Groundwater Environment Impact Assessment Studies On Horizontal Well Development Project Of Hangjinqi Gas Field

As a clean energy,natural gas plays an important role in our life and industrial production.Currently,some hydrogeologists are gradually putting the emphasis on large-scale natural gas effect on regional groundwater environment.Once accidents such as the leakage of toxic substances in the natural gas development projects happen,it will cause serious impact on the groundwater environment.Therefore it is necessary to conduct the groundwater environmental impact assessment at the earlier stage of the gas field development zone.Using numerical simulation method to fit the flow field and forecast the trend of solute transport is an important means of quantitative environmental impact assessment of gas development and it contributes to a better grasp of evolution law the of groundwater ’s quality and quatity under the condition of natural gas exploration.The sensitive goals of the deployment zone are Boerjianghaizi lake,unconfined aquifer and confined aquifer,and the geological and hydrogeological conditions of Hangjinqi gas field are typical in the Ordos Basin region.So this paper takes the example of this gas field to study the methods and work content of groundwater environment impact evaluaion.According to the calculation,natural gas development impacts groundwater quality mainly,having smaller impact on the groundwater quantity.Considering all characteristics of the gas field and guide rules,the project belongs to class I construction project,and the grade of environment impact assessment of groundwater is second-order.Through a comprehensive analysis of groundwater quality status,the main groundwater contaminations exceeding the standard are chloride,fluoride,sulfate,nitrate,nitrite and ammonium.Overall groundwater quality of the assessment area is good.According to the lithology,hydrogeological conditions,groundwater flow field characteristics and the hydraulic connection of aquifers,the unconfined aquifer and he confined aquifer can be integrated into one whole comprehensive aquifer and the comprehensive auifer is a heterogeneous,anisotropy and spatial three-dimensional structure.The proper parameters that can make the calculated flow field match the flow field that is measured can be got through field trials repeatedly adjusting on the GMS software.The horizontal wells,methanol sewage treatment plants,frontline duty point,gas gathering station and injection wells are setted as pollutant sources and methanol,petroleum,COD and nitrite nitrogen are setted as typical contaminants.By MT3DS software numerical simulation,each leaking pollutant has a low maximum concentration and a contamination range.In addition,the center of the pollution plume has a trend of moving from the west to the east,which is the direction of dowmstream of the groundwater flow.The impact of each pollutant on groundwater environment is small,and it will not endanger Boerjianghaizi nature reserve and Shiguhao water head site.The groundwater environment can meet the relevant standards with some preventive and protective measures taken.