为了阐明地应力非均质性和割理角度对煤层井壁稳定的影响,参考某地区基础物性、煤岩力学参数、割理宏微观结构及地应力状态,基于离散元数值模拟手段并结合最大位移和归一化塑性区域半径两种评价方法综合评价分析了地应力非均质性和割理角度对煤层井壁稳定的影响。数值模拟研究结果显示,在各向同性地应力条件下,割理角度对煤岩井壁稳定性的影响不大,随着地应力非均质性增大,割理角度对煤岩井壁稳定性的影响逐渐明显。随着割理角度的增加,井周最大位移有先增加后减小趋势。随着地应力非均质性的增加,由割理角度的变化产生的井周塑性区域半径各向异性越明显。因此在地应力差异较大的煤岩地层,不可忽视割理角度对井壁稳定的影响。研究成果可为研究区煤层直井及水平井的钻井方案设计提供参考。

In order to illustrate the influences of the in-situ stress heterogeneity and cleat angle on wellbore stability of coal seam, the following researches have been done. The basic physical properties, mechanical parameters, macro and micro structure of cleats and in-situ stress states of coal and rock in an area have been acquired. Based on the discrete element numerical simulation method, comprehensive evaluation and analysis of the in-situ stress heterogeneity and cleat angles on wellbore stability in coal seam has been conducted by two kinds of evaluation method i.e. the maximal displacement and normalized the plastic area radius. The results of the numerical simulation show that under the condition of isotropic in-situ stress, cleat angle has little influence on the borehole stability. With the increases of the heterogeneity of in-situ stress, the influence of cleat angle on borehole stability is becoming more and more obvious. The maximum displacement around the well increases first and then decreases with the increase of the cleat angle from 0° to 90°. Meanwhile, with the increase of in-situ stress heterogeneity, the anisotropy of the radius of the circumferential plastic area caused by the change of cleat angle becomes more obvious. Therefore, the influence of cleat angle on wellbore stability should not be ignored in coal and rock strata with great difference in in-situ stress. The research results can provide reference for the drilling plan design of vertical and horizontal wells of coal seam in the study area.