Quality Evaluation Of Groundwater Environment In An Area Of Jiaoshi Shale Gas Development,Fuling City

With the increasing demand for clean energy,shale gas as a new clean energy has attracted worldwide attention.A national demonstration area of shale gas in Fuling is located between Sichuan Basin and basin edge.The terrain is mainly hilly area,and is a typical karst landform.The development of shale gas layer is located deep underground of the Wufeng-Longmaxi bottom formation mud shale.There are two important stages in the shale gas extraction process,deep drilling and fracturing gas testing.Horizontal drilling and hydraulic fracturing techniques are mainly used in the shale gas extraction process.In the developing process,potential pollution includes drilling fluids and clastic,fracturing fluids,flow-back fluid and exploitation fluid,and extraction methane gas.These potential pollution sources may pollute nearby groundwater during transportation,construction,disposal,improper treatment and other accidents.Shallow groundwater is the main drinking water source for local people.The quality of groundwater is directly related to public health.The detailed environmental research of groundwater near shale gas wells has already started abroad,while the domestic research just begins.The water environmental quality assessment research in Jiaoshi area is almost blank.This research evaluated the quality of groundwater environment via single gene index method,complex indices method and so on.The analysis is based on the survey data of groundwater in the area of Jiaoshi shale gas development,Fuling City.The main research contents include: the quality evaluation of groundwater,the calculation of background value,and the pollution evaluation of groundwater,and other aspects of groundwater environment.The resulted show that the groundwater quality of the study area was generally good,and up to 96.23% of our samples reached standard.The inorganic toxicological indexes,including barium,cadmium and chromium concentration values,reach Grade II drinking water standard.Two underground karst water spots are polluted by shale gas drilling fluids and oil leakage from equipment,and the mud for plugging during the shale gas production.So they are not recommended to be local drinking water supplying spots.Other groundwater points can basically meet the different local demands.The research showed that the factors related to shale gas exploration and development are: sodium,chlorine,manganese and barium,in whichsodium and chlorine are the strongest correlation,and manganese,barium followed.Sulfate is hardly irrelevant to shale gas development.Copper,pH,zinc,iron,cadmium,and hexavalent chromium are not related to shale gas development.Finally,the groundwater environment in the area of shale gas development was characterized,including groundwater quality characteristics,pollution status,and other aspects.This study provides basis data and technical support for local security of groundwater,establishes the groundwater standards of shale gas development in karst area,and promote development of shale gas.