduced by means of the residual thickness method, and the distribution characteristics of sedimentary tuff were determined. Results show that (1) the sedimentary tuff in Wujiaping Formation presents the electrical property characteristics of "two highs and one low"; (2) it is mainly developed in the central Wujiapiing Formation, SY1-1 well and west Longgang area. Large-scale volcanic eruption might happen during middle deposition of Wujiaping Formation to provide with abundant volcanic-ash source, whose distribution range is affected more by the palaeogeomorphology whereas thick sedimentary-tuff deposit may provide geomorphological condition for forming marginal platform shoal of Upper Wujiaping Formation in this area; and (3) the sedimentary tuff is always capable of better self-generation and self-storage, and some sedimentary-tuff reservoirs with high quality are mainly developed in this area. In conclusion, the research on sedimentary-tuff reservoirs is still in the early stage, and at present, it is a matter of the utmost urgency to strengthen some basic geological study and carry out systematical evaluation on reservoir property; In addition, both Middle Permian Maokou marginal platform shoal and Upper Permian Changxing bioreef reservoirs developed in the SY1-1 well and west Longgang area have favorable conditions for multi-layer stereoscopic exploration, so they are worth concerning.

For most shale-gas reservoirs of Upper Permian Longtan Formation, Qianbei coalfield, Guizhou Province, in order to evaluate their fracability, some gas-bearing property and organic geochemical characteristics of mud shale in JC-1 well were analyzed. Then, based on the analyzed gas-bearing property, this formation might be subdivided into four intervals from below. A lot of organic-rich mud shale samples from these intervals were analyzed from two aspects of whole-rock mineral compositional and rock mechanical characteristics, and their fracability was evaluated. Results show that (1) in JC-1well, both gas show and total organic content (TOC) of mud shale are higher, and the best TOC and gas-bearing property occur in the first interval; (2) from view of mineral composition, Longtan reservoirs are mainly composed of quartz and clay mineral, and secondarily carbonate mineral and a certain amount of siderite and pyrite; (3) these reservoirs are featured by compressive strength of 12.40~60.20 MPa, tensile strength of 1.21~6.07 MPa, Young's modulus of (18.90~31.30)×10³ MPa, and Poisson's ratio of 0.19~0.28; and (4) the mineral brittleness index is the highest in the first interval with 56.84 % on average, the lowest in the second one with 32.89 % on average, and lower in the third interval with 41.09 % on average. Moreover, the clay mineral content is high in the second interval. For all mud shale samples from whole length, the brittleness index calculated from the elastic parameter method ranges from 44.73 % to 66.30 %, averaging 53.16 %, and there is no obvious difference among these four intervals. For the first interval, its thickness laterally varies less and distributes stably. In conclusion, the Longtan Formation has greater development potential, in which the first interval developed by stably lateral distribution of organic-rich rocks with great thickness, is also the best shale-gas reservoirs owing to good gas show, high TOC and rock brittleness, low tensile strength, and strong fracability favorable for fracturing stimulation.

As a large offshore one in Yinggehai Basin, M gasfield has little drilling data but high-quality seismic data. In order to understand the sedimentary characteristics and evolutional modes in this area and adjust a few traditional research concepts on sedimentary facies, this study took I gas-bearing formation in this field as an objective to carry out fine analysis on core, well, seismic, and sedimentation based on high-quality seismic data. Then, combined with existing drilling and production data, one idea integrating seismic facies, sedimentary facies with production performance was established. Finally, the sedimentary-facies characteristics were described, the sedimentary evolution was illustrated systematically, and the field adjustment was successfully implemented, so as to provide reference and guidance for the later development. Results show that (1) there are four types of seismic facies identified in I formation, Member 2 of Yinggehai Formation. High-amplitude parallel one represents good physical property and corresponds to the deposit of primary shoreface beach bar facies, which is the predominant sweet spot reservoirs. And both migration-type and fill-type ones are featured by large thickness and poor physical property, corresponding to the residual beach bar sandbody reworked by gravity flow channel. And combined with production performance, these types of reservoirs with migration-type and fill-type seismic facies are proved to be of poor productivity; and (2) the sedimentary microfacies is littoral-neritic sedimentation reworked by water channel, and the reworked area is located to the west of 7 wellblock. In 5 and 9 wellblocks, the deposit of primary beach bar are basically preserved, the water channel is developed along NW-SE direction, and the thickness of deposit is spatially distributed in the shape of bead.

In Jin 58 wellblock, Dongsheng gasfield of Ordos Basin, in order to clarify the gas-water distribution in tight sandstone gas reservoirs of Lower Permian Lower Shihezi Formation and its influencing factors, some chemical characteristics and occurrence states of formation water in these reservoirs were analyzed based on their geological characteristics. Results show that (1) the formation water is one type of chloride calcium with high salinity, and its geochemical parameters reflect better sealing conditions favorable for gas accumulation and preservation; (2) it may be classified into three types, i.e., edge/bottom water, lens-shaped waterbody, and detained water; and (3) gas/water layer or gas-bearing water layer are areally dominant and multiple gas-water systems coexist vertically without a united gas-water interface. In conclusion, the gas-water relation is mainly under the joint control of hydrocarbon-generating intensity, reservoir connectivity and heterogeneity, and local structure, in which better the reservoir connectivity, more favorable for gas accumulation, otherwise the lens-shaped waterbody tends to form. Heterogeneity leads to the superimposed distribution of "gas layer-dry layer-water layer" in the vertical profile. Some local structures such as microfault and microfracture are not only the favorable migration pathway but also the main way to communicate waterbody with some other layers through reservoir reform whereas others including high point and uplift belong to certain belts relatively rich in natural gas.

