Geochemical Characteristics of Shallow Groundwater in Jiaoshiba Shale Gas Production Area: Implications for Environmental Concerns

Yiman Li,Yingchun Wang,Chao Jin,Zhonghe Pang,Tianming Huang

doi:10.3390/w8120552

Abstract

The geochemical characteristics of shallow groundwater are essential for environmental impact studies in the shale gas production area. Jiaoshiba in the Sichuan basin is the first commercial-scale shale gas production area in China. This paper studied the geochemical and isotopic characteristics of the shallow groundwater of the area for future environmental concerns. Results show that the average pH of the shallow groundwater is 7.5 and the total dissolved solids (TDS) vary from 150 mg/L to 350 mg/L. The main water types are HCO3-Ca and HCO3-Ca·Mg due to the carbonates dissolution equilibrium in karst aquifers. The concentrations of major ions and typical toxic elements including Mn, Cr, Cu, Zn, Ba, and Pb are below the drinking water standard of China and are safe for use as drinking water. The high nitrate content is inferred to be caused by agricultural pollution. The shallow groundwater is recharged by local precipitation and flows in the vertical circulation zone. Evidences from low TDS, water isotopes, and high 3H and 14C indicate that the circulation rate of shallow groundwater is rapid, and the lateral groundwater has strong renewability. Once groundwater pollution from deep shale gas production occurs, it will be recovered soon by enough precipitation.

Highlights

Shale gas existing in low-permeability reservoirs has rapidly emerged as one of the vital sources of unconventional energies, and the development of multi-horizontal drilling and hydraulic fracturing technologies has paved the way for economic exploitation of shale gas resources [1,2]
Monitoring should be carried out five to six years before shale gas Baseline study is important and necessary to detect whether the groundwater is contaminated production
Pity is that shallow groundwater system baseline investigations are being are collected around shale gas production areas to be representative as geochemical characteristics performed after shale gas production in the JSB area

Summary

Introduction

Shale gas existing in low-permeability reservoirs has rapidly emerged as one of the vital sources of unconventional energies, and the development of multi-horizontal drilling and hydraulic fracturing technologies has paved the way for economic exploitation of shale gas resources [1,2]. Environmental concerns from shale gas production have drawn more and more attention from the public and regulatory bodies, in particular the composition and fate of the fluid generated by hydraulic fracturing processes in deep reservoirs [3,4,5]. Studies of typical shale gas production projects such as Marcellus and Fayetteville, both in the USA, show that contamination of groundwater system does probably exist. A relationship between methane concentrations in shallow groundwater and the proximity of drinking water wells to shale gas drilling sites in northeastern Pennsylvania is demonstrated in the Marcellus shale basin, indicating the contamination of shallow groundwater by stray gas [6]. The total dissolved solids (TDS) of flowback fluid after hydraulic fracturing always increase dramatically with time and can reach up to 300 g/L [7,8,9,10,11].

Results

Discussion

Conclusion