Favorable Facies Research Articles

Characterization of subaerial lava flows of the presalt strata in the Santos Basin based on basic well logs

It is hard to identify volcanic morphologies using well logs to support technical decisions during well drilling and the acquisition of geological information. Therefore, this study was carried out on the volcanic sequence present in the Presalt interval of the Santos Basin, Brazil, which is referred to as the Camboriú Formation. This section was described in a previous study using image well logs as a succession of subaerial lava flows formed mainly by compound pahoehoes, sheet pahoehoes and rubbly pahoehoes. Based on sidewall core samples and petrophysical, geochemical and mineralogical reports, we identified five electrofacies from gamma ray, resistivity, sonic, density and neutron logs, representing patterns for identifying lava flows in subaerial sequences. In addition, we applied a porosity quantification method that resulted in a method for obtaining information from the matrix and presented coherent values in facies that did not present amygdalae or breccias and inferring altered zones from variations in resistivity and density logs or from cross-plots. Patterns of well log responses were defined for each type of lava flow present in the studied well, as was the inference about the most favorable facies for reservoirs. This methodology, which uses basic well logs from basalts, is unprecedented in the Presalt sequence and can be easily used to evaluate this exploratory frontier because of its close association with subaerial volcanism.

Discovery and inspiration of large- and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea: An example from Paleogene Enping Formation in Huizhou 26 subsag, Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin, the geochemical indexes of source rocks were measured, the reservoir development morphology was restored, the rocks and minerals were characterized microscopically, the measured trap sealing indexes were compared, the biomarker compounds of crude oil were extracted, the genesis of condensate gas was identified, and the reservoir-forming conditions were examined. On this basis, the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources, the development characteristics of large-scale high-quality conglomerate reservoirs, the trapping effectiveness of faults, the hydrocarbon migration and accumulation model, and the formation conditions and exploration targets of large- and medium-sized glutenite-rich oil and gas fields. The research results were obtained in four aspects. First, the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies, which have typical hydrocarbon expulsion characteristics of “great oil generation in the early stage and huge gas expulsion in the late stage”, providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation. Second, under the joint control of the steep slope zone and transition zone of the fault within the sag, the large-scale near-source glutenite reservoirs are highly heterogeneous, with the development scale dominated hierarchically by three factors (favorable facies zone, particle component, and microfracture). The (subaqueous) distributary channels near the fault system, with equal grains, a low mud content (<5%), and a high content of feldspar composition, are conducive to the development of sweet spot reservoirs. Third, the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation, and the NE and nearly EW faults obliquely to the principal stress have the best control on traps. Fourth, the spatiotemporal configuration of high-quality source rocks, fault transport/sealing, and glutenite reservoirs controls the degree of hydrocarbon enrichment. From top to bottom, three hydrocarbon accumulation units, i.e. low-fill zone, transition zone, and high-fill zone, are recognized. The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment. The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin, and present a major breakthrough in oil and gas exploration.

东营凹陷泥页岩有利相带定量评价

东营凹陷泥页岩有利相带定量评价

Depositional Model for the Early Triassic Braided River Delta and Controls on Oil Reservoirs in the Eastern Junggar Basin, Northwestern China