Great achievements of oil and gas exploration in Beibuwan Basin have been made, but several difficulties to expand these achievements are further increasing. In order to clarify genetic mechanisms of inversion structure belt in eastern Wushi sag, and to provide guidance for exploration in northern South China Sea, this study took one uplift belt in Wushi sag as an objective to analyze its structural characteristics and forming mechanisms by virtue of structural physical simulation. And it's indicated that: (1) during late Oligocene, the eastern Wushi sag had some characteristics of "scissors-type opening-closing" tectonics, i.e., compression in the east and tension in the west. Many experimental results well reproduce the genetic mechanisms of these tectonics with simultaneous tension and compression under unified structural settings. Also during late Oligocene, two sets of "scissors-type opening-closing" tectonics which were tensile on one side and compressive on anther side were formed at the inversion structure belt; (2) on the whole, two structural deformation zones were developed on both sides with a wide and gentle anticline formed under compression in the northeast as an axis, and they are both tensile in the west and compressive in the east; (3) faulting got stronger and its extension became larger as these structural deformation zones extended to the west. In conclusion, a conjugate fault and rotation of its isolated fault block under regional compression stress in eastern Wushi sag are the genesis-dominating style difference of opening-closing tectonics. Due to a cutting effect of preexisting basement fault, this kind of mass rotation is common during falling of southern Beibuwan Basin, and it's right correspondent with compression in the west and tension in the east of Maichen sag.

Most gas reservoirs of Lower Permian Shanxi 1 Member is the principal target in Longdong area, Ordos Basin. In order to investigate four characteristics including lithological, electric, physical, and gas-bearing properties (so-called four-property characteristic) of Shan 1 reservoirs, clarify a four-property relationship, deepen geological understanding, determine the minimum effective thickness, provide basis for optimizing test intervals and reservoir-reforming parameters, and further increase an development effect, this paper took core analysis data, core porosity and permeability, and well-logging parameters as objectives to analyze their four-property characteristics by means of two methods of both porosity-permeability crossplot and multiple regression, core observation, thin-section identification, high-pressure mercury injection, sealed coring, and NMR experiments. In addition, the relationship among four-property characteristics were presented. Results show that these gas-bearing reservoirs of Shan 1 Member are lithologically composed of quartz sandstone and lithic quartz sandstone; the lower limits of electric parameters are individually resistivity 30 Ω·m, interval transit time 206 μs/m, density 2.59 g/cm³, and shale content 15%; and the lower limits of physical properties are permeability 0.36 mD, porosity 4.1%, and gas saturation 46%, respectively. It's concluded that (1) Shan 1 Member may be classified as typical tight sandstone reservoirs because sandstone is featured by poorer physical property; (2) the four-property characteristics are correlative, and lithological one are the essential of "four-property" characteristics and dominates other three ones; (3) several established interpretation models of porosity, permeability, and gas-saturation are verified respectively, showing that they are of high precision and reasonable valuing; (4) some results from gas test are predicted by the determined minimum effective thickness and compared with actual ones, and their verification illustrates a high coincidence rate enough to meet a development demand; and (5) at present, gas development in Longdong area is still in an initial stage, and the lower limits of physical properties have an important influence on determining reservoir-reforming parameters, so they should be adjusted and optimized in time according to development progress.

Around Yacheng uplift, Qiongdongnan Basin, little exploration progress has been made for many years since discovery of both Yancheng 13-4 and 13-6 gas reservoirs; furthermore, for Sanya 1 Member in this uplift, the reservoir-forming characteristics, hydrocarbon migration and accumulation laws have not been figured out. So, it's necessary to carry out a systematic study. The reservoir type, and reservoir-forming characteristics and patterns of this member were explored on the basis of drilling and 3D seismic data, and other geochemical analysis and thin-section identification. In addition, several favorable exploration directions were pointed out. Results show that (1) in Yacheng uplift, Sanya 1 gas reservoirs belong to draped anticline and fault-lithologic ones, and gas is mainly generated from marine-continent-alternating facies source rocks of Yacheng Formation, Yanan sag; (2) gas migrates vertically to deltaic sandstone in Sanya 1 Member at shallower Yacheng uplift via NW-striking source connecting an active fault, and then laterally to higher position in the north; and (3) the predominant gas migration pathway is jointly affected by structural ridge settings formed by NW-striking faulting, muddy channel of Meishan Formation, and cutting relationship of Sanya 1 deltaic sandstone. And reservoir-forming patterns are featured by "vertical migration along No.3-1 fault, lateral migration and accumulation along fault ridge, cutting and sealing of muddy channel, and joint control of structure and lithology". In conclusion, the following oil and gas exploration in Yacheng uplift should focus on ascertaining the regional predominant oil and gas migration pathway. The reservoir-forming probability is higher in some low-amplitude anticlines on the migration pathway along the fault ridge, faulted nose structure, and lithologic traps laterally sealed by muddy channels.

