Optimization Of Water Pollution Management For Shale Gas Development Based On Decision Analysis

Under the circumstance that conventional energy has not been able to meet China's increasing energy demand,developing shale gas is one of China's resource strategies to deal with the energy crisis in the future,and it is highly valued by the parties.However,with the increasing maturity of shale gas drilling technology,the formation and surface water pollution that may be caused by large-scale "hydraulic fracturing" has become a major issue for shale gas development.This thesis focuses on the problem of water pollution in the development of shale gas.A fracturing fluid treatment cost optimization model is established in this thesis based on the fracturing and flowback fluid treatment and dispatch in the shale gas field,quantitatively analyzing the cost structure,and considering the constraints of production period and the inter-block location.Mainly completed works are as follows:1)A shale gas water pollution indicator system is established according to domestic industrial pollutants discharge standards,and based on the existing industrial pollution emission standards,shale gas development waste management and other related legal norms.According to the concentration of the pollution index,the pollution degree of the fracturing and flowback fluid of the shale gas reservoir is quantified and graded which is divided into general pollution,strong pollution and very strong pollution.2)The gray cluster method is used to improve the evaluation method of cloud model.The grey entropy method,the analytic hierarchy process and the expert scoring method are employed to improve the weight scoring method of cloud indicators at all degree.Based on the water pollution index grading system established in the previous section,the pollution degree of shale gas fracturing and flowback fluid in different areas is evaluated using a comprehensive cloud model method to rank the levels of pollution.The comprehensive evaluation method based on the improved cloud model takes into account the randomness and ambiguity of the data,which effectively reduces the impact of these uncertainties,and can evaluate the different types of flowback fluid pollution degrees quantitatively.3)Through quantitative analysis,a treatment-disposal cost optimization model in block,the treatment-disposal-transportation cost optimization model inter-block are established.The optimization of treatment and disposal costs for full-cycle at various stages of production is considered.Based on the model of return-discharge fluid disposal and transportation optimization between blocks,this model comprehensively considers the fracturing fluid requirements and processing capacity constraints of different blocks in different fracturing-backflow stages.The model is solved under different parameters,and a full-cycle treatment-disposal-transport cost optimization scheduling scheme for shale gas field fracturing and flowback fluid is obtained.4)The expected utility model of decision analysis is applied to analyze the resulting dispatching plan and calculate the degree of agreement Hi of different plans so as to select the best plan and achieve the economical and low-pollution purpose.Above all,the possible pollution degree of shale gas in developing hydraulic fracturing in this thesis is analyzed.And an appropriate treatment-disposal cost optimization model is established,which can be used for providing effective quantitative analysis and theoretical support on fracturing and flowback fluid management and scheduling in shale gas field.