Prediction of total organic carbon of high-quality source rocks and their control on hydrocarbon accumulation in strongly heterogeneous rift lake basin: a case study of Gegangji area, Dongpu Sag

doi:10.3969/j.issn.1672-7703.2025.06.014

Abstract

Abstract: In Gegangji area, Dongpu Sag, the distribution of high-quality source rocks in Shahejie Formation exhibits extremely strong heterogeneity, making it difficult for conventional logging methods to accurately identify and predict, which significantly hinders effective oil and gas exploration in the subsag area. By integrating geochemical data with logging response characteristics, and employing a random forest algorithm, a high-precision TOC prediction model has been developed, achieving effective prediction of total organic carbon (TOC) content of source rocks in the context of highly heterogeneous geological conditions, which reveals the distribution pattern of high-quality thin source rocks and their controlling effect on hydrocarbon accumulation. The study results indicate that the high-quality source rocks in the study area are mainly composed of gray black shale, with high organic matter abundance, and favorable kerogen types, but thin single-layer thickness, rapid vertical and lateral variations, and complex logging response, leading to insufficient identification accuracy of traditional methods. The random forest algorithm significantly improves the prediction capability for heterogeneous organic matter distribution in complex lithological associations by integrating multi-type logging parameters. The prediction results show that high-quality source rocks are mainly distributed at the base lower sub-member of the third member (Es₃^l) and the middle-upper part of the upper sub-member of the fourth member of Shahejie Formation (Es₄^u) in the study area. Moreover, their thickness gradually increases from west to east and from south to north in the near-subsag to deep-subsag areas. The distribution of high-quality source rocks had a clear control on hydrocarbon accumulation, demonstrating typical characteristics of “near-source rock hydrocarbon accumulation”. The high-yield oil and gas layers as well as hydrocarbon-bearing intervals are all located near high-quality source rocks, and the degree of hydrocarbon enrichment is closely related to source rock thickness. This research provides an important geological basis for oil and gas exploration planning in the subsag area in Dongpu Sag.

Key words: high-quality source rock, heterogeneity, random forest, controlling effect on hydrocarbon accumulation, Shahejie Formation, Dongpu Sag

CLC Number:

TE122

Gao Yongtao, Li Lu, Guo Dong, Song Xiaohang, Pan Yongshuai, Xu Tianwu. Prediction of total organic carbon of high-quality source rocks and their control on hydrocarbon accumulation in strongly heterogeneous rift lake basin: a case study of Gegangji area, Dongpu Sag[J]. China Petroleum Exploration, 2025, 30(6): 201-214.

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