钻井液润湿性影响页岩井壁稳定性的实验研究

煤层气井单井产量往往较低,综合勘探开发煤系非常规天然气是提高煤层气开发效益的重要途径,但这要求钻井液能同时解决煤层、致密砂岩和页岩地层的井壁稳定问题。为此,提出基于"正电性-中性润湿-化学抑制-纳米材料封堵-合理密度支撑"的协同防塌理论,并开展了钻井液润湿性影响页岩井壁稳定性的实验工作。首先优选出能有效降低钻井液表面张力、增加钻井液与页岩接触角的表面活性剂复配方案,并结合钻井液流变性、滤失性、润滑性、水活度和抑制性等参数测试和页岩压力传递实验,对钻井液润湿性影响页岩井壁稳定性的效果进行了评价。结果表明:复合表面活性剂能够有效改变水基钻井液的润湿性能,与优选的水基钻井液相比,钻井液表面张力降低42.6%,与页岩的接触角增大162.1%;复合表面活性剂与水基钻井液具有良好的配伍性,具有较好地抑制性和抗盐能力;与清水相比,复合表面活性剂能显著阻缓页岩孔隙压力传递速率,降低钻井液侵入页岩的程度,页岩渗透率降低幅度在99%以上;说明通过控制钻井液润湿性来增强页岩井壁稳定性是可行的。

Experimental study on the effect of drilling fluid wettability on shale wellbore stability

The output of single coalbed methane (CBM) well is rather low,and the comprehensive exploration and development of unconventional natural gas of coal measures is an important technical approach for improving the development benefits of CBM.However,this requires that the drilling fluid can solve the wellbore stability problem in coal,tight sandstone and shale strata together.Therefore,the authors proposed a cooperative anti-collapse theory based on positive electricity,neutral wetting,chemical inhibition,nanoparticles plugging and support of reasonable density,and carried out the experimental work on the influence of drilling fluid wettability on shale wellbore stability.Firstly,the authors optimized the compound formulation that could effectively reduce the surface tension of drilling fluid and increase the contact angle between drilling fluid and shale.Then,combined with the evaluation of drilling fluid viscosity,filtration,lubrication,water activity and inhibition,and the pressure transmission tests of shale,the effect of drilling fluid wettability on wellbore stability of shale was evaluated.The results show that,compared to optimized water based drilling fluid,the compound surfactants could effectively change its wettability,the surface tension of drilling fluid is reduced by 42.6%,and the contact angle to the shale is increased by 162.1%.In addition,the compound surfactants have a good compatibility with water-based drilling fluid and a certain salt resistance.In contrast with water,the compound surfactants could effectively retarded the transmission of shale pore pressure,decrease the degree of the invasion of drilling fluid into shale,and reduce the permeability of the shale with a rate up 99%.Therefore,it is possible to improve wellbore stability of shale by controlling drilling fluid’s wettability.