In order to figure out one relationship of sulfur and ash content in coal to coal-forming settings, this study took some main minable seams in Guantianba syncline, Jinsha county, Guizhou Province, as objectives to analyze coal parameter characteristics. In addition, some difference of coal-forming sedimentary settings in different coal seams of Longtan Formation in this area was pointed out. Results show that (1) the coal seams of Longtan Formation are mostly featured by extra low total moisture, low to moderate ash content, moderate to high sulfur content, and extra low volatile, and they can be classified as No.3 anthracite coal (WY₃); (2) their sulfur composition is dominated by pyritic sulfur, representing a linear positive correlation with total sulfur content. The oxides of invariable elements in coal ash including mainly SiO₂, Fe₂O₃, and Al₂O₃. Compared with domestic coal average, an abundance of each element often presents slight enrichment; and (3) for different coal seams, their average total sulfur content and (Fe₂O₃+CaO+MgO)/(Al₂O₃+SiO₂) average ash content present a vertical variation trend of decreasing first and then increasing. It's indicated that not only No.4 but also No.5 coals in this area are formed by carbonaceous swamp of tidal flat facies less affected by sea water whereas No.9, No.13, and No.15 coals are carbonaceous swamp of lagoon facies strongly affected by sea water.

In order to make clear physical property, origins of low-permeability reservoirs, and favorable reservoir distribution, as well as to provide geological basis for comprehensive evaluating later hydrocarbon accumulation and optimal selecting potential exploration and development targets, this study took Lingshui Formation, Baodao area, Qiongdongnan Basin, as an example, and systematically analyzed the petrology, physical property, reservoir space characteristics, and the main factors affecting physical property by means of some data on well logging, cast thin section, SEM observation, clay X-ray diffraction. And accordingly, several favorable reservoir development belts of Lingshui Formation were defined. Results show that (1) two depositional systems of deltaic and littoral-neritic marine are mainly developed in Lingshui reservoirs, which are dominated by lithic quartz sandstone and feldspathic litharenite. Sandstone grains are mainly in the shape of round and sub-round and contact chiefly in the form of point and line, with the characteristics of medium- to low-texture maturity; (2) Linshui reservoirs are of medium to low porosity and low permeability, and their space is dominated by intergranular and intragranular dissolved pore and secondarily by intercrystalline dissolved pore, moldic pore, and matrix micropore; (3) sedimentation is one of the main factors controlling physical property. Favorable reservoirs are developed in the underwater distributary channel and mouth bar microfacies of deltaic front facies and in the shoreface sand bar and shoal microfacies of littoral facies; (4) both compaction and local high-calcitic cementation may make the physical property get worse but to some extent denudation may improve the physical property; and (5) located in the underwater distributary channel microfacies and in the shoreface sand bar microfacies, B3-8 and B3-6 zones are the most favorable for reservoir development, and more favorable for BX-1E zone located in the mouth bar microfacie.

For most fractured-vuggy karst gas reservoirs of Maokou Formation, southern Sichuan Basin, in order to further make clear reservoir-forming conditions and main controlling factors, and to search for fracture and vug systems developed extensively in karst, this study took the Lower Permian Maokou Formation in this basin as an example to comprehensively analyze its characteristics and factors controlling fractured-vuggy karst reservoirs according to field outcrop observation, and drilling and seismic data. Then, the typical Maokou fractured-vuggy gas reservoirs were presented. Finally, many factors affecting hydrocarbon accumulation and four enrichment modes were summarized. Results show that (1) deposits of high-energy bioclastic beach facies developed widely in southern Sichuan Basin during the sedimentation of Maokou Formation may provide material base for karst reservoirs. And later karstification is the key to forming these fractured-vuggy karst reservoirs; and (2) hydrocarbon accumulation, and enrichment and high yield are jointly affected by source fault and massive faults. And there are four enrichment modes, including the karst fracture and vug enriched body of faulted anticline, the karst fracture and vug enriched body of faulted buried high, the karst fracture and vug enriched body of interlayer fault, and the karst fracture and vug enriched body of faulted syncline.

Based on previous results, combined with geophysical data, this study analyzed Leikoupo 3 Member, Lianhuashan area, southwestern Sichuan Basin, from aspects of sedimentary facies, reservoir characteristics, and source-reservoir assembly by means of field outcrop observation, core description, and thin-section analysis in order to strengthen an exploration prospective of Leikoupo Formation. Results show that (1) during the sedimentation of Leikoupo Formation influenced by not only alternative and sharp rise of surrounding paleo-continent but also submarine uplift, the southwestern Sichuan Basin was in the closed and semi-closed state and the water energy was limited. Leikou 3 Member is characterized by higher water energy and developed grain beach, and composed of arenite and algal dolomites. Its reservoir space is dominated by dissolved pore and intercrystalline dissolved pore, and its property is good. Locally developed microfactures may provide better pathway for gas migration and accumulation; (2) there is a large area controlled by structure conducive for hydrocarbon accumulation. Developed faults are favorable for gas generated in the footwall Xujiahe 1 Member then lateral migrating to the hanging-wall Leikoupo 3 Member to accumulate there; and (3) gypsums in the overlying Leikoupo 4 Member may provide good caprock conditions for gas accumulating in Leikoupo 3 Member. In conclusion, owing to large thickness, good source-reservoir assembly, advantageous reservoir-forming conditions, and abundant controllable resources, Leikoupo 3 reservoirs in Lianhuashan area should be a favorable belt for exploration and development of Leikoupo Formation in southwestern Sichuan Basin.

