Ion and Stable Isotope Geochemistry of Produced Water in Coalbed Methane Wells in the Tiefa Basin

Huazhou Huang; Chuanxia Tong; Zhengqing Wu; Junjie Ding; Zaixing Huang; Huan He; Jinbo Zhang

doi:10.1021/acsomega.3c06340

Ion and Stable Isotope Geochemistry of Produced Water in Coalbed Methane Wells in the Tiefa Basin

ACS Omega. 2023 Oct 13;8(42):39896-39906. doi: 10.1021/acsomega.3c06340. eCollection 2023 Oct 24.

Authors

Huazhou Huang^{1

2

3}, Chuanxia Tong⁴, Zhengqing Wu⁴, Junjie Ding⁵, Zaixing Huang⁶, Huan He⁶, Jinbo Zhang^{2

3}

Affiliations

¹ Jiangsu Key Laboratory of Coal-Based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou 221008, China.
² Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, China University of Mining and Technology, Ministry of Education, Xuzhou 221008, China.
³ School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China.
⁴ The Third Exploration Team of Anhui Coalfield Geology Bureau, Suzhou 234000, China.
⁵ Yellow River Engineering Consulting Co., Ltd., Zhengzhou 450003, China.
⁶ School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, China.

Abstract

The potential geochemical information in the produced water of coalbed methane (CBM) wells is conducive to the exploration and development of CBM in the case that the produced water is primitive formation water. A total of 58 produced water samples collected from 13 CBM wells in the Daxing Mine, Tiefa Basin, were investigated. Ionic composition tests and stable isotope analysis were conducted to explore the geochemical characteristics and sources of produced water as well as the method for determining whether the produced water is primitive formation water. The results suggest that the fracking fluid for CBM stimulations is the main factor affecting the ion change of the produced water in the initial stage of drainage. The concentrations of Cl^- and Ca²⁺ + Mg²⁺ could be taken as the indices to identify whether the produced water is primitive formation water. When the Cl^- concentration is lower than 20 mEq/L and the Ca²⁺ + Mg²⁺ concentration is lower than 1 mEq/L, the produced water is close to the pristine formation water. Biogenic methanogenic activity may result in a high δ¹³C_DIC and high concentrations of HCO₃^- in the pristine formation water in the Tiefa Basin. The data of δD and δ¹⁸O in the study area suggest that the formation water might come from atmospheric precipitation, which is later affected by evaporation and the water-rock reaction. The hydrogen isotope values in the produced water derived from the lower coal group display a substantial elevation compared to those from the upper coal group. This disparity in the hydrogen isotope composition presents an opportunity to utilize δD in produced water as a tool for distinguishing the formation water between these two groups.