砂泥岩地层地应力纵向分布特征与规律

以实际沉积地层中抽象出来的砂泥岩地层概念模型为研究对象, 在盆地构造力学、岩石力学性质分析的基础上, 采用应力场数值模拟法研究分析砂泥岩地层中的纵向地应力分布特征和规律。研究结果表明, 水平主应力在砂泥岩的分界面发生突变, 变化程度主要与两侧岩石的力学性质差异相关, 也与区域构造应力有一定关联; 杨氏模量对最大水平主应力影响程度大于对最小水平主应力的影响, 泊松比对地层最小水平主应力影响程度大于对最大水平主应力的影响。杨氏模量和泊松比对最大水平主应力的影响, 在伸展应力状态下前者影响相对较小, 走滑应力状态下, 影响程度基本相同, 挤压应力状态下, 前者影响程度相对较大; 而对于最小水平主应力的影响, 在三种应力状态下, 泊松比的影响均大于杨氏模量。地层的岩性变化方式(渐变或突变)对地层最小水平应力差产生显著影响, 厚度变化对地层最小水平应力差大小无影响。上述认识可以指导砂泥岩地层的压裂和储层改造, 改善压裂效果。 

CHARACTERISTICS AND REGULARITY OF LONGITUDINAL GEOSTRESS DISTRIBUTION IN SAND-MUDSTONE STRATA

Based on the analysis of basin geomechanics and mechanical properties of rocks, the characteristics and regularity of geostress distribution in the sand-mudstone strata are studied with numerical modeling by using the conceptual model of sand-mudstone strata abstracted from actual sedimentary strata. The results showed that horizontal principal stress mutates at the interface of sand-mudstone strata, and the change degree is mainly related to the difference of mechanical property of rock on both sides, then the regional tectonic stress. The effect of Young Modulus on the horizontal maximum principal stress is greater than that on the horizontal minimum principal stress; while the effect of Poisson Ratio on the horizontal minimum principal stress is higher than that on the horizontal maximum principal stress. The effect of Young Modulus and Possion Ratio on the horizontal maximum principal stress is different in different stress state. In extensional strike-slip and compressional stress state, Possion Ratio has greater roughly equivalent and samller effect on the horizontal maximum principal stress respectively. While, the effect of Possion Ratio on the horizontal minimum principal stress is always greater than that of Young Modulus in different stress state. The way of lithology changes in strata (mutations or gradient) has remarkable influence on the stress difference of horizontal principal stress, while the thicknesses no effect. The above understanding is valuable for effective reservoir hydraulic fracturing and reformation.