Previous study deems that Peng 2 gas reservoirs of Xinchang gasfield, West Sichuan Depression, Sichuan Basin, are relatively homogeneous and better in physical property. As their development advances continuously, however, several dynamic characteristics presented during well testing and production test are different from ones ever realized. In order to deepen more studies on the physical property and further improve the geological understandings on gas reservoirs and their development effect in middle to later stages, this paper took the matrix and fracture permeability measured from some test with overburden pressure as examples to analyze the distribution characteristics of matrix permeability under overburden pressure. And then, the heterogeneity of matrix and fracture permeability was pointed out. Results show that, (1) on the whole, Peng 2 gas reservoirs shall be included in the category of tight instead of low-permeability reservoirs. The permeability distribution is obviously different in different horizons. The matrix permeability under formation conditions is of stronger heterogeneity; and (2) fracturing-induced fractures may further intensify the heterogeneity whereas natural fractures play an important role in improving matrix permeability and transforming heterogeneity intensity. In conclusion, the permeability calibrated under overburden pressure can truly reflect the physical property, and many variation coefficients obtained from empirical formulas can accurately characterize the areal heterogeneity intensity of permeability. And the development of similar gas reservoirs shall be based on progressive evaluation and gradual understandings and be carried out in the zoned and staged pattern.

In order to make a demonstrative exploration breakthrough of coalbed methane (CBM) resources in coal-bearing basins, western Inner Mongolia, this paper took the principal coal bed of Heishan coalfield as an example to analyze its basic geologic conditions. Then, some standards to select and evaluate CBM resource areas in this field were formulated based on exploration norms. Results show that (1) the principal coal bed is thick and extensive. Its coal metamorphic degree is moderate, rock types are mainly bright coal and semi-bright coal, and vitrinite content is high, all presenting strong hydrocarbon-generating potential; (2) on the whole, it's in a hydrodynamic environment which is relatively detained. Both top and bottom coal bed is mainly composed of thick mudstone and siltstone with strong sealing capacity available for CBM accumulation and preservation; (3) the coal bed is generally 600~1000 m deep with better porosity and developed fracture systems, which is favorable for a cost-effective development; and (4) the position and range of plays and the favorable targets of CBM resources in Heishan coalfield are defined according to these evaluation standards. The predicted CBM resources and abundance are 810×10⁸ m³ and 0.98×10⁸ m³/km², individually. In conclusion, the key parameters of gas content, reservoir pressure, pressure gradient, gas saturation, and permeability can be measured further by deploying parameter wells in the selected target areas.

Many shale-gas exploration practices in southern Sichuan Basin reveal that natural fractures are the key factors affecting shale-gas exploration and development. So, it's quite important to predict natural fractures in shale-gas reservoirs. In order to provide better guidance for shale-gas development, some technologies and modeling to finely predict fractures in shale-gas reservoirs were summarized. These technologies were applied mainly from two aspects of both fine attribute interpretation of seismic ant cube and fine establishment of geological model. Moreover, a fine platform velocity field was established to transform seismic interpretation data volume in time domain into data volume in depth domain, and then a fine geological model of ant cube was built. These technologies have been applied to the Changning National Shale-gas Demonstration Area. Results show, (1) when structure-steer filtering processing is conducted on original seismic data, both signal-to-noise ratio and structural interpretation accuracy may be improved; (2) applying Likelihood attribute to ant tracking can optimize an accuracy to predict fractures so as to obtain fracture response with smaller magnitude; (3) most exploration practices also illustrate that a coincidence rate of fine fracture prediction is 80% on average; and (4) to finely predict natural fractures can provide an effective guidance for setting fracturing scale, procedure, process, and parameters, so as to improve both stimulation effect and single-well productivity.

Paleostructural evolution plays an important role in controlling oil and gas migration and accumulation. Most previous paleostructural restoration was generally carried out on the basis of some single-well or seismic data. However, there is a little single-well data with nonuniform distribution, resulting in the restored paleostructure only just reflecting the major paleostructural setting. Moreover, the seismic-data-based restoration is mainly according to vertical thickness of formation, bring about some false appearance of paleostructure tending to occur in certain areas with large formation dip. So, a new method of paleostructural restoration was put forward to depict morphological characteristics of paleostructure precisely. Results show that, (1) in the 3D seismic working area of Jiulongshan to Jian’ge, structural layers are gridded by means of fine 3D seismic interpretation, formation dip of each grid point and true formation thickness between neighboring layers are calculated, and paleostructure is restored on the basis of this thickness; and (2) the paleostructure restored by means of this new method may present the morphological characteristics more precisely and the multi-direction structural trail distribution more clearly. In conclusion, Jiulongshan structure was formed under the control of NE- and EW-trending compressive folds; there was a large, wide, and gentle paleouplift appearing in central Jian’ge area during the late Indosinian; and structural evolution characteristics in the study area are accordant with the major setting of structural development and evolution in western Sichuan Basin. Keywords: Paleostructural restoration; Gridding; Formation dip; True formation thickness; Jiulongshan structure

