Hydrogeochemical and isotopic evidences of the underlying produced water intrusion into shallow groundwater in an oil production area, Northwest China

Hongyu Zhang; Xu Han; Guangcai Wang; Ling Zhou; Dandan Huang; Xianglong Chen; Fan Zhang

doi:10.1016/j.scitotenv.2024.170242

Hydrogeochemical and isotopic evidences of the underlying produced water intrusion into shallow groundwater in an oil production area, Northwest China

Sci Total Environ. 2024 Mar 15:916:170242. doi: 10.1016/j.scitotenv.2024.170242. Epub 2024 Jan 24.

Authors

Hongyu Zhang¹, Xu Han², Guangcai Wang³, Ling Zhou⁴, Dandan Huang⁵, Xianglong Chen¹, Fan Zhang¹

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology & MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences, Beijing 100083, China; School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China.
² Geology Institute of China Chemical Geology and Mine Bureau, Beijing 100028, China.
³ State Key Laboratory of Biogeology and Environmental Geology & MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences, Beijing 100083, China; School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China. Electronic address: wanggc@pku.edu.cn.
⁴ Beijing Key Laboratory of Urban Hydrological Cycle and Sponge City Technology, College of Water Sciences, Beijing Normal University, Beijing 100875, China.
⁵ School of Water Resources & Environment Engineering, East China University of Technology, Nanchang, Jiangxi 330013, China.

PMID: 38278275
DOI: 10.1016/j.scitotenv.2024.170242

Abstract

The extensive use of fossil fuels (e.g., oil) poses a hidden danger to groundwater quality. However, inorganic pollution has received limited attention compared to organic pollution. In this study, the potential contaminant sources to shallow groundwater were investigated using hydrochemical (e.g., major and trace elements) and isotopic (δ²H and δ¹⁸O) methods at an oil field, northwest China, with emphasis on the identification of produced water (PW; oil production-related water) intrusion. The results showed that the groundwater samples can be chemically and isotopically classified into two groups: Group A (severely polluted) and B (slightly or non- polluted). The hydrochemical characteristics of Group A were similar to that of PW, with a comparable Na⁺/Cl^- ratio and elevated levels of Na⁺, Ca²⁺, Cl^-, Br^-, Sr, Ba, Li, B and total volatile organic compounds (TVOCs; volatile and semi-volatile) concentration, but lower HCO₃^- and SO₄^2- contents, and depleted δ²H and δ¹⁸O, which was not suitable for drinking. Groundwater salinity sources involve mineral dissolution (silicate, carbonate and evaporite), cation exchange and anaerobic microbial degradation, as well as deep PW intrusion (especially in Group A). The Cl mixing model showed that PW contributed 13.63-27.78 % to Group A, supported by the results of the isotope mixing model based on δ²H and δ¹⁸O (24.43-33.29 %). An overall pollution conceptual model involves three modes: fracturing, surface infiltration, and groundwater lateral runoff. This study validates the effectiveness of Na, Cl, Br, Sr, Ba, Li and B as favorable tracers for monitoring PW intrusion.

Keywords: Hydrochemistry; Indicators; Pollution modes; Produced water; Water stable isotopes.