Occurrence states and mobility of shale oil in different lithologic assemblages in the Jurassic Lianggaoshan Formation, Sichuan Basin

Rui FANG; Yuqiang JIANG; Changcheng YANG; Haibo DENG; Chan JIANG; Haitao HONG; Song TANG; Yifan GU; Xun ZHU; Shasha SUN; Guangyin CAI

doi:10.11743/ogg20240313

| Sign up

Cite

EndNote(RIS) BibTeX

Collect

Submit Manuscript

Show Outline

Outline

Abstract

Keywords

References

Show full outline

Hide outline

Publishing Language: Chinese

Occurrence states and mobility of shale oil in different lithologic assemblages in the Jurassic Lianggaoshan Formation, Sichuan Basin

Rui FANG^{¹^,²}, Yuqiang JIANG^{¹^,²}, Changcheng YANG^³, Haibo DENG^⁴, Chan JIANG^⁵, Haitao HONG^⁶, Song TANG^⁷, Yifan GU^{¹^,²}(), Xun ZHU^³, Shasha SUN^⁸, Guangyin CAI^¹

School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China

Reservoir Evaluation Sub-Laboratory, Key Laboratory of Unconventional Oil and Gas, CNPC, Chengdu, Sichuan 610500, China

Gas Field Development Management Department, Southwest Oil & Gasfield Company, PetroChina, Chengdu, Sichuan 610056, China

Tight Oil and Gas Exploration and Development Project Department, Southwest Oil & Gasfield Company, PetroChina, Chengdu, Sichuan 610051, China

Exploration Division, Southwest Oil & Gasfield Company, PetroChina, Chengdu, Sichuan 610051, China

Exploration and Development Research Institute, Southwest Oil & Gasfield Company, PetroChina, Chengdu, Sichuan 610041, China

Central Sichuan Oil & Gas Field, Southwest Oil & Gasfield Company, PetroChina, Suining, Sichuan 629000, China

Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China

Show Author Information

Abstract

Based on a systematic analysis of the data from well cores, we divide the lithologic assemblages of shales in the Jurassic Lianggaoshan Formation in the Sichuan Basin into pure, shelly, and silty categories, which are further categorized into five types. A summary of differences in the macroscopic and microscopic characteristics of shale reservoirs of different lithologic assemblages is then deduced to identify and evaluate the occurrence states and mobility of fluids in these reservoirs, and determine the optimal lithologic assemblage types. The results indicate that the shale oil in the Lianggaoshan Formation is of free and adsorbed types, with the former occurring as movable and/or irreducible oil. Among shale pores, small pores primarily contain adsorbed and irreducible oil, mesopores largely hold irreducible and movable oil, and macropores mainly contain movable oil. The 2D nuclear magnetic resonance (NMR) analysis reveals that zones with T₂ ≥ 0.2 ms and 1 ≤ T₁/T₂ < 10 represent the signals of movable and irreducible oil and those with T₂ < 0.2 ms and 10 ≤ T₁/T₂ < 100 denote the signals of adsorbed oil. This enables the establishment of an identification chart of 2D NMR T₁-T₂ spectra for fluids of different occurrence states in the Lianggaoshan Formation. The pore size conversion based on the NMR analysis reveals that pores containing free oil in shales of the formation have a minimum pore size of 60 nm. Accordingly, a classification scheme for pores in the shale oil reservoirs is developed based on pore size and the occurrence state of fluids. Factors directly affecting the occurrence and mobility of shale oil in the Lianggaoshan Formation are identified as organic matter content, fluid flowability, mineral composition, and pore structure. The silty shale assemblage, characterized by well-developed macropores and microfractures and a high proportion of pores containing movable oil, is favorable for the enrichment of movable oil. Besides, its silty laminae provide both substantial reservoir spaces and enhance pore connectivity, which create favorable conditions for the accumulation, occurrence, and flow of shale oil. Therefore, the silty shale assemblage stands as a favorable lithologic assemblage category in the Lianggaoshan Formation, with intervals where this assemblage occurs serving as play fairways for shale oil exploration and exploitation in the Lianggaoshan Formation, Sichuan Basin. Therefore, determining the pore-fracture configuration in the silty shale assemblage is of primary significance in research to achieving breakthroughs in shale oil exploration and exploitation of the Lianggaoshan Formation.

Keywords

mobility occurrence state 2D NMR T₁-T₂ spectrum lithologic assemblage shale oil Lianggaoshan Formation Sichuan Basin

CLC number: TE122.2 Document code: A Article ID: 0253-9985(2024)03-0752-18

References

[1]

Administration U S E I. Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States[J].2013.

[2]

ZHOU Qingfan, JIN Zhijun, YANG Guofeng, et al. Shale oil exploration and production in the U.S.: Status and outlook[J]. Oil & Gas Geology, 2019, 40(3): 469-477.