The Triassic Jiucaiyuan Formation is a vital oil and gas exploration target in the eastern part of the Junggar Basin. In this work, cores, thin sections, particle sizes, and conventional physical properties were analyzed in order to understand the sedimentary characteristics and depositional model of the Jiucaiyuan Formation in the Beisantai Uplift and to clarify the factors controlling reservoir development. The results demonstrate that the Jiucaiyuan Formation can be divided into seven lithofacies, namely massive bedding gravel, massive bedding sandstone, trough bedding sandstone, plane bedding sandstone, wavy bedding sandstone, parallel bedding siltstone, and massive bedding mudstone. Braided river delta facies dominate the Jiucaiyuan Formation. Nine main subtypes of facies were observed: flood plain, braided channel above lake level, natural levees above lake level, braided channel under lake level, interdistributary bays, natural levees under lake level, mouth bars, prodelta mud, and beach bar. The braided channel under lake level, mouth bar, and beach bar reservoirs exhibited the best physical properties, with average porosities of 16.54%, 19.83%, and 20.41%, respectively, and average permeabilities of 3.43 mD, 9.91 mD, and 12.98 mD, respectively. The physical properties of reservoirs in the study area are mainly controlled by sedimentation. Braided channels under lake level, mouth bars, and beach bars are favorable facies for the development of high-quality reservoirs. The results of this study are expected to serve as a theoretical basis for further exploration and development of oil and gas in the study area.

Lithofacies analysis and paleosedimentary evolution of Taiyuan Formation in Southern North China Basin

The Permian Taiyuan Formation contains alternate shale and coal lithologies which are vital for the exploration of shale gas reservoirs. However, previous studies have neglected the influence of paleosedimentary environment on the formation and distribution of marine-continental shale. A better understanding of the evolution characteristics of the paleosedimentary environment of the marine-continental strata is particularly critical to the accurate prediction of high-quality shale reservoirs. In this study, the geochemical and mineralogical characteristics of Taiyuan Formation, marine-continental strata in the Southern North China Basin, were carried out using lithology identification, element analysis, and X-ray diffraction analysis. These interpretations were helpful to develop a sedimentary depositional model by principles of sedimentology and sequence stratigraphy. The evolution of the paleosedimentary environment and the control of the paleosedimentary environment on the organic matter abundance, mineral composition, lithofacies, and gas enrichment of shale were analyzed. The results show that the vertical variation of the paleosedimentary environment had obvious stages during the Taiyuan Stage of the Early Permian. Based on sequence identification and division, a multi-stage superimposed marine-continental sedimentary model of transgressive and regressive assemblages was established. From tidal flat facies to lagoon facies and then to restricted platform facies, the contents of felsic and clay minerals decreased, while the contents of TOC and carbonate minerals increased sequentially. The lithofacies types of limited platform shale and tidal flat shale were different and relatively single, while the lagoon contained the shale lithofacies types of the above two sedimentary microfacies due to its sedimentary microfacies development location. The lagoon facies shale of highstand system tract had high-quality paleo-productivity, and was distributed in a stretch on the plane and superimposed in multiple stages vertically of the basin, which could be selected as a favorable facies belt of marine-continental facies shale gas.

Application of Chemical Sequence Stratigraphy to the Prediction of Shale Gas Sweet Spots in the Wufeng and Lower Longmaxi Formations within the Upper Yangtze Region

Effective shale gas exploration is hindered by the need for obtaining high-resolution correlations between shale strata and the need for classifying shale facies. To address these issues, chemostratigraphy, sequence stratigraphy, and shale gas geology methods were integrated to develop a new method known as “chemical sequence stratigraphy,” which was successfully applied to the Wufeng–Lower Longmaxi Formations in the upper Yangtze region. Well Huadi 1 was used as a case study, and detailed data were acquired. Multivariate statistical analyses were applied to three defined indices having different genetic significance, namely: terrigenous input intensity (TII), authigenic precipitation intensity (API), and organic matter adsorption and reduction intensity (OARI). By analyzing the trends of these three indices, the Wufeng–Lower Longmaxi Formations were divided into five fourth-order chemical sequences (from bottom to top): LCW, MCL1-1, MCL1-2, MCL1-3, and MCL1-4. The geochemical facies were named and classified using the chemical sequence stratigraphic framework. The enrichment factor (EF) transformation of elements was conducted to determine whether an element is rich or deficient. The results showed that the favorable geochemical facies in the well were EF-Al deficient, EF-Ca rich, and EF-V rich. The organic matter content and rock brittle strength were then used as chemical parameters, and it was predicted that the LCW and MCL1-1 chemical sequences most likely comprised shale gas sweet spots. This conclusion is consistent with the drilling results and indicates that our proposed method is effective and reliable. This method is further applied to the Changning Shuanghe section, the Shizhu Liutang section, and sections in the Xindi 1 well in the upper Yangtze region. The comparative study of these four sections showed that LCW and MCL1-1 are the key chemical sequences for shale gas exploration and development in the Wufeng–Lower Longmaxi Formations within the Upper Yangtze region.

