焦石坝地区页岩气水平钻井井壁稳定性实验研究

为揭示涪陵焦石坝地区页岩储层井壁岩石垮塌失稳诱因,探索页岩气水平井井壁垮塌主要控制因素,应用室内力学实验测试方法,研究了井下应力环境下页岩岩体力学空间各向异性及层理缝面力学性质,并结合焦页1HF井水平井实钻井下复杂情况,探讨了页岩的独特力学特性及其影响井壁岩石垮塌失稳的力学机理。实验结果表明:焦石坝页岩岩体平行层理极为发育,层理缝面间力学强度弱,沿层理走向的页岩剪切强度远低于垂直层理走向;焦石坝地区页岩具有极强的力学参数各向异性,页岩的力学参数变化与取心方向密切相关,当取心方向与层理法向夹角β满足β=0°和β=90°时,页岩力学强度最高,在30°β90°范围内,页岩力学强度呈先减小后增加的趋势,β=60°时,页岩力学强度最低。该研究成功解释了涪陵焦石坝地区页岩水平钻井井壁岩石垮塌失稳的力学主控因素,为焦石坝地区页岩气水平钻井井身结构及工程参数优化设计奠定基础,具有较高的现场应用价值。

Experimental Study on Wellbore Stability of Shale Gas Reservoir for Horizontal Well in Jiaoshiba Area

To reveal the collapse mechanism of shale gas reservoirs drilled with horizontal wells in Jiaoshiba area and find the main controlling factors of wellbore collapse of shale reservoirs,the rock mechanics anisotropy and the mechanical properties between bedding planes of shale reservoirs in the condition of down-hole stresses were studied with the mechanics expe6mental methods,and the unique mechanical properties of shale rock and its effect on wellbore instability were evaluated combined with the actual working conditions of horizontal well in well Jiaoye 1HF.The experimental results showed that,the shale rock in Jiaoshiba area contains a large number of horizontal bedding fractures which display lower mechanical strength properties,and the shear strength of rocks along the bedding planes is much weaker than that perpendicular to bedding planes.The shale rocks have a strong anisotropy of mechanical parameters,and the variation of mechanical parameters is closely related with coring direction in shale rocks.The rock strength attains the highest value while the angle between coring direction and normal direction of bedding planes equal to 0° or 90°,the rock mechanical strengths reduce firstly and increase in the range of 30° to 90°,and the mechanical strength is lowest while the angle meets 60°.This paper successfully explain the main controlling factors for the wellbore instability of shale reservoirs drilled with horizontal well in Jiaoshiba area,supplies the optimizationdesign technology for well construction and engineering parameters,which had leading practical value.