In order to make countermeasures against horizontal-well stimulation for Lower Permian Lower Shihezi Formation, Dongsheng gasfield, large amount of geophysical, well-logging, mud-logging, and assay data on Shihezi 1 Member were analyzed systematically. And accordingly, several characteristics of these Shihezi 1 reservoirs were pointed out, including structure, sedimentation, petrology, physical property, pore and throat, interbed, and gas layer superimposition. In addition, some countermeasures against horizontal-well stimulation for these reservoirs were made. Results show that, (1) developed with proximal alluvial fan-braided river deposits, these reservoirs are structurally simple, presenting a monoclinal structure high in the northeast and low in the southwest; (2) for these sandstone reservoirs with light gray coarse-moderate lithic and lithic quartz sandstone as soul, their physical property is poorer, secondary intergranular dissolution pore and primary intergranular pore are the main pore types, and moderate and small throats are dominant, so that Shihezi 1 reservoirs are featured by extra low porosity and super low permeability; (3) in this thick Shihezi 1 Member with developed sandbody, various sets of gas layers are vertical superimposed, two or three sets accounting to 65%, and some interbeds between gas layers are mainly argillaceous and physical property ones; and (4) based on one thickness of the interbed between the target layer of horizontal well and its neighboring gas layer, certain stimulation countermeasures are made. According to their design idea, long fracturing is applied to the interbeds with the thickness≥5-7 m to ensure fracture length and control fracturing scale, and layer-penetrating fracturing is adopted for the interbeds with the thickness<5-7 m to guarantee fracture height and to increase fracturing scale. In conclusion, these countermeasures of horizontal-well stimulation may increase the productivity and provide the basis for the efficient development of Shihezhi 1 Member, Lower Shihezi Formation, Dongsheng gasfield.

Recent exploration achievements indicate that there are abundant shale-gas resources in Silurian marine strata, Sichuan Basin. Moreover, a great number of industrial discoveries have been obtained in southern basin. Some drilling practice in eastern basin also shows that there is dark high-quality shale at the bottom Longmaxi Formation; and gas logging anomaly, well kick, gas influx, and well blowout are common, showing greater exploration and development potential. This study took 2D seismic data within the scope of PetroChina’s mining rights in eastern basin as a research object. Both shale-gas regional geological and geophysical response characteristics were analyzed. Then, the thickness of high-quality shale of Silurian Longmaxi Formation was depicted by means of seismic inversion. Finally, shale distribution characteristics and trend were pointed out. Results show that (1) these shale-gas reservoirs are not under the control of structural traps, but in close relationship with the burial depth of the bottom boundary of Upper Ordovician, the location and size of fault, and the thickness of high-quality shale; (2) in eastern basin, some areas with burial depth ranging from 1500 m to 4500 m, thickness of high-quality shale greater than or equal to 20 m, and distance from the major faults over 1.3 km are just regarded as favorable exploration ones, and these areas may provide the basis and lay the foundation for shale-gas industrial development in eastern Sichuan Basin. In conclusion, the high-quality shale in eastern and southern basin is more favorable with greater thickness, so 3D seismic and exploration wells shall be deployed in these areas.

Some breakthrough has been made in exploration and development of marine shale gas in the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation, Sichuan Basin. But, other studies on continental shale gas are poor. So, the shale reservoirs of Xujiahe 1, 3, and 4 members, Sichuan Basin, were taken as research objects. Some features about their mineral composition, lateral and vertical distribution, organic geochemistry, physical property, and preservation condition were analyzed. Then, shale-gas resources of Xujiahe Formation in the whole basin were estimated by means of volume method. And accordingly, it's pointed out that the continental shale gas of Xujiahe Formation, Sichuan Basin, has greater exploration and development potential. Moreover, results show that (1) the shale of Xujiahe Formation is distributed in a large area with great thickness, the thickest in one area of Yaan of western basin-Zitong of northern basin, and getting thinner to southeastern basin; (2) the shale with TOC higher or equal to 2.0% is distributed widely, covering an area of 12.7×10⁴ km², which accounts to 66% of whole basin; (3) in Xujiahe Formation, the shale porosity is mostly less than 3.3%, and its physical properties are overall worse than those of the Lower Silurian Longmaxi Formation; and (4) these shale-gas reservoirs of Xujiahe Formation are better preserved. In conclusion, the shale gas of Xujiahe Formation has greater potential with resource in place about 46.45188×10¹² m³, among which 15% , 27% and 58% are distributed in Xujiahe 1, 3, and 4 members, respectively. And this Xujiahe Formation is one of the principle potential strata for exploration and development of continental shale gas in China.