Control of the Cretaceous Paleofluid Potential on the Source-Distal Lithologic Reservoirs in the Western Tabei Area of the Tarim Basin

The Cretaceous clastic oil and gas reservoirs in the western Tabei area of the Tarim Basin are far away from source rocks (source-distal), and the hydrocarbons mainly originate from Triassic continental source rocks in the northern Kuqa Depression. Early exploration focused on structural oil and gas reservoirs, and yet, with deepening of exploration practice, exploration has shifted from structural oil and gas reservoirs to lithologic reservoirs. In such context, under guidance of the theory of migration and accumulation for source-distal reservoirs, the key accumulation period of Triassic source rocks is determined, and the migration path of oil and gas is clarified. According to the geological characteristics of the study area, the impression method and sequence ratio method are used to restore the paleoburial depth, and the Fillippone formula is used to restore the paleopressure. Based on Hubbert’s theory, the paleofluid potential field of Triassic oil and gas in the Neogene Kangcun period is reasonably reconstructed. These combined with the planar structural evolution of Cretaceous reveal the preferential source-distal migration paths and directions of oil and gas. The favorable area of oil and gas accumulation is demarcated, and then, the facies belts with favorable lithology have been identified. The research results show the following: (1) The hydrocarbons of the Cretaceous oil and gas reservoirs originate from the Triassic source rocks. The Neogene Kangcun period is the key accumulation period. Hydrocarbons migrate to the western Tabei area along the Cretaceous basal unconformities and Late Yanshanian faults. (2) The paleofluid potential field of the Cretaceous during the key accumulation period shows the characteristics of “being high in the north and low in the south,” which is consistent with the gradual decrease of fluid potential along the migration distance from the northern hydrocarbon generation center (Kuqa Depression) to the south slope, and coincides with the main distribution range of source rocks in the Kuqa Depression. On the basis of the aforementioned, four preferential source-distal migration paths and directions of hydrocarbons have been clarified, and the Yudong-Yingmaili area is confirmed as a favorable area for the source-distal migration and accumulation of hydrocarbons into the Cretaceous. (3) In terms of the favorable areas for source-distal oil and gas migration and accumulation to Cretaceous strata, the forward distal end and lateral flanks of the branched retrogradational delta are the favorable facies belts for the next exploration of lithologic oil and gas resources. The recent breakthroughs in the lithologic reservoirs of wells D7 and M46 have confirmed that the findings of this research on the preferential source-distal migration paths and accumulation positions of hydrocarbons are of great guiding values for exploration deployment of Cretaceous lithologic reservoirs far away from source rocks.

Seismic prediction of oolitic beach thin-bed reservoir based on favorable facies belt constraints: Taking the second member of Feixianguan Formation in Jiulongshan area, Northwest Sichuan, China

