Open Access Article

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.2022.10047761

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 *