Characterization of Tight Sandstone Reservoirs and Prediction of Favorable Reservoirs in the Fourth Member of the Upper Triassic Xujiahe Formation in the Tianfu Area of the Sichuan Basin

doi:10.3969/j.issn.1006-6535.2024.03.003

Abstract

Abstract: The fourth member of the Upper Triassic Xujiahe Formation in the Tianfu Area of the Sichuan Basin (referred to as the T₃x₄) is characterized by thick sandstone layers interbedded with thin mudstone layers,making it a crucial exploration target for tight sandstone gas reservoirs.However,due to limitations in seismic vertical resolution,thin mudstone layers are hard to be determined by conventional methods,hindering the precise characterization of sandstone in this interval.This limitation has impeded the understanding of the distribution patterns of sand bodies in the basin and identification of favorable target areas.To address these issues, this study integrates drilling data with seismic facies and establishes a mapping relationship between the two.Under the constraint of natural gamma-ray curves,optimal inversion frequency parameters were sought to enhance the accuracy of inter-well sand body prediction.The distribution characteristics of the T₃x₄ sandstone in the Upper Triassic Xujiahe Formation were well characterized with waveform indication simulation method.The results indicate that the T₃x₄ sandstone exhibits characteristics of being thick in the west (55.0 to 100.0 m) and thin in the east (15.0 to 50.0 m).Compared to the third member of the Xujiahe Formation,the transition zone of sand body thickness variation (slope break zone) has migrated towards the interior of the craton.Analyzing data from 18 wells within the seismic working area,it was observed that beneath the slope break zone,the sandstone has a high average porosity (8.0%) and a large reservoir thickness (45.4 m).Considering tectonic evolution, sedimentary facies distribution,sandstone thickness,and porosity variations,it is proposed that the T₃x₄ follows a pattern of structures control slope break zones,and slope break zones control reservoirs.Regions below the slope break zones exhibit favorable reservoir properties with good physical characteristics and significant thickness,making them promising exploration areas.The study results provide valuable insights for the in-depth exploration of the T₃x₄.

Key words: thick Sandstone, Sandstone characterization, waveform indication simulation, well-seismic integration, reservoir prediction, Xujiahe Formation, Sichuan Basin

CLC Number:

TE121

Qiu Yuchao, Xu Qiang, Li Yibo, Deng Wei, Zheng Chao, Zhao Zhengwang, Jin Zhimin, Tan Xiucheng. Characterization of Tight Sandstone Reservoirs and Prediction of Favorable Reservoirs in the Fourth Member of the Upper Triassic Xujiahe Formation in the Tianfu Area of the Sichuan Basin[J]. Special Oil & Gas Reservoirs, 2024, 31(3): 18-26.

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