Self-Sourced Unconventional Tight Marlstone Reservoir Potential from Evaporative Lagoon of Triassic Leikoupo Formation in the Central Sichuan Basin

Jianyong Zhang, Yongguang Xin, Hao Zhang, Han Tian, Wei Chen and Xinjian Zhu ()
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Jianyong Zhang: PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China
Yongguang Xin: PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China
Hao Zhang: PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China
Han Tian: Research Institute of Petroleum Exploration & Development, Beijing 100083, China
Wei Chen: PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China
Xinjian Zhu: PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China

Energies, 2023, vol. 16, issue 13, 1-16

Abstract: A breakthrough was made in tight marlstone reservoirs from an evaporative lagoon in the second sub-member of the third member of the Leikoupo Formation (Lei3-2) in the Central Sichuan Basin. The source rock characteristics, reservoir characteristics of the marlstone and geochemical parameters of the oil and natural gas were investigated to evaluate the unconventional hydrocarbon exploration potential of the tight marlstone from the evaporative lagoon. The results revealed that the source rocks were deposited in evaporative lagoon environments, and the average total organic carbon (TOC) content value for the samples was 0.75 wt%. The thermal maturity of the organic matter was relatively high, with a calculated vitrinite reflectance (Rc) of 1.7%. The characteristics of marlstones suggest that the potential source rocks had fair to good hydrocarbon generative potential. The condensate samples had low densities, low viscosities and high thermal maturity, with a Rc value of 1.7%. For the natural gas, the dry coefficient was around 0.90, and the carbon isotopic compositions of methane and ethane was −41.3‰ and −28.4‰, respectively. According to the carbon isotopic compositions, thermal maturity and geological background, the oil and natural gas from Lei3-2 are comparable with the marlstone of Lei3-2. Thus, the oil and natural gas is self-sourced and originates from the marlstone in the Lei3-2. Micropores and microfractures are often detected in the marlstone from Lei3-2, and a gypsum layer is conducive to the hydrocarbon preservation. These results suggest that the evaporative lagoon facies in Lei3-2 have large, self-sourced, unconventional, tight marlstone reservoir potential. This study also enhances the prospects for further oil and gas exploration of evaporative lagoon facies in other basins.

Keywords: self-sourced unconventional hydrocarbon; tight marlstone; evaporative lagoon; Leikoupo Formation; Central Sichuan Basin (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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