The second member of Triassic Feixianguan Formation in Jiulongshan area of northwestern Sichuan Basin has made breakthroughs in natural gas exploration and has great exploration potential. Drilling data show that the second section of Feixianguan Formation has developed multiple sets of reservoirs, which are mainly concentrated in the upper sub-member of the second member of Feixianguan Formation. The overall heterogeneity is strong, the lithology and physical properties are complex and changeable, the reservoir thickness is thin, and drilling is less, so it is difficult to determine the spatial distribution characteristics of oolitic beach reservoir, which restricts the natural gas exploration process in this area. For the oolitic beach reservoir in the upper sub-member of the second member of Feixianguan Formation of Jiulongshan area, using downhole reservoir characteristics and 3D seismic data, the reflection characteristics of oolitic beach reservoir are analyzed, and then the seismic response model of oolitic beach reservoir is established by forward modeling. It is clear that the seismic response characteristics of the reservoir in this area are weak amplitude-continuous reflection; through the use of layer flattening impression method to restore the ancient landscape of the second section of Feixianguan Formation, combined with seismic facies analysis and seismic amplitude attribute characteristics, The distribution characteristics of favorable facies belt for oolitic beach development are determined. Based on the distribution of favorable facies belt, this paper uses the relative impedance-based tuning amplitude inversion and waveform difference inversion method to make a fine prediction of the spatial distribution of the reservoir, defines the spatial distribution characteristics of the reservoir, and predicts the thickness and fracture development of oolitic beach reservoir. The prediction results of the reservoir thickness are in good agreement with the actual drilling results, which confirms the application of this prediction method in this area. According to the fracture development, wave impedance value less than 1.6×106 g/(cm2·s), reservoir thickness, and other indicators, the favorable development area of oolitic beach reservoir is further delineated, which provides a favorable basis for the next exploration and development.

An integrated pore size distribution measurement method of small angle neutron scattering and mercury intrusion capillary pressure

Small-angle neutron scattering and high-pressure mercury intrusion capillary pressure testing are integrated to analyze the pore size distribution of the broad sense shale oil reservoir samples of the Permian Lucaogou Formation in the Jimsar Sag, Junggar Basin, China. The results show that, compared with the measurement method integrating gas adsorption and mercury intrusion, combination of small-angle neutron scattering and mercury intrusion can more accurately characterize full-scale pore size distribution. The full-scale pore size distribution curve of the rock samples in the study area includes two types: the declining type and submicron pore-dominated type. The declining type is mainly found with silty mudstone and dolomitic mudstone, and most of its pores are smaller than 80 nm. Silt-fine sandstones and dolarenite are mostly of the submicron pores-dominated type, with most pores smaller than 500 nm. They also present large specific pore volumes and average pore diameters of macropores and are the favorable lithogenous facies for development of high-quality reservoirs.

Sedimentary Evolution Characteristics of Fine-Grained Lithofacies under the High-Resolution Isochronous Shelf System: Insights from the Wufeng-Longmaxi Shales in the Sichuan Basin

Abstract The deposition and evolution of fine-grained sediments is a hot topic in fine-grained sedimentary rock studies and is important for accurately evaluating shale gas sweet spots. In this paper, the fine-grained deposition and evolution characteristics of the Wufeng-Longmaxi shales, major targets for Chinese shale gas exploration, were studied by using core observations, thin section analyses, scanning electron microscopy, geochemical analysis, and fossil identification. This work accurately identified six typical lithofacies; among them, the organic matter-rich siliceous shale facies (OMRSSF), the high-organic matter siliceous argillaceous shale facies (HOMSASF), and the medium-high organic matter low calcareous siliceous shale facies (M-HOMLCSASF) are favorable facies for shale gas exploration. The high-resolution isochronous unit in the shelf fine-grained sedimentary system was established, and the differential evolution of lithofacies in the system tract was discussed. The lithofacies deposition and differentiation in the transgressive system tract were controlled by the transgressive scale and tectonics under increasingly shallow water conditions. The lithofacies deposition and differentiation in the regressive system tract were controlled by tectonics and the preexisting lithofacies. The lithofacies in the regressive system tract had more frequent facies transitions and greater differentiation than those in the transgressive system tract, and they exhibited significant spatiotemporal inheritance. Sequential differential sedimentary sequences and symmetric differential sedimentary sequences were distinguished in the continental shelf sedimentary system. The lithofacies depocenters and subsidence centers were consistent in the transgressive system tract, while the tectonically active paleocontinent was important in the regression system tract. This study is of great significance for further high-resolution exploration of marine shale and improvement of the theory of shelf fine-grained sedimentary systems.

