青海共和盆地干热岩热储层人工水力致裂裂缝扩展规律

Artificial hydraulic fracture propagation law of hot dry rock reservoir in Gonghe Basin,Qinghai province

干热岩热储层裂隙的渗透性、连通性直接影响着其换热效果,水力压裂是增强裂隙特性的重要手段。为了掌握水力压裂时裂缝的扩展规律,以青海共和盆地GR1地热井3500~3705 m深度段为研究对象,通过对ABAQUS水力压裂模拟软件进行二次开发,模拟研究了基质的弹性模量、抗拉强度、水平主应力差及压裂液排量等主要因素对水力裂缝长度和宽度的影响规律。结果表明:4个因素对水力裂缝长度和宽度的影响范围由大到小依次为压裂液排量、基质的弹性模量、基质的抗拉强度和水平主应力差;在压裂液排量一定时,水力裂缝长度随基质弹性模量、水平主应力差的增大而增大,随基质抗拉强度的增大而减小,宽度随基质弹性模量、水平主应力差的增大而减小,随基质抗拉强度的增大而增大;在弹性模量、抗拉强度和水平地应力差一定时,水力裂缝的长度和宽度均随着压裂液排量的增大而增大。研究结果可为干热岩热能的开发利用提供一定依据。

The permeability and connectivity of cracks in hot dry rock reservoir directly affect the heat transfer effect.Hydraulic fracturing is an important means to enhance the fracture characteristics.In order to master the fracture propagation law during hydraulic fracturing,this paper takes GR1 geothermal well in Gonghe Basin,Qinghai province at a depth of 3500~3705 meters as the research object.Through the secondary development of ABAQUS hydraulic fracturing simulation software,the effects of matrix elastic modulus,tensile strength,horizontal principal stress difference and fracturing fluid displacement on the length and width of hydraulic fractures were simulated and examined.The results show that the influence range of the four factors on the hydraulic fracture length and width in descending order is the fracturing fluid displacement,elastic modulus of the matrix,tensile strength of the matrix and horizontal principal stress difference.The length of hydraulic fracture increases with the increase of matrix elastic modulus and horizontal principal stress difference,and decreases with the increase of matrix tensile strength;the width decreases with the increase of matrix elastic modulus and horizontal principal stress difference,and increases with the increase of matrix tensile strength.And when the elastic modulus,tensile strength and horizontal ground stress difference are certain,the length and width of hydraulic fracture increase with the increase of fracturing fluid discharge.The research results can provide some basis for the exploitation and utilization of thermal energy of dry hot rock.