In order to clarify the characteristics and formation mechanisms of sandbodies in deltaic front-lacustrine sedimentary system and lay the foundation for comprehensive adjustment in the middle to late development stages, we took some data from well logging, mud logging, core analysis, and cast thin-section identification of the Upper Jurassic Suining Formation, Luodai gasfield, western Sichuan Depression, Sichuan Basin, as research objects. After analyzing sedimentary facies and diagenesis systematically, the distribution characteristics of effective sandbodies were depicted, and their formation mechanisms were figured out. Results show that (1) for these effective sandbodies, their regional sedimentary environment is prograding deltaic front. And due to hydrodynamic force, distributary channel changes frequently in plane. It changes fast laterally, and mudstone and sandstone alternate with each other frequently and vertically. Two sets of sandbodies are highly superimposed vertically and distributed in the shape of blanket. On the whole, it's NW-SE striking. Single sandbody is thinner, but its cumulative thickness is greater and the percentage of effective sandbodies is higher. (2) The formation of sandbody is controlled by sedimentary environment and reworked by diagenesis. (3) In some interaction areas of underwater distributary channel, mouth bar, and lake wave with stronger hydrodynamic action, sediments are of good sorting, rock particles are relatively coarse, and effective sandbodies are developed. (4) Compaction leads to a significant reduction of primary porosity. Both quartz overgrowth and calcite cementation result in a further reduction of pore space whereas an increase of rock tightness. And (5) dissolution of unstable minerals and partial debris may improve porosity and permeability. Mudstone-sandstone-alternating beds change greatly. Several sedimentary-facies change belts of distributary channel and mouth bar or distal bar are the most favorably diagenetic microfracture development areas. And diagenetic microfractures may bring about a further improvement of both reservoir and seepage capacity.

Based on previous study on microbial carbonates, we analyzed and summed up its origin and classification, and the relationship to oil and gas accumulation. Results show that（1）the formation of microbial carbonates includes two processes, the acquisition and cementation of detrital grains, and the precipitation of carbonate mineral generating from microbial metabolism;（2）microbial carbonates are dominantly by stromatolite, thrombolite, dendrolite, and leiolites. And the first twos are the main rocks which stromatolite is mainly found in intertidal and shallow subtidal zones whereas thrombolite in shallow subtidal zone and interbank sea, respectively; and（3）featured by better petrophysical properties, the microbial carbonates with organic matter may be served as source rock, which are originally composed of not only bacteria but also low-class bacteria and algae.

In Hechuan area, the Upper Triassic Xujiahe 2 reservoirs have huge resources of natural gas. However, the reservoirs are featured by deeper burial depth, strong compaction and dissolution, different interstitial materials blocking pore and throat, leading to much difficulty and high cost in their exploitation. After exploration and development practice and experimental study, it is all found that among the tight sandstone reservoirs of Xujiahe 2 Member, there are still other high-quality reservoirs which may obtain high-yield gas flow. So, it’s very significant to implement a study on these high-quality reservoirs under the current situation of low oil price. In this study, for those reservoirs of Xujiahe 2 Member with porosity and permeability individually more than 9 % and 0.09 mD, the reservoir space was analyzed by means of core observation, identification of casting thin section, and SEM. It is found that the reservoirs can be classified into four types, including primary porous one, secondary porous one, compound porous one, and fractured-porous one. In addition, the main factors influencing their formation are also presented.

It is important to analyze mechanism forming high-quality reservoirs for predicting a favorable belt. In this study, some main factors to control the development of high-quality clastic-rock reservoirs were summarized in terms of sedimentation, diagenesis, tectonism, formation temperature, abnormally high pressure, and hydrocarbon filling. Results show that (1) mineral composition with high hardness was conducive to preservation of primary pore, a kind of depositional structure with coarse grain and low matrix was not conducive to karstification but may easily generate better reservoirs; (2) weakly siliceous cementation, and dissolution of both chlorite rim with a certain thickness and carbonate cement formed in the early stage were favorable diagenesis; (3) tectonism generated fractures; (4) formation temperature might affect the reaction rate of fluid and rock, and the evolution of organic matter, further to affect the forming high-quality reservoirs; and (4) abnormally high pressure and hydrocarbon filling are the second important factors.

After our study on extra-deep, tight, and fractured sandstone reservoirs, it is found that, as not only the main migration pathway but also the important reservoir space, fractures are geological foundation to realize a high-yield for whole gas reservoirs. In Kuchen Depression, Keshen 8 gas reservoir is just a typical extra-deep, tight, and fractured sandstone gas reservoir; furthermore, its fracture development is strongly uncertainty and heterogeneity. So, for these fractures, to understand their development laws, to carry out numerical simulation, and to predict their space distribution may effectively guide an overall exploration and production. In this study area, the burial depth of reservoir is always over 5500 m, bringing about weak precise in seismic data. In addition, a method called ANSYS limited element analysis was adopted for these gas reservoirs. This method firstly simulates the distribution of paleo and current stress fields, secondly implements an assignment of critical fracture parameters under constraints of multiple factors including outcrop observation, drilling, well logging, and dynamic performance, thirdly carries out a numerical simulation of fractures, finally establishes a fracture model matching highly with actually tested data. It’s an effective method to study fractures in reservoirs.

Mixing deposition is a special one. Recently, scholars have published a lot of research reports. In this paper, integrated with previous achievements, we sum up its research process and development, and illustrate its classification, terming, origins, controlling factor, model, and geological significance. The earlier study targeted its presentational feature; at the early of 21 century, the main research aimed to the significance to depositional environment; and the recent process focuses on the geological significance. Our study shows that fracture should be essential condition to forming high-quality reservoirs, mixing deposits might become high-quality source rock, and accumulation inside or outside source was able to form reservoirs.

