Evaluation Of Water Environment Carrying Capacity And System Dynamics Model For Shale Gas Development In Weiyuan County

With the rapid development of society and economy,the demand for conventional fossil energy in China is constantly increasing and the contradiction between supply and demand is increasingly intensified.In order to relieve the energy pressure,reduce the dependence on foreign energy and improve the energy structure,it has become an important choice to accelerate the development and utilization of unconventional oil fields such as shale gas.However,shale gas development is an environmental impact project.During the whole development process,a large amount of water resources is consumed,and a variety of harmful chemical additives in fracturing fluids pollute water bodies,which brings many environmental problems.In recent years,China has actively explored shale gas and carried out exploration and evaluation of shale gas resources,mainly focusing on the research and development of stimulation and efficiency enhancing technologies to promote shale gas development.There are few studies on the environmental impact caused by shale gas development.In view of this,it is necessary to carry out evaluation and analysis of water environment carrying capacity in shale gas development areas.Firstly,through literature investigation and research,combined with the general situation of shale gas development process and research area,and based on the existing national laws and regulations related to water environment and the indicators in relevant literature,a fuzzy comprehensive evaluation model was built.Through correlation analysis,19 common indicators and 4 individual indicators were selected,and the comprehensive weight was obtained by combining subjective and objective weights,which constructed the evaluation index system of water environment carrying capacity for shale gas development with social economy,water resources and water environment as subsystems.The results show that the scoring value of water environment carrying capacity of shale gas development in Wei yuan County is within the range of 0.247 ～0.764 during 2009 to 2018,showing an overall upward trend from critical bearing state to suitable bearing state.The scoring value of water resource subsystem was in a downward trend,and the average scoring value reached 0.622 during the research period,which was relatively high.The scoring value of social economic subsystem and water environment subsystem showed an upward trend,which laid a foundation for the improvement of water environment carrying capacity.High population density,high utilization rate of water resources development,high annual total water consumption,low per capita water resources,and low flow back rate of fracturing fluid is the main constraint factor.Secondly,combined with the economic conditions,natural environment and shale gas development status of Weiyuan County,the restricting factors of the water environment carrying capacity of shale gas development are analyzed from the overall perspective,and the modeling is carried out based on the system dynamics modeling concept.By setting up four simulation schemes,the overall trend of water environment carrying capacity of shale gas development in Wei yuan County from 2019 to 2028 was predicted and simulated through rationality test and sensitivity analysis from four perspectives of social economy,water environment,water resources and shale gas.The results show that the water environmental carrying capacity of shale gas development in the current development plan is on the rise,but the rate of increase is slow.The initial value of the environmental development scheme is not high,but the rate of improvement is fast in the short term,which indicates that the development mode of this scheme can significantly improve the water environmental carrying capacity in the short term.In the economic development plan,the water environment carrying capacity of shale gas development shows a decreasing trend in 2021,indicating that priority economic development will directly damage the water environment and is not conducive to sustainable development.In the coordinated development plan,the water environment carrying capacity of shale gas development increased at the fastest rate.Therefore,the coordinated development program is an ideal program to realize the sustainable development of regional economy and shale gas exploitation.In this thesis,the analytic hierarchy process(AHP),fuzzy comprehensive evaluation method and system dynamics method are combined.From the current situation analysis to simulation prediction,the water environmental carrying capacity of shale gas development in Weiyuan County is studied as a whole,from the whole to subsystems,and finally to the comprehensive analysis and evaluation of each factor index.In order to provide scientific basis and reasonable suggestions for improving water environmental carrying capacity of shale gas development in Weiyuan County.