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Title: Noble isotopic gas fractionation characteristics of China's first batch commercial shale wells in the early production stage

Authors: Baojian Shen; Zhiliang He; Cheng Tao; Jincai Shen; Zongquan Hu; Zhiming Li; Wei Chen

Addresses: State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 100083, China; Wuxi Petroleum Geology Institute, Research Institute of Petroleum Exploration and Production, Sinopec, Wuxi, 214126, China ' State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 100083, China; China Petroleum and Chemical Corporation, Beijing, 100728, China ' State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 100083, China; Wuxi Petroleum Geology Institute, Research Institute of Petroleum Exploration and Production, Sinopec, Wuxi, 214126, China ' SINOPEC Chongqing Fuling Shale Gas Exploration and Development Co., Ltd., Chongqing, 408014, China ' State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 100083, China; SINOPEC Petroleum Exploration and Production Research Institute, Beijing, 100083, China ' State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 100083, China; Wuxi Petroleum Geology Institute, Research Institute of Petroleum Exploration and Production, Sinopec, Wuxi, 214126, China ' School of Energy, Soochow University, Suzhou, 215006, China

Abstract: In this study, He and Ar isotope fractionation characteristics in production gases of six Jiaoye shale wells were analysed to identify the fugitive gases occurring in overlying rocks. It was found that both radiogenic ⁴⁰Ar and ⁴He concentrations decreased first and then increased due to the release of blocked ⁴Ar and ⁴⁰He in the small pores as formation pressure dropped. However, the ⁴He/ ⁴⁰Ar ratio slightly decreased since ⁴He mitigated fast in the shale matrix. In addition, the ratio of radiogenic ⁴⁰Ar to primordial ³⁶Ar exhibited a monotonic increasing trend due to the degassing of ⁴⁰Ar from rocks. It is reasonable to assume that there was not convention through the pathway in overlying rocks created by hydraulic fracturing as the concentration difference of ³He/ ⁴He and ⁴⁰Ar/ ³⁶Ar between formation and atmosphere did not decrease. Based on noble gases information, the hydraulic fracturing did not destroy the integrity of shale formation overlying rocks. [Received: May 13, 2021; Accepted: January 27, 2022]

Keywords: shale; noble gas; isotope; diffusion; fractionation; China.

DOI: 10.1504/IJOGCT.2022.124441

International Journal of Oil, Gas and Coal Technology, 2022 Vol.30 No.4, pp.415 - 433

Received: 12 May 2021
Accepted: 27 Jan 2022
Published online: 26 Jul 2022 *