适用于煤层气钻井的微泡沫钻井液研究

Research on micro-foam drilling fluid suitable for coalbed methane drilling

煤储层具有低压、低渗、微裂缝发育等特点,在煤层气开采过程中容易对储层造成损害,降低煤层气井产量。针对此问题,笔者进行了起泡剂分子结构设计并合成了一种新型高效双子型起泡剂,同时以该起泡剂为基础,构建了适用于煤层气钻井的微泡沫钻井液体系。通过实验分析了煤岩组成、煤岩微观结构与煤层顶底板岩样性质,并评价了微泡沫钻井液对煤系地层的适用性。结果表明:新型起泡剂性能良好,能够显著降低水的表面张力,当质量分数为0.1%时,降幅可达71.82%;半衰期是常规起泡剂的3倍以上,稳泡性能良好;采用接触角测定仪测试了新型起泡剂对煤岩润湿性的影响,表明新型起泡剂对煤岩润湿性改变程度小,煤岩接触角恢复率达86%,有利于提高煤层保护效果。微泡沫钻井液体系黏度适中,流变性能良好,动塑比高,携岩能力强,泡沫质量稳定,其微观形态测试结果表明微泡沫的水化膜较厚,具有较强稳定性,微泡沫粒径呈现正态分布,平均粒径为144μm,半衰期>82 h。煤层顶底板岩样在微泡沫钻井液中的线性膨胀率小于3%,滚动回收率大于92%,表明微泡沫钻井液具有良好的抑制能力,能够维持煤层顶底板地层的井壁稳定性。煤芯气测渗透率恢复率达到90%以上,具有良好的储层保护效果,能够满足低压低渗煤层的钻井要求。通过建立钻井液中处理剂解吸附评价实验装置与方法,评价了微泡沫钻井液中处理剂的解吸附能力,结果表明微泡沫钻井液中处理剂吸附量小,易于脱附,在煤岩中脱附率达82.4%。基于新型双子型起泡剂的微泡沫钻井液能够有效维持煤层顶底板岩样的井壁稳定性,并能在煤层表面易于脱附,提高了对煤储层的保护效果,适用于煤层气钻井作业。

Coal reservoirs have the characteristics of low pressure,low permeability and micro-crack development.In the process of coalbed methane exploitation,it is easy to cause damage to the coal reservoir and reduce the production of coalbed methane wells.In terms of these problems,the molecular structure of a new type of high-efficiency gemini foaming agent was designed and the foaming agent was synthesized in the laboratory.At the same time,based on the gemini foaming agent,a micro-foam drilling fluid system suitable for coalbed methane drilling was developed through some experiments.The coal rock composition,micro-structure and properties of coal seams roof and floor rock samples were analyzed,and the applicability of micro-foam drilling fluid to coal seams and coal seams roof and floor rock samples were evaluated by laboratory experiments.The research results indicate that the new foaming agent has good performance property,thus,it can significantly reduce the surface tension of water.When the foaming agent concentration is 0.1%,the drop rate of water can reach 71.82%.The half-life period of the new gemini foaming agent is 3 times more than that of the conventional foaming agent,and the performance of the stable foaming film is good.Furthermore,the effect of new foaming agent on the wettability of coal rock samples were studied by contact angle measuring instrument.The results show that the new foaming agent has little change to the wettability of coal rock,and the recovery value of coal rock contact angle is 86%,which is beneficial to improve the protection effect of coal seam.The micro-foam drilling fluid system has the characteristics of moderate viscosity,good rheological property,high dynamic plastic ratio and stable foam quality.These characteristics can improve the cuttings-carried ability of micro-foam drilling fluid.The results of foam micro-morphology test show that the hydrated film of micro-foam drilling fluid system is thicker and has strong stability,the micro-foam particle size exhibits a normal distribution with an average bubble size of 144 μm and the half-life period is more than 82 h.The linear expansion rate of the coal seam roof and floor rock sample in the micro-foam drilling fluid is less than 3%,and the rolling recovery rate is greater than 92%,indicating that the micro-foam drilling fluid has a good inhibition ability and can maintain the wellbore stability of the coal seam roof and floor formation.The recovery rate of coal core gas permeability is over 90%,which has good reservoir protection effect and can meet the drilling requirements of low pressure and low permeability coal seam.The adsorption and desorption ability of the treatment agents in the micro-foam drilling fluid were evaluated by establishing the experimental device and method.Adsorption and desorption experiments show that the micro-foam drilling fluid has small adsorption capacity and easy desorption,and the desorption rate in coal rock sample is 82.4%.The micro-foam drilling fluid based on the new gemini foaming agent can effectively maintain the wellbore stability of the coal seams roof and floor rock samples,desorb easily on the surface of the coal seam sample,improve the protection effect on coal reservoirs.Therefore,it is suitable for coalbed methane drilling operations.