渝东南页岩储层地应力计算方法

Calculation method for in-situ stress of shale reservoir in Southeast Chongqing

地应力是钻井和压裂改造的重要参数,而渝东南地区的页岩储层非均质性明显,各向同性地应力模型不适用于页岩地层,需要重新建立适合该类地层的地应力计算方法。为此,在页岩岩石力学特性的基础上,推导页岩横向各向同性的本构关系,并建立基于测井资料获取页岩横向各向同性力学参数的关系式,然后结合邻井水力压裂资料反演出该地区的构造应变系数,联合建立了页岩的横向各向同性地应力计算方法,利用该方法计算渝东南地区某页岩气井一段深度的地应力,将计算结果绘制出连续变化的地应力剖面图,最后通过该井3个深度点的声发射实验反演出对应深度的地应力值,并将其与计算结果进行对比验证。结果表明:①页岩横向各向同性特征明显,水平弹性模量普遍大于垂直弹性模量,水平和垂直泊松比差异小,无明显规律;②基于横向各向同性模型计算的最小水平地应力值高于各向同性模型计算的地应力值,其中基于横向各向同性模型的计算结果与岩石声发射的测量结果之间的相对误差均小于7%,平均为5.07%;③黄氏模型和组合弹簧模型的计算结果与岩石声发射测量结果的相对误差均大于15%。本文模型从页岩的构造特征出发,更符合地层的真实情况。

In-situ stress is an important parameter for drilling and fracturing reconstruction,but the shale reservoir heterogeneity in southeastern Chongqing is obvious,which makes the isotropic in-situ stress model unsuitable for shale formations,and it is necessary to re-establish a suitable stress calculation method for this type of formation.In response to the above problems,based on the mechanical properties of shale rock,this paper derives the lateral isotropic constitutive relationship of shale,and establishes a relational formula to obtain the lateral isotropic mechanical parameters of shale based on logging data.Also,combining the hydraulic fracturing data of adjacent wells,the structural strain coefficient of the area is reversed,and a method for calculating the horizontal isotropic in-situ stress of shale is jointly established.Using this method to calculate the in-situ stress at a depth of a shale gas well in the southeastern Chongqing,the calculation results were drawn into a continuously changing stress cross-section graph.The changing in-situ stress profile,and finally the inversion of the in-situ stress value at the corresponding depth through the acoustic emission experiments at the three depth points of the well are verified by the comparison with the calculation results.The results show that①The horizontal isotropy of shale is obvious,the horizontal elastic modulus is generally greater than the vertical elastic modulus,the difference between the horizontal and vertical Poisson’s ratio is small,and there is no obvious rule;②The minimum horizontal in-situ stress calculated based on the lateral isotropic model is higher than the in-situ stress value calculated by the isotropic model,where the relative error between the calculation results based on the lateral isotropic model and the measurement results of the rock acoustic emission is less than 7%,with an average of 5.07%;③The relative error between the calculation results of the combined spring model and the rock acoustic emission measurement results is greater than 15%.In this paper,the model is based on the structural characteristics of shale,which is more in line with the real situation of the formation.