Depositional facies and diagenesis of the Lianglitage Formation in northwestern Tazhong Uplift, Tarim Basin, China: implications for the genesis of ultra-deep limestone reservoir

The limestone reservoir beds of Late Ordovician Lianglitage Formation are preserved in northwestern Tazhong Uplift of the Tarim Basin with buried depth exceeding 6000 m. The origin of the ultra-deep limestone reservoir is still controversial, which restricts the further hydrocarbon exploration. In order to clarify the main controlling factors of reservoirs, we carried out the study of sedimentary facies, diagenesis, and reservoir characteristics based on seismic, well logging, and core data. The Lianglitage Formation in northwestern Tazhong Uplift is mainly composed of nine lithofacies that are deposited from platform margin reef-shoal, platform-interior shoal, and restricted lagoon to tidal flat environments. The Lianglitage Formation has experienced syndepositional submarine diagenesis, penecontemporaneous diagenesis, and burial diagenesis, and consequently the reservoir space in the formation mainly includes fractures and dissolution vugs and caves. Reef and shoal deposits are the material basis of favorable reservoirs, and the favorable reservoirs have been mostly improved by the dissolution of meteoric water in penecontemporaneous diagenesis. In the burial stage, the early-formed porosity was destroyed by cementation to some extent, but the fractures and associated vugs formed in the late Ordovician and Silurian-Devonian played an important role in the improvement of the reservoir. The results are of great significance to the prediction of deep carbonate reservoirs and the hydrocarbon exploration in basins of western China. Favorable facies, early-stage improvement by meteoric water, and tectonic fracture are key to the formation of high-quality large-scale deep limestone reservoirs.

Fine-grained rock fabric facies classification and its control on shale oil accumulation: a case study from the Paleogene Kong 2 Member, Bohai Bay Basin

Lacustrine shale oil resources in China are abundant, with remarkable exploration breakthroughs being achieved. Compared to marine shale oil in North America, efficient exploration of lacustrine shale oil is more difficult; thus, selecting favorable layer and optimization zone for horizontal wells is more important. In this study, based on systematic coring of approximately 500 m fine-grained deposits of the Kong 2 Member, combining laboratory tests and log data, source rock geochemistry and reservoir physical properties, the favorable rock fabric facies for oil accumulation was analyzed and classified. First, the dominant lithologic facies, organic facies, and bed combination facies were determined based on mineral composition from logging, total organic content (TOC), and sedimentary structure. Secondly, 10 fabric facies were classified by combining these three facies, with 4 fabric facies were found to have high TOC content, high total hydrocarbon, and strong fluorescence features, indicating good shale oil enrichment. Thirdly, the distribution of the upon good fabric facies was identified to be located at the top of the Kong 2 Member, with evidences of seismic resistivity inversion, thermal maturity, structure depth, and strata thickness. And the favorable facies were found to be stably distributed lateral at the area of about 100 km2. High oil flow has been detected at this layer within this area by several wells, including horizontal wells. The exploratory study of fabric facies classification and evaluation provides a new research idea for lacustrine shale oil exploration and effectively promotes breakthroughs in lacustrine shale oil exploration in Bohai Bay Basin.

Using characteristics of pressure-temperature induced permeability variation of typical carbonate rock to determine its performance as reservoir or cap rock

