Reservoir differences and formation mechanisms in the Ke-Bai overthrust belt,northwestern margin of the Junggar Basin,China

There are some differences in reservoir quality of clastic rock between the hanging wall and the foot wall of the Ke-Bai overthrust belt, northwestern margin of the Junggar Basin, western China, which affect the efficient petroleum exploration in this highly mature exploration area. Based on a large number of thin-sections, cast thin-sections, and physical property analysis of cores, we systematically discuss the Permian-Jurassic reservoir differences between the hanging wall and the foot wall of the Ke- Bai overthrust fault from the aspects of structural evolution, time-space distribution of the depositional system, diagenesis characteristics, and reservoir quality and analyzed the reasons for the differences in reservoir properties. The overthrusting of the Ke-Bai fault directly results in different burial histories, diagenesis evolution, and porosity evolution between the hanging wall and the foot wall. The diflbrences of reservoir characteristics are mainly embodied in buried depth, grain size, sedimentary facies, diagenetic stage, and reservoir quality. The analysis results showed that burial history and depositional characteristics controlled by overthrusting are direct influencing factors of reservoir differences. Because of shallow burial depth of the hanging wall, the reservoir compaction is weak and primary pores are preserved well. The porosity of reservoir on the hanging wall is generally 10%-25%. The strata on the foot wall are deeply buried, and there are mainly mixed pores with the average porosity of 5%-20%. The favorable reservoir on the foot wall is generally developed near faults or in the channel sand bodies, which are usually dissolution development areas.

Genesis of reservoir heterogeneity and its impacts on petroleum exploitation in beach-bar sandstone reservoirs:A case study from the Bohai Bay Basin,China

Reservoir characteristics of beach-bar sandstone reservoirs in the 2nd member of the Shahejie Formation in Banqiao Sag are studied by means of well logging interpretation,thin section observation and physical property analysis.Further,the influence of deposition,diagenesis and internal architecture interface on reservoir quality are quantitatively analyzed.On this basis,the geneses of reservoir heterogeneity of beach-bar sandstone reservoirs are summarized.The following results are obtained.(1)Primary pores,secondary pores and micro-fractures are the main types of reservoir space in the study area,and the primary intergranular pore is the main pore type;the microscopic heterogeneity of reservoirs is strong,and the physical properties of beach-bar reservoirs in different regions vary widely.(2)Tectonicdeposition,diagenesis and reservoir internal architecture work in unison to cause the heterogeneity of beach-bar reservoir quality in the 2^(nd) member of the Shahejie Formation in Banqiao Sag;the locations and scales of beach-bar sand bodies are obviously different in different fault blocks in the study area,determining the macroscopic distribution of beach-bar reservoirs;differential diagenesis intensifies the degree of reservoir heterogeneity;the fine-grained argillaceous deposits between different architecture units of beach-bar reservoirs are critical to the quality of reservoirs.(3)The differential distribution of beach-bar reservoir quality parameters in the study area affects the spatial heterogeneity of reservoirs,which not only controls the original oil/gas distribution,but also has a significant influence on the effect of waterflooding and leads to the local enrichment of remaining oil.

Distribution Patterns of Remaining Hydrocarbons Controlled by Reservoir Architecture of Distributary Channel with Different Channel Style: S2 Formation of Songliao Basin, China

1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et

A numerical investigation of gas flow behavior in two-layered coal seams considering interlayer interference and heterogeneity

Multiple-seam gas coproduction is a technology with potential to achieve economic targets.Physical experiments could replicate gas flow dynamics in two seams.In this study,numerical simulation was conducted based on physical experiments.Through calibration,the simulated results agreed with the experimental results.Three findings were obtained.First,the pressure distribution intrinsically depends on the depressurization effectiveness in each coal seam.The gas pressure difference and interval distance influence the pressure distribution by inhibiting depressurization in the top seams and bottom seams,respectively.Second,the production contribution shows a logarithmic relationship with the permeability ratio.The range of the production contribution difference grows from 11.24%to 99.99%when the permeability ratio increases 50 times.By comparison,reservoir pressure has a limited influence,with a maximum of 13.64%.Third,the interlayer interference of the top seams and bottom seams can be intensified by the reservoir pressure difference and the interval distance,respectively.The proposed model has been calibrated and verified and can be directly applied to engineering,serving as a reference for reservoir combination optimization.In summary,coal seams with a permeability ratio within 10,reservoir pressure difference within 1.50 MPa,and interval distances within 50 m are recommended to coproduce together.