Groundwater Baseline Water Quality in a Shale Gas Exploration Site and Fracturing Fluid - Shale Rock Interaction

Abstract

Hydraulic fracturing for shale gas exploration is not free from environmental risk. The environmental concerns related to hydraulic fracturing has been greatly attracted. One of most important environmental concerns is regional water quality which may be contaminated by produced waters through induced and natural fractures and wastewater discharge. At present, the baseline water quality must be firstly obtained to identify potential pollution of the activity and monitoring indicators should be studied for better environmental monitoring. We sampled shallow groundwater, produced waters, shale rock and soil in the Jiaoshiba shale-gas region, SW China and measurements have included water chemistry and isotopes. Preliminary results show that the present shallow karst groundwater quality is pretty good with the total dissolved solids (TDS) ranging from 129 to 343mg/L and with water chemistry type of HCO3-Ca, However, some groundwaters have been polluted by agricultural activities. Produced waters have relatively high salinity with TDS ranging from 2 to 14g/L. Laboratory experiment of fracturing liquid and shale rock interaction at simulated reservoir conditions shows that TDS in the flowback fluid increases 10 times and Ca2+, Na+, Cl− and SO42− make dominant contributions. The main geochemical reactions are inferred to be pyrite oxidation and the dissolution of calcite, dolomite and plagioclase, resulting in increases of major ions in the flowback fluid. The inorganic geochemical monitoring indicators for shale gas exploration of the Silurian Longmaxi formation has been determined.