The current research on carbonate rock often focuses on the storage space for oil and gas, and exploration of carbonate rock in petroliferous basins also mainly searches for high-quality reservoir rock for hydrocarbons. However, the importance of effective carbonate reservoir-cap rock configuration is increasingly highlighted, as hydrocarbon exploration advances towards deeper and older strata. Exploration practice shows that the favorable facies belt of carbonate rock, though deeply buried, still develops highly desirable reservoir rock with high porosity and permeability. Therefore, the presence of an effective carbonate cap rock collaborating with this reservoir rock becomes key to hydrocarbon exploration in deep carbonate rock. This research, for the first time, systematically and thoroughly carries out permeability measurement through the whole triaxial compression process of typical carbonate rock at varied temperatures, and captures the permeability evolution during deformation and failure, affected by temperatures and confining pressures. Test results show that typical dolomite and limestone present varied permeability variation characteristics in a triaxial loading state. Dolomite appears to be more of reservoir rock. It presents higher critical confining pressure for brittle–ductile transition, and is more prone to fracturing. Its permeability grows with temperature elevation. As for limestone, it has better performance as cap rock, which is embodied as the lower critical confining pressure for brittle–ductile transition, high sealing capacity, and permeability reduction with elevated temperatures. To sum up, vertical stacking of dolomite and limestone can form an effective reservoir-cap rock assemblage for hydrocarbon accumulation.

Effects of lacustrine depositional sequences on organic matter enrichment in the Chang 7 Shale, Ordos Basin, China

Chang 7 Shale, characterized by lacustrine black organic-rich shales and interbedded siltstones, has become a target for shale oil exploration and development in the Upper Triassic Ordos Basin, China. However, the heterogeneous enrichment of organic matter (OM) has led to controversy regarding source rock evaluation and difficulty in accurate prediction of favorable zones. Sequence stratigraphy, as a tool for prediction of sedimentary deposits has encountered challenges in lacustrine deep-water environments because of rapid facies changes and limited lateral continuity of key beds. In this study, a novel method is proposed to predict OM enrichment based on parasequences division and calibration of well logging and core lithology through analyses of thin sections and geochemical data from 238 core samples, as well as available well-logging data from a selected well. Chang 7 shales were simplified into three facies in terms of sedimentary structure and mineral composition, combining geological genesis with lateral correlation. Argillaceous laminated shale (Facies 2), with the highest average total organic carbon and S1 + S2 values, is the most favorable facies for shale oil exploration. The Chang 7 Member was divided into 15 parasequences and six parasequence sets, within one transgressive-regressive sequence. Depositional sequences have a significant effect on the enrichment of OM, given 1) the influence of lake-level fluctuations on OM accumulation, 2) the OM enrichment determined by shale facies, and 3) the distribution of shale facies controlled by parasequences. In particular, the most favorable locations are the bases of parasequences (generally the lower third to half from the bottom) in the TST and early RST. The application of this method to a test well showed excellent performance based on verification from the organic geochemical data of 86 samples. Five favorable targets of Facies 2 were marked within fifteen favorable locations. By linking meter-level depositional sequences with centimeter-level OM enrichment, this study provides an alternative approach to determine the target area in a single well profile and realize isochronous inter-well prediction for deep-water shales.

Enhanced and fine seismic recognition of organic reefs: a case study of the Changxing Formation, eastern Sichuan, China

Organic reefs are developed in the Changxing Formation (Fm.) in the southeastern end of the Kaijiang-Liangping ocean trough, eastern Sichuan. Due to the ambiguous seismic reflection characteristics of organic reefs, application of organic reef recognition methods that have been successfully employed in other areas is limited in the study area, but these methods can still indicate development of favorable facies zones. Accordingly, supplemented by seismic reflection characteristics analysis, seismic attributes analysis and time-difference analysis, frequency decomposition and reconstruction interpretation technique, high-frequency uncompressing method, and dominant azimuth lightening method were optimized to be the core technologies of enhanced and fine depiction technique system of organic reefs. The technique system transforms seismic data from the time and reflection angle domain to the frequency and azimuth-offset domain; increases the differences in seismic reflection characteristics in and out of organic reefs, especially patch reefs of small volume and low recognition; enhances seismic reflection characteristics of both the outline especially the lateral boundary and interior of organic reefs; and achieves precisely depicting the boundary of organic reefs and fine recognition of the internal structure of platform margin facies reefs such as reef core, fore reef, and back reef. This technique system provides a new technical idea for organic reef recognition, has produced optimistic recognition effects in the study area, and is of certain guidance significant to the research into recognition of organic reefs with ambiguous seismic reflection characteristics.

