【作者】 温震洋；

【导师】 王志荣；

【作者基本信息】 郑州大学 ， 水利工程（专业学位）， 2022， 硕士

【摘要】 中国北方尤其是黄河流域煤岩储层的地下水害尤为严重,上石炭与中奥陶统岩溶水发育,水量大,水头高,且各含水层水力联系较为密切,水力压裂技术条件下的地下水环境保护面临巨大挑战,构建高精度的煤层气垂直井涌水量预测模型具有非常重要的现实意义。以往的水力压裂模型都将煤岩简化为致密岩体进行研究,忽略了煤岩储层中原生裂隙对水力压裂行为的影响,且现有研究未全面考虑在压裂抽采条件下储层力学渗透特性变化对涌水量的影响。基于此,本文以河南省焦作矿区为例,在充分收集研究区水文地质条件和涌水量实测数据的基础上,基于弹性力学、断裂力学、地下水动力学和水文地质学等理论,深入分析水力压裂过程,考虑储层原生裂隙几何特征和压裂抽采过程中储层力学渗透特性变化规律,进行了关于煤层气垂直井涌水量预测的一系列研究。运用应力场理论分析垂直井井筒周围煤岩的应力状态,考虑射孔应力的二次应力改造和压裂液渗透作用产生的渗透体积力,基于断裂力学裂纹强度准则,引入原生裂隙几何特征参数,建立了裂隙性煤岩储层的起裂压力模型;结合裂隙性煤岩储层中水力裂缝扩展延伸过程中应力损伤对煤岩本体变形的影响,构建了煤岩体损伤本构关系,在起裂压力模型的基础上,推导得到了裂隙性煤岩储层中水力裂缝延伸压力的计算公式。基于经典的PKN水力裂缝扩展模型,根据水力裂缝内压裂液体积守恒规律,建立了改进的裂隙性煤岩储层水力裂缝扩展模型,得到了水力裂缝长度L随压裂时间变化的关系;考虑抽采过程中水力裂缝内净压力的非线性压降规律,结合抽采过程煤岩储层压力梯度的变化对煤岩储层原生裂隙和水力裂缝几何尺寸的影响,得出了水力裂缝宽度w随着抽采时间的变化关系。根据裂缝内部定黏滞系数和密度的N-S方程,结合水力裂缝宽度动态变化规律,推导出了煤岩储层动态渗透系数表达式;基于地下水动力学原理和井流理论,建立一定边界条件和初始条件下煤岩储层地下水运动的定解问题方程,利用定解问题的解析,继而建立了煤层气垂直井涌水量预测模型;运用该模型对研究区内四口煤层气垂直井进行了试验期涌水量计算,并与实际生产资料对比,平均涌水量相差1.95%～5.96%,二者基本吻合,验证了煤层气垂直井涌水量预测模型的正确性;进而对四口煤层气垂直井生产期内的涌水量进行长期预测,并分析了影响煤层气垂直井涌水量的因素。更多还原

【Abstract】 Reservoir of coal and rock in northern China,especially the Yellow River basin is particularly serious,underground water disasters in the carboniferous and the ordovician karst water development,water,high water head,and each aquifer hydraulic contact closely,hydraulic fracturing technology under the condition of groundwater environment protection faces huge challenges,the construction of a high precision of coalbed methane well water inflow forecast model has very important practical significance.In the past hydraulic fracturing models,coal rock was simplified as dense rock mass,and the influence of primary fractures in coal rock reservoir on hydraulic fracturing behavior was ignored,and the influence of changes in mechanical permeability characteristics of reservoir on water inflow under fracturing and extraction conditions was not fully considered in the existing studies.Based on this,this article in jiaozuo mining area of henan province as an example,in the full collection of hydrogeological conditions and water inflow in the study area,on the basis of the measured data,based on elastic mechanics,fracture mechanics,hydrogeology and groundwater dynamics theory,in-depth analysis of the hydraulic fracturing process,considering the primary fracture geometry characteristic and reservoir fracturing permeability reservoir under the condition of extraction from mechanics properties change rule,A series of researches on the prediction of water inflow in coalbed methane vertical Wells are carried out.The stress field theory was used to analyze the stress state of coal rock around the vertical wellbore.Considering the secondary stress reconstruction of perforating stress and the permeable volume force generated by fracturing fluid permeability,the fracture initiation pressure model of fractured coal rock reservoir was established by introducing the geometric characteristic parameters of primary fractures based on the fracture mechanics crack strength criterion.Combined with the influence of stress damage on the deformation of coal and rock body in the process of hydraulic fracture extension in fractured reservoir,the damage constitutive relation of coal and rock body is established.Based on the fracture initiation pressure model,the calculation formula of hydraulic fracture extension pressure in fractured reservoir is established.Based on the classical PKN hydraulic fracture propagation model,an improved hydraulic fracture propagation model for fractured reservoirs was established based on the conservation law of fracturing fluid volume in fractures,and the relationship between hydraulic fracture length L and fracturing time was obtained.Considering the nonlinear pressure drop law of net pressure in hydraulic fracture in the process of pumping and combining with the influence of the change of pressure gradient of coal and rock reservoir on the geometric size of primary fracture and hydraulic fracture in coal and rock reservoir during the process of pumping and mining,the relationship between the width of hydraulic fracture W and the time of pumping and mining is obtained.According to the n-S equation of fixed viscosity coefficient and density inside the fracture,and combined with the dynamic variation law of hydraulic fracture width,the dynamic permeability coefficient expression of coal and rock reservoir is deduced.Under certain boundary conditions and initial conditions,based on the theory of groundwater dynamics and well flow theory,the equation of fixed solution problem of groundwater movement in coal rock reservoir is established,and then the prediction model of water inflow of coalbed methane vertical well is established by the analysis of fixed solution problem.The model is used to calculate the water inflow of four coalbed methane vertical Wells in the study area during the test period,and compared with the actual production data,the average water inflow difference is about 1.95%～5.96%,and the two are basically consistent,which verifies the correctness of the prediction model of water inflow of coalbed methane Wells.Then the water inflow of four CBM experimental Wells in the production period is predicted and the factors affecting the water inflow of CBM Wells are analyzed.更多还原