Water-Energy Nexus Simulation And Multi-level Decision Making For Alternative Energy

Recently,unconventional energy sources,such as shale gas,are conaidered as the most potential alternative energy source,which have attracted wide attention of governments all over the world.Exploration and exploitation of shale gas is of great strategic significance to reduce the increasing contradiction between supply and demand of conventional oil and gas and to ensure national energy security.However,the traditional optimization models are difficult to solve the complex-enhanced decision-making problem due to multiple uncertainites in the multi-objective and multi-level optimization processes.The shale gas supply chain is complicated with uncertainties associated with environmental,economic and technical parameters,such as the estimated ultimate recovery(EUR),fracturing water consumption,greenhouse gas emission intensity and wastewater treatment facility capacity.Such uncertainties could not only affect the related shale gas transportation and distribution process,but also affect the final optimal energy management shemes.It is thus increasingly urgent to strengthen the scientificity of the overall decision-making process of shale gas supply chain under multiform uncertainties for meeting the multiple needs.Based on simulation of gas-water two-phase flow in shale gas reservoirs and analysis of carbon-water footprint,this thesis develops a series of uncertain-based optimization models according to non-cooperative game theory,which can provide reference for shale gas sustainable developmemt.The major contents of this thesis are summarized as follows:(1)based on the typical production characteristics of shale gas,the gas-water two-phase seepage models of matrix and fracture subsystems are established,and the migration behaviors of shale gas and water flow in reservoirs are presented through numerical simulation.Combined with factor analysis,the influences of various matrix,fracture and fluid properties on system productivity are quantitatively analyzed.Results show that the facture spacing has major and negative effects on cumulative gas production,while fracture permeability and gas diffusion coefficient have obvious interaction on system productivity.The simulation technology can not only identify the impacts of different factors on system productivity,but also provide data support for subsequent optimization model development.Combined with the life cycle assessment and Tsinghua-CA3EM model,the energy-carbon-water footprints of shale gas are quantitatively evaluated,which are also use to compare with the corresponding solutions regarding conventional energy sources(i.e.,natural gas and coal).An optimization model with respect to carbon-water regulation is then proposed.Results indicate that the optimal fugitive methane emission rate would be[5.75%,7.89%]and the optimal recycling rate of flowback and produced waters would reach[0.37,0.80]with considering multiple technical constraints.(2)With respect to the hierarchical relationship between different decision objectives,a bi-level programming method based on non-cooperative game is introduced in this study,where the interval programming is used to reflect the uncertain information,and the fractional programming is used to reflect the economic and environmental efficiencies of the system.The interval bi-level fractional programming model is then applied into the Marcellus shale supply chain in Pennsylvania,Results reveal that the cumulative shale gas production obtained from the bi-lelvel model would decrease by[38.44%,85.84%]as compared with that generated from the economically-aggressive model,but it would significantly increase by[38.88%,85.93%]when compared with that under the environmentally-aggressive model.In terms of the economic performance,it would reduce by 11.84%and increase 15.39%when respectively compared with the economically-and environmentally-aggressive models.Comparing with the results of single-objective programming and multi-objective programming,results display that the sustainable development of regional unconventional energy sources would be realized especially through synthesizing and balancing the resource allocation schemes of different levels of decision making.(3)The upstream,middle and downstream of shale gas supply chains involve different stakeholders,and stochastic information in the EUR normally has a significant impact on the economic and environmental performances of the shale gas supply chains.Consequently,this study advances a dominant-subordinate chance-constrained programming(DSCCP)model for optimizing shale gas supply chain,which can forecast shale gas production,allocate water resources,and identify the environmental implication of flowback and produced(FP)waters under uncertainty.Multiple techniques involving game theory,structural optimization,process design,cost analysis,environmental assessment,and stochastic simulation are merged into a general modeling framework.Then,the developed model is used for a practical shale supply chain in Beaver Country.A fuzzy satisfaction degree algorithm under interference of stochastic factors is proposed to obtain comprehensive strategies in line with the upstream and downstream decision makers.Results disclose that the variation in violation levels would result in different environmental and economic performances.A higher probability level of the EUR value woud correspond to a lower EUR value,resulting in lower economic benefits and freshwater supply;in comparison,a lower probability level of EUR value would lead to higher economic benefits and freshwater supply,and the system reliability would also increase.Therefore,decision makers need to weigh the dynamic relationship between objective function value and system risk in order to make the optimal decisions.In addition,the MPS model with more emphasis on the upstream economic objective would provide an economic-oriented management strategy,which could meet the needs of upstream shale gas developers to a certain extent,but seriously violate the needs of downstream power generation sector;the MCS and MWS models respectively with downstream system cost minimization and upstream water use minimization concerns would tend to formulate conservative management strategies;the major difference between the two models lies in the MWS model with more attention to wastewater recycling.When hierarchical decision-making is not considered,the optimization results of MPWS model(both consideration of upstream system benefit and water use)can be used as an alternative to the results of DSCCP model.(4)The shale gas supply chain usually involves complex issues,such as greenhouse gas emissions,economic benefits and wastewater management,and the corresponding decision makers are raised from different management levels with internal relations between superiors and subordinates.Accordingly,this study develops a shale-gas-water multi-level programming model,which integrates greenliouse gas emission control,shale gas economic production and water resources efficient utilization modules into the whole life cycle supply chain.The multi-level programming can elevate incapacity of conventional bi-level programming in addressing an enhanced complex leader-follower relationship between different decision makers.The effectiveness and capabilities of the multi-level model are illustrated through real-world case studies of the Barnett,Marcellus,Fayetteville,and Haynesville Shales.An improved multi-level interactive solution algorithm based on satisfactory degree is proposed for improvng computational efficiency.Results show that traditional bi-level programming models still develop environmental or economic preference policies,while multi-objective programming and multi-level programming models can help to formulate more comprehensive economic and environmental decision-making schemes because they consider more dimensions of objective functions.However,the traditional multi-objective programming model fails to fully consider the hierarchical structure of decision-makers in shale gas supply system7leading to slightly subjective strategies difficult to be adopted by decision-makers.These findings can not only help to evaluate the economic and environmental impacts of shale gas supply system,such as potential greenhouse gas emissions,water-energy consumption,wastewater treatment,but also effectively avoid conflicts of interest among different decision makers,thus obtaining a non-compromise optimal management scheme.