利用斜井井壁破坏信息计算最大水平地应力

准确获取深部地层的地应力大小和方向,对于安全钻井作业、控制井筒出砂和压裂增产至关重要。利用井壁破坏信息计算地应力的方法已得到广泛认同,甚至已建立了利用井壁崩落宽度计算最大水平地应力的模型,但是该计算模型仅限于直井井壁破坏。为此,根据线性多孔弹性岩石力学理论,确定了任意斜井井壁崩落位置和张性裂缝位置,找出了间接计算最大水平地应力的方法,即利用斜井井壁崩落和张性裂缝建立地应力和岩石强度的关系图版,根据实际岩石强度确定最大水平地应力。利用该方法对川西南部斜井成像测井观测到的井壁破坏信息进行了实例分析,分析结果表明,该地区垂深4 663.5 m处的最大水平地应力为178.9~180.3 MPa。川西南部地区正处于逆断层地应力状态,在较强的水平挤压应力作用下,该地区的原生断层接近摩擦极限应力状态,断层容易滑动,因此该地区地震频发。利用该方法可以根据任意斜井井壁的破坏情况计算最大水平地应力,扩展了斜井成像测井资料的应用范围。

Calculation of maximum horizontal stress using failure information of inclined wellbore

Accurate knowledge of the magnitude and direction of stress at depth is important for the safety of drilling operations,sand control and fracturing stimulation.The method of using the failure information of wellbore to determine the stress has been widely recognized,and even a model to calculate the magnitude of the maximum horizontal stress using the breakout width of wellbore has been built,but the model is limited to vertical wells.Therefore,according to the linear poroelastic rock mechanics theory,the positions of breakout and tensile fracture of arbitrary inclined wellbore are determined,and an indirect calculation method of the maximum horizontal stress is proposed in this paper,namely,using the breakout and tensile fracture from inclined wellbore to establish the relation chart between in-situ stress and rock strength and using the actual rock strength to determine the maximum horizontal stress.The failure observed from the image logging of an inclined wellbore in Southwest Sichuan is analyzed by using this method and the results show that the maximum horizontal stress at vertical depth of 4 663.5 m in this area is 178.9-180.3 MPa.Southwest Sichuan is in reverse faulting stress state and the primary fault has reached friction limit state under the strong horizontal compressive stress and is prone to slip,so earthquake is frequent in this area.This method can be used for calculating the magnitude of the maximum horizontal stress based on the failure information of any inclined wellbore,which will extend the application scope of imaging logging data of inclined wellbore.