Application of VSP well drive data in the prediction of complex carbonate reservoirs

The qixia formation carbonate rocks in the northwest of sichuan are of great buried depth, thin reservoir thickness and strong heterogeneity. Therefore, VSP data are used to control the seismic data on the surface, VSP well drive data lay a good foundation for interpretation. Then, through waveform clustering analysis, favorable facies zones were developed. Secondly, natural faults are predicted based on maximum likelihood attribute technique. Finally, the reservoir quantitative prediction is carried out by using phase control inversion technique. The drilling well location is optimized based on reservoir and fracture prediction information, and the drilling effect is good, which provides strong technical support for subsequent exploration and development in this area.

Application of seismic sedimentology in predicating sedimentary microfacies and coalbed methane gas content

The identification of sedimentary facies and their lithological distribution characteristics is very important for exploration and development of coalbed methane (CBM). However, the thin interlayer that is common in coal-bearing formation, makes it difficult to predict the favorable facies zone of high frequency sequences based on the conventional methods. In this paper, a seismic sedimentology method was founded to reveal the sedimentary microfacies of high frequency sequences in the coal-bearing Shanxi Formation of the Zhongyu area in the central-western of the Qinshui Basin. The first step of this method is the selection of equal-scale stratal slices and extraction of seismic attributes, then several useable seismic attributes were optimized from all seismic attributes based on the relationship between the seismic attributes and net-to-gross ratios of several single-wells, and finally a model was established to depict the spatial distribution characteristics of sedimentary bodies. Results show that the sedimentary environment of SQ8 and SQ9 in Shanxi Formation is lower delta plain and the upper delta plain respectively. Moreover, the distribution characteristics of net-to-gross ratio across the study area were predicted based on the provided seismic sedimentology. Subsequently, the relationship between the net-to-gross ratio and CBM content of several sing-wells was used to predict the CBM gas content in the study area. The results show that the CBM gas content of No. 2 coal seam ranges from 5 to 20 m3/t, and it decreases with the increase of the net-to-gross ratio in SQ8 and SQ9. The relative error for the predicated gas content results ranges from −14.48% to 3.94%, indicating that the method is effective. Finally, based on the distribution of CBM gas content, the study area is divided into four types, in which the muddy sediment control area (Type IV, located in the central and eastern parts of the study area) is the most favorable for CBM preservation. This study provides a methodology to predict the sedimentary microfacies and CBM gas content in the coal-bearing strata, which extends the application of seismic sedimentology in coal and CBM geology.

Study of sedimentary characteristic in Denglouku formation, southern Songliao basin, Northeast China

Based on geological and geophysical data (e.g., core observation, well-logging curves, logging, analysis assay, and seismic data), the sedimentary facies, characteristics and distributions of the Lower Cretaceous Denglouku formation in the southeast uplift region of southern Songliao Basin are analyzed. The study shows that four types of sandbodies developed in Denglouku formation: alluvial fan, fan delta, braided river and braided river delta. In the early stage of the transition period named D1 period, the deposition is significantly controlled by the fault depression, resulting in rapid unloading of the sediments. Five large-scale divided fault-depressions and two small fault depressions have been developed. The ancient uplift at the periphery of the fault depression refers to the main development area of alluvial fan depositional system, Fan delta deposits are distributed around the fault depression, and the fan delta front extends into the lake. During D2 (the end of the transition period), several geological processes exist: (1) the alluvial fan, fan delta, braided river, braided river delta and lake sediments developed; (2) the unified sediment unloading area is formed. Taking the community of the floodplain and shore-shallow lake contact zone as a boundary, the western part of the boundary mainly developed alluvial fan and braided river sedimentary system from the provenance highland in the western and northern, the east part mainly developed lacustrine facies massively. With the debris sediments of provenance highland injected into the lake basin successively, it constituted retrograde fan deltas in different scales. Among them, the fan delta front and braided delta front subfacies are the main enrichment reservoirs for oil and gas, which is the favorable facies of oil and gas exploration in the Denglouku formation in the future.