After an analysis on the main controlling factors to form Cambrian reservoirs in northern Sichuan Basin and surrounding areas, we not only made reservoir-forming and accumulation rules clear, but also proposed some favorable belts. It is deemed that (1) the Cambrian is dominantly a reservoir-forming assembly of both lower source and upper reservoir; and (2) vertical and lateral near source is the material basis for oil and gas accumulation, high-quality reservoirs in shallow shoal facies belt and grain shoal generated from superimposed karstification are the premise to form reservoirs at the early stage, lithological trap with paleostructure background is the guarantee during reservoir-forming period, and better preservation conditions is the key to oil and gas accumulation at the early stage and to adjusting this accumulation at the later stage. The Cambrian in Yuanba-Renhechang area of northern Sichuan Basin will become the favorable one for next exploration due to better reservoir-forming conditions and assembly.

There are abundant CBM resources in Panguan syncline, Guizhou Province. We carried out a study on the distribution of coal seam, the characteristics of coal rock, the gas property, and the distribution of CBM resources in northern part, west wing of the syncline. Moreover, the CBM resources were evaluated by volumetric method, and some occurrence factors were analyzed. Results show that (1) there are 58.08×10⁸m³ predictable CBM resources from shallow coal seams which the burial depth is above 1500 m; (2) the main factors influencing their occurrence contain geological structure, burial depth, sealing property of both top and bottom layers, and hydrogeological conditions; (3) burial depth is the most important factor, and it appears a positive correlation with gas content; and (4) the more important one is geological structure, showing that gas is controlled by syncline and fractures, and sealed faults may form better sealing conditions available for CBM accumulation.

In Dongying Formation, LD6-2 structure, there are a lot of sandstone reservoirs developed, which are characterized by high permeability and high porosity with a better exploration potential. And many wells have obtained higher tested deliverability. For these sandstone reservoirs of Dongying Formation, their diagenesis and characteristics were studied by means of observation of both polarization microscope and scanning electron microscope, identification of clay X-diffraction, and conventional core analysis. Results show that (1) they are mainly composed of medium- to coarse-grained lithic arkose and secondly arkoses; (2) they experienced compaction, cementation, and dissolution, among which compaction accompanying with the whole diagenetic process had an obvious reforming effect on primary pore, making petrophysical properties poorer; (3) both carbonate cement and authigenic clay minerals occupied pore space, also resulting in poor petrophysical properties; and (4) dissolution, especially feldspar dissolution might generate lots of secondary pores, which might contribute to improving these properties.

For a reservoir, the four characteristics (including lithology, petrophysical property, gas property, and electric property) and their relationship are important for water and gas identification and reservoir evaluation. In this study, based on core observation, cutting mud logging, and thin-section identification, we analyzed the four characteristics of the reef shoal reservoirs of Changxing Formation, Yuanba area. Moreover, the relationship among these four characteristics was gained by means of conventional well logging, special well logging, and crossplot. Results show that (1) these reservoirs belong to reef shoal ones, which are composed of dolomite with dissolved pore, bioclastic powder- to fine-crystalline dolomite, residual bioclastic dolomite, bioreef dolomite; (2) with III-type as the soul, they belong to porous, and fractured-porous reservoirs with porosity ranging from 0.53% to 24.65% and 4.08% on average; (3) there is big difference existing in gas property, totally it in reef reservoirs better than that in shoal reservoirs, and shoal area in eastern part better than that in western part; (3) lithology has an obvious effect on petrophysical property, and dolomite reservoirs have better petrophysical property; (4) while gas found in reservoirs, resistivity is relatively low value under high resistivity value whereas resistivity is low value when water found. In general, better gas property leads to higher resistivity. However, the highest resistivity is affected by lithology not reacts to gas property.

Zhongba gasfield, discovered in 1972, has entered into the later development stage. It’s necessary to explore new replacement strata. So, based on previous study, the oil and gas geological conditions of Xujiahe 3 Member were analyzed. Results show that (1) there are two kinds of gas reservoirs including shale-gas ones and tight sandstone gas ones; (2) for the shale-gas reservoirs, the effective shale is featured by large thickness, stable distribution, and big gas-generating capacity; and (3) for the tight sandstone gas reservoirs, which are composed of underwater ditributary channel, mouth bar sandbody, and reservoir sandbody with the assembly of intercrystalline pore, dissolution pore and fracture as the reservoir space, they connect with large-scale source rock and belong to self-generating and self-preserving ones. Furthermore, part oil and gas generated from Xujiahe 1 Member migrated vertically to Xujiahe 3 Member. Our study demonstrates that in Zhongba area, the Xujiahe 3 Member has the better association of source, reservoir, and caprock; and there is a plenty of source rock with large exploration potential. So, this member should be another important exploration stratum since Xujiahe 2 Member and Leikoupo 3 Member.

