由井壁崩落宽度反演地层水平主应力的数学模型

Mathematical Model for Deriving Formation Horizontal Stress from Sidewall Breakout Width

对井壁剪切破坏崩落规律的研究发现,井壁崩落扇形区域面积不受多次崩落影响,基本为定值,可通过4臂或6臂井径测井获取。以此规律为基础,基于线弹性理论,建立了井壁发生初次破坏崩落的数学模型。利用该模型,在已知最小水平主应力、岩石内摩擦角、内聚力、地层孔隙压力、钻井液柱压力和井壁崩落扇形区域面积一定的条件下,可反算出最大水平主应力。研究表明,模型计算结果与室内实验值十分接近,该模型简单实用、精度较高。

It was found out that the sidewall breakout width is generally fixed and not influenced by multiple breakouts,which can be acquired by four and/or six calipers logging.Base on the fact and using linear elasticity theory,this paper develops the mathematical model for initial sidewall breakout,by which the maximum horizontal principal stress can be back calculated,if given the minimum horizontal stress,rock internal friction angle,coherence,pore pressure,mud fluid pressure and sidewall breakout width.The study indicates that the result computed by the theoretical model is closed to the core lab data,and the model is easy for use and has higher accuracy.