“三强”防塌钻井液的研究与应用

通过对四川地区地层失稳的机理分析,认为失稳主要由以下原因造成:地层中的泥页岩吸水膨胀造成井壁失稳；地层中存在众多纵横交错的裂缝、微裂缝,裂缝、微裂缝吸水引起应力失衡,或者地层因受到频繁的拉伸和挤压作用形成破碎带,在破碎带地层泥页岩吸水膨胀和应力失衡同时存在,造成井壁失稳.针对井壁失稳的原因,采取了包被、抑制和封堵相结合的方法,经过室内实验优选出“三强”(强包被、强抑制、强封堵)防塌钻井液.该体系通过现场20多口井的应用,解决了气液转换过程中出现的垮塌和正常钻进中的井壁稳定问题,使用的钻井液密度最高达到2.20 g/cm3,其抑制能力高于7％氯化钾溶液,封堵能力强于普通封堵钻井液,可在不同地区不同密度下使用,适应性强.

Research and Application of "Three Strong" Anti-caving Drilling Fluid

In this paper,the mechanism of caving in Sichuan is analyzed that are hydration swelling of clay stone,overbalancestress caused by hydration of cross-fractures,and crushed zone formed of frequent extension and compression.Based on themechanism,the "Three Strong" drilling fluid system,which has strong performances of encapsulating inhibition and sealing,is developed.The applications of more than 20 wells show that,the difficult in process of gas/liquid transformation of cavingis overcome by using this drilling fluid system,and that of the highest density is 2.20 g/cm3,which the inhibitive performanceis stronger than 7%KC1 solution and the sealing performance is better than normal sealing drilling fluid system.