Gas accumulation conditions and key technologies for exploration & development of Sinian and Cambrian gas reservoirs in Anyue gasfield

Exploration of the Sinian-Lower Paleozoic formations in the Sichuan Basin starts from the 1950s, and is tortuous and complex. To summarize the exploration experiences is of great significance of reference for exploration of oil and gas in deep carbonate rocks of the Sichuan Basin. Gas accumulation in the Anyue oversize gasfield is chiefly controlled by the Deyang-Anyue intra-platform rift and central Sichuan paleouplift. The intra-platform rift controls the scale hydrocarbon generation center and effective hydrocarbon plays. The Anyue gasfield is characterized by near-source hydrocarbon accumulation. The marginal zone of intra-platform rift and high part of the paleouplift control the scale distribution of favorable facies belts of reservoir development, and overlapped by paleokarstic reformation, the reservoirs are widely distributed. The intra-platform rift and paleouplift jointly control formation of the scale traps and hydrocarbon enrichment. Gas reservoir features and major controlling factors for hydrocarbon accumulation have some differences in the main play strata, such as Longwangmiao Formation, and Member 4 and Member 2 of Dengying Formation. The gas reservoir in the Longwangmiao Formation is a lithologic gas reservoir under the tectonic setting, and the inherited paleouplift is a key for reservoir formation and hydrocarbon accumulation. The gas reservoir in the Member 4 of Dengying Formation is mainly controlled by large structural-stratigraphic composite traps, and the gas reservoir in the Member 2 of Dengying Formation is the structural trap. Distribution of the large gasfields in the Dengying Formation is controlled by the intra-platform rift, near-source hydrocarbon-reservoir configuration controlled by the ancient erosion plane and stratigraphic sealing in the updip direction. For exploration and development of the Anyue gasfield, four series of technologies are developed, namely, reservoir seismic fine description technology, well logging fine evaluation technology of gas layers, fast drilling technology of complex strata, and stimulation technology for high temperature and high pressure gas layers. Technical progresses provide powerful guarantee for efficient exploration and development of the oversize gasfields.

Types, distribution and play targets of Lower Cretaceous tight oil in Jiuquan Basin, NW China

Abstract Based on drilling and laboratory data, the formation conditions of tight oil reservoirs in the Jiuquan basin were comprehensively analyzed and the exploration domains were sorted out. The Jiuquan basin underwent three cycles of lake level fluctuation in early Cretaceous, leaving three sets of high-quality source rocks, the Zhonggou, Xiagou and Chijinbao Formations in the Lower Cretaceous. There are two types of reservoir assemblages, source-reservoir in one type and source below reservoir type, and two types of tight reservoirs, argillaceous dolomite and conglomerate. The “sweet spots” control the enrichment of oil and gas. Argillaceous dolomite tight oil reservoirs have the characteristic of “integrated source-reservoir”, with fractures connecting the matrix micro-pores, pore-fracture type and fracture-pore type “sweet spots” distributed in large scale. The sandy conglomerate tight oil reservoirs were formed by source-reservoir lateral connection, and can be divided into source below reservoir type, source-reservoir side by side type and “sandwich” type. The overlapping areas of the favorable facies belts of fan-delta front and the secondary pore developing belts are the “sweet spot” sites. The favorable areas for seeking conglomerate tight oil are fan-delta front deposits around the Qingxi, Ying'er and Huahai sags, with an exploration area of 550 km2; while the area to seek argillaceous dolomite tight oil is the NW fracture developed belt in Qingxi sag, with an exploration area of 100 km2.