The sedimentological reservoir characteristics of the Jurassic Sangonghe Formation, Southern Mahu Slope, Junggar Basin, Northwestern China

Abstract

The hydrocarbon discoveries are increasing in deltaic systems in Jurassic Sangonghe Formation in southern Mahu Slope of Junggar Basin in recent years. However, different scales of sedimentological heterogeneities influence reservoir quality and architecture. Consequently, the study aims to employ thin sections, core logs and wireline logs to conduct research to address the issues. The results show that the integrated analysis of conventional cores reveals three facies groups in Sangonghe Formation which are deposited in braided deltaic and lacustrine environment. Each facies group contains several lithofacies given their grain size, sedimentary structures. In addition, the lithofacies types, associations, and wireline responses indicates that Lower, Middle, and Upper Sangonghe Formation is deposited in braided delta plain, braided delta front, and pro‐delta respectively. Moreover, the Sangonghe Formation is characterized by variations regarding sandbody, thickness, geometry, and architecture. The facies distribution and sedimentary environment indicate that accommodation space plays essential controls. The sedimentological heterogeneity controls reservoir quality and architecture from macro‐ to micro‐scale. The macro‐scale insights reflect that the lower and middle Sangonghe Formation shows high connectivity of sandbodies while the upper Sangonghe Formation shows low connectivity of sandbodies. The micro‐scale insights indicate that sandstone types, texture, composition all plays significantly role in controlling reservoir porosity and permeability. Finally, the understandings and insights of reservoir sedimentological heterogeneities assist in better prediction and assessment of reservoir quality and architecture. Finally, it will make contributions to reservoir development, recovery, and productivity for areas with similar sedimentological settings.

The controlling effect of sedimentary characteristics on the heterogeneity of the Chang 6 reservoir in the Wuliwan area

“…Gamma ray logs are analyzed for the purpose of detecting a clean interval (indication of more sandy) and a dirty interval (indication of more muddy). Given the fact that the GR value is high at muddy units and low at sandy units (Qiu et al, 2020), we can make appropriate interpretations. It is often difficult to identify the bedding type of lithofacies by using cable logging.…”

Sedimentary Microfacies and Sand Body Characteristics at Segment 2 of the Sangonghe Formation in Oilfield A on the South Slope District of the Mahu Depression

“…The steepness of the paleotopographic slope determines the strength of hydrodynamics during deposition: the greater the slope, the stronger the hydrodynamics, the smaller the area of delta it controls; conversely, the smaller the slope, the weaker the hydrodynamics, the larger the area of delta it controls. The slope of the study area is relatively small during the sedimentation stage, and it is the sedimentation background of a gentle slope [30]. A comparative analysis of strata was carried out on more than 80 wells in the study area by combining logging data and seismic model inversion.…”

“…Moreover, the burial depth is low, and the reservoir strata have good properties. This field is important for lithology, oil, and gas reservoir exploration [19,20]. Sand Group 4 at Segment 2 of the Sangonghe Formation is a main oil-producing segment in the study area where the sand body is 5-20 m thick.…”

Pore Structure and Movable Fluid Characteristics of Typical Sedimentary Lithofacies in a Tight Conglomerate Reservoir, Mahu Depression, Northwest China

“…A large set of fan delta plain subfacies conglomerate and conglomerates bodies are deposited on the edge of the basin, and fan delta front subfacies conglomerates, conglomerate sandstone, and sandstone are deposited toward the center of the lake basin. The total thickness of the reservoir exceeds 1500 m. , Therefore, the research layer lithology is dominated by gray, gray-green, and brown conglomerates and pebbly sandstone (Figure C), with typical conglomerates sedimentary microfacies such as debris flow/clastic flow, braided channel, underwater distributary channel, fan channel, etc. Conglomerates modalities are significantly different, and sedimentation and diagenesis have an important impact on reservoir development. , …”