Whether an area is suitable for a scale development or not depends on not only its geologic conditions to form shale-gas reservoirs but also economic feasibility of these reservoirs. In Dingshan area with favorable facies belt, there is high-quality shale with large thickness and stable distribution. Furthermore, the shale has well-developed reservoir space and better petrophysical property. In addition, with high gas-bearing content, it is characterized by fine brittleness and preservation conditions. In this study, according to different burial depth and combining to various initial production, we developed an economic map through Monte Carlo simulation. It is deemed that the probability with economic returns should be 91% when vertical section is 2000 m and initial production is 4×10⁴m³, 92 % for the vertical section of 3000 m and initial production of 5×10⁴m³, and 93 % for the vertical section of 4000 m and initial production of 6×10⁴m³, respectively. An analysis of past drilling also demonstrates that both increasing the production and decreasing the investment are important grasp to realize the economic feasibility. Furthermore, some measures about well trajectory control or length of horizontal segments and fracturing technology are made. Finally, we consider that, guided by the economic map, the scale development can be carried out for Dinshan area under current conditions of drilling engineering and techniques.

Sulige gasfield belongs to tight sandstone gas reservoirs with low permeability, porosity, and abundance. So far, low-to-moderate production wells which their yield is less than or equal to 0.5×10⁴m³/d take over 61.9 percent among vertical and cluster wells into production. However, there are two problems for the low-yield wells, including low productivity and wellbore liquid accumulation. For these kinds of wells, unreasonable production system and drainage measures, or not fishing the downhole throttler in time are not conducive to discharging liquid accumulation and increasing recovery. Furthermore, the cost of well production and management may be enlarged because of frequent intermittent switch on and off and huge water-drained volume. So, some measures are made for these wells with liquid accumulation, including fishing downhole throttler, optimizing drainage and recovery technology and management system. After the application of these measures, some wells with high pressure and low yield due to throttler or stopping producing because of liquid accumulation recovered a normal production. These drainage and recovery technologies also obtained an obvious stimulation effect, intermittent production system became more reasonable, average pressure different decreased very evidently, and liquid-drained effect was obvious. As a result, these technologies and measures to develop the low-yield wells gained an obvious improvement.

In Keshen block, Tarim Basin, most gas wells are featured by deep well depth, and high pressure and temperature. For these wells with high temperature and extra-high pressure, if annular pressure occurs abnormal, there is a huge risk existing in the follow-up production. Furthermore, other problems of both high cost and more operation difficulty also appear in a workover which may remove security risk. So, a risk assessment of abnormal annular pressure is presented to evaluate some risk in open and shut well. Meanwhile, many measures are made in order to ensure a safe production, containing supervision for some wells with controllable risk and workover for other ones with huge security risk.

There are some disadvantages in current restore production technologies used in Daniudi gasfield. So, four water-flooded wells were selected to carry out an experiment on wellhead liquid discharge and gas lift, and its economic effect was also evaluated. Results show that (1) these four wells obtain a successful restore production and success ratio achieves 100 %; (2) for this wellhead liquid discharge and gas lift, the time-consuming for single well shorts by 3.5 h compared to multiple-well compound gas lift, showing a better effect to gas recovery; (3) after restore production, a daily production increases 19 642 m³, cumulative yield of 197.747 3×10⁴m³, cumulative effect of 255.09×10⁴ yuan, operation fee for single well saving 5.77×10⁴yuan compared to nitrogen lift, input-output ratio of 1:277, all showing a better economic effect. So, the technology of wellhead liquid discharge and gas lift has a bright prospect in development of Daniudi gasfield.

Along with the development of Hubuzhai gasfield enters a later stage, and the problems of sand burial appear in most gas wells, which may lead to productivity decline and further influence a stable production. Many common-used sand-surface treatment technologies are unavailable to a good effect due to long sand-buried time, long length of sand-buried interval, impervious sand particle, and high compaction. So, an investigation was carried out on the basis of some successful experience from other foreign gasfields, a technology of nitrogen foam sand washing was optimized and used to be a tool for sand-surface treatment, and a method of snubbing process was presented to overcome defects in easy failure in wellhead BOP during a coiled-tubing sand washing. Meanwhile, an assembly of sand-washing rod string including drag bit, screw drill, and coiled tube was designed. Moreover, their application to Bu 1-X well shows that, due to operation time shorting about 37 % under the same sand-washing footage, both the snubbing process and the assembly of sand-washing are better than conventional hydraulic sand washing.

For Xujiahe 2 Member of Sumaotou structure, some previous research on the lower limit of petrophysical property was comparative rare, restricting the study of effective reservoir' distribution, and further resulting in little progress in the exploration of Xujiahe 2 reservoir. So, in this study, three methods of gas-water capillary pressure, relative permeability, and minimum pore throat radius were used to confirm the standards of lower limit. It is concluded, commercial gas is produced from Xujiahe 2 reservoir while the lower limit of porosity of 4.5%, corresponding to permeability of 0.0173 mD and the upper limit of water saturation of 45%. Natural gas is not obtained from this reservoir until the upper limit of water saturation increasing to 65%. The proposed lower limit may provide evidence for confirming effecting reservoirs in low and gentle structures.

Since PDC drilling causes cuttings finer, it is difficult to choose representative cuttings to divide strata by conventional mud-logging approaches. However, to use a method of element mud-logging is characterized by a little demand of samples, short time and complete data of analysis, and small error. Various elements can be found in deposits in different sedimentary environments. Therefore, data obtained from element mud logging can be adopted to confirm lithology, and divide strata by integrating some features of regional sedimentary facies.