层理性地层井壁坍塌失稳规律研究

Research on Wellbore Collapse of Stratification Formation

渤海油田中深部地层微裂隙、节理和层理发育,基于传统完整性地层预测的坍塌压力不符合实际,需考虑强度各向异性的影响。鉴于此,基于弹性力学与结构面强度理论,假设地层中存在一组或两组低强度弱面,建立了井壁坍塌失稳预测模型,分析了单弱面与双弱面条件下坍塌压力随弱面倾角与走向的变化规律。分析结果表明:考虑弱面存在的地层坍塌压力远大于各向同性地层;单弱面下,坍塌压力最高值随井斜角增大从弱面倾角60°～90°逐步向45°～60°转化,定向井沿弱面反向坍塌压力最低,水平井沿弱面方位与相反方位坍塌压力值相同且均为最低值;双弱面下,2组弱面倾角夹角为0°时坍塌压力最低,坍塌压力最高值随井斜角增大从弱面倾角夹角60°～90°向30°～60°转化;走向夹角为0°时坍塌压力最低,定向井坍塌压力最大值出现于夹角90°～135°和270°～315°内,水平井走向夹角相差180°时坍塌压力相同且极大值与夹角无关。采用本预测模型对渤中构造深井进行了实例分析,井壁坍塌压力分析结果与实际情况比较接近,对现场作业有一定的指导意义。

The development micro-fractures, joints and bedding in the middle and deep strata of the Bohai Oilfield makes the collapse pressure predicted using conventional integrate formation not consistent with actual situation. The influence of the strength anisotropy should be considered. Based on the theory of elastic mechanics and structural plane strength, one and two sets of low-strength weak planes in the stratum are assumed, the prediction model of wellbore collapse is established. The effect of weak plane dip angle and direction on collapse pressure under single and two weak planes are analyzed. The analysis results show that the collapse pressure of the formation considering the weak plane is much larger than that of the isotropic formation. Under the single weak plane, with increase of the well inclination, the highest value of collapse pressure diverts from 60°~90° to 45°~60° of weak plane dip angle. The collapse pressure of the directional well against the weak plane is the lowest. The horizontal well has the same lowest collapsing pressure along and against the weak plane orientation. Under the two weak planes, the lowest collapse pressure is observed when the intersection angle between the two weak planes is 0°. With the increase of well inclination, the highest collapse pressure value diverts from the weak plane intersection angle of 60°~90° to 30°~60°. When the weak plane direction angle is 0°, the collapse pressure is the lowest. The maximum collapse pressure of the directional well is observed in the weak plane direction intersection angle of 90°~135° and 270°~315°. When the weak plane direction intersection angle of the horizontal wells is 180°, the collapse pressure is the same and is irrelevant with the intersection angle. The model is used to analyze the deep wells in the Bozhong structure, which results in consistent analysis results with the actual wellbore collapse pressure, which shows a guiding significance for the field operation.