沁水盆地煤层气井坍塌压力预测

Prediction of collapse pressure for CBM wells in Qinshui CBM fields

张公社 李永康 尹俊禄 唐文英 崔金榜 程浩

ZHANG Gongshe LI Yongkang YIN Junlu TANG Wenying CUI Jinbang CHENG Hao

长江大学，湖北荆州　434023 华北油田公司地球物理勘探研究院，河北任丘　062552 华北油田公司采油工艺研究院，河北任丘　062552

School of Petroleum Engineering, Yangtze University, Jingzhou 434023, China Research Institute of Geophysical Prospecting, Huabei Oilfield Company, Renqiu 062552, China Research Institute of Oil Production Technology, Huabei Oilfield Company, Renqiu 062552, China

针对煤层气井井壁稳定问题，应用力学分析方法从井壁应力分布入手，根据斜井井壁稳定力学模型，分别结合Mohr-Coulomb准则和Drucker-Prager准则，建立水平井筒井壁坍塌压力计算公式。应用所建立的公式对沁水3#煤层羽状水平井坍塌压力进行了预测。计算结果表明，井眼沿最大水平主应力方向时，坍塌压力为负值，这种情况下煤层气井不会坍塌，井眼稳定；当井眼沿最小主应力方向时，坍塌压力高于或者略低于地层压力，说明煤层羽状井眼不稳定，会产生煤粉；当井眼介于最大和最小水平主应力之间时，其坍塌压力在所计算的两个压力之间。

In order to solve the wellbore stability problems of coalbed methane（CBM）wells, a formula for calculating the collapse pressure for the horizontal well was established, using the mechanical methods to analyze the stress distribution of sidewell and separately adapting the Mohr-Coulomb strength criteria and the Drucker-Prager strength criteria to the direction well stability model. The formula is used to forecast the collapse pressure for the pinnate horizontal well in Qinshui 3# CBM fields. The results show that the wellhole is stable when it is in the direction of the maximal horizontal stress, in which case is that the collapse pressure of minus value; the wellhole is unstable when it is in the direction of the minimal horizontal stress, in which case is that the collapse pressure more than or a little less than the formation pressure,meaning it may cause coal dust; the collapse pressure is between the two when the wellhole is in the direction between the directions of the maximal horizontal stress and the minimal horizontal stress.