煤层气井井斜角对隔水层界面胶结强度影响试验

Experimental study on the influence of well inclination angle of coalbed methane well on the cementation strength of cement-formation interface

为了控制煤层气井开采过程中的水窜问题,采用自主设计的试验装置对沁水盆地晋城地区煤层气样品进行模拟试验,获得了井斜角分别为0°、30°、60°、90°条件下隔水层界面胶结强度试验数据,分析了井斜角对隔水层界面胶结强度的影响机理。结果表明:隔水层界面胶结强度随井斜角的增大而降低,原因是随着井斜角增大,井壁的泥饼环上部依次变薄,下部依次变厚,井斜角到90°时达到最厚,且随着泥饼的变厚,泥饼成分中黏土矿物的成分逐渐减少,钻屑和重晶石的含量逐渐增多。分析还认为,影响隔水层界面胶结强度主要因素有黏聚力、泥饼的含水率、颗粒密实程度、颗粒结构和矿物成分。因此,煤层气井型对隔水层界面胶结强度的影响较大,即若采用水平井开采煤层气,可能水窜问题更突出。

In order to control the problem of water channeling in the process of coalbed methane(CBM)production,based on the self-designed test device and method,the test data of the shear strength at cement-aquiclude interface(CAI)is obtained under the conditions of well inclination of 0°,30°,60°and 90°.The mechanism of the influence of inclination angle on the shear strength at CAI is analyzed.The results show that the shear strength at CAI de-creases with the increase of the inclination angle.The reason is that as the inclination angle increases,the upper part of the mud cake ring becomes thinner in turn,and the lower part becomes thicker in turn.When the inclination angle is 90°,the mud cake is thickest.As the mud cake thickens,the clay minerals in the mud cake is decreasing,and the content of drill cuttings and barite increase.Through the analysis it is also believed that the main factors affecting the shear strength at CAI are cohesion,moisture content,grain compaction,particle structure and mineral composition in the mud cake.Therefore,the CBM well type has a great influence on the hear strength at CAI.If the horizontal well is used to extract CBM,the problem of water channeling may be more prominent.