有效提高页岩气井固井质量的泥饼固化防窜固井技术

X2井是湖北某盆地的一口重点页岩气评价井。为解决该区域存在的φ139.7 mm生产套管固井前钻井井漏严重、井径极其不规则、固井质量难以保证后续储层体积压裂作业等问题,在室内评价实验的基础上,决定使用泥饼固化(MCS,Mud Cake Solidification)防窜固井技术。该项技术的机理是把泥饼固化剂放在先导水泥浆之前注入,通过其与井壁泥饼接触并进行一系列化学反应,形成的胶凝物质对泥饼中的各物质进行填充和黏接,相互胶结形成致密的固结体,进而实现固井二界面泥饼固化。X2井的现场应用效果表明:声波一变密度测井(CBL/VDL)解释结果第一界面固井质量胶结好的占91.4%,胶结中等的占8.3%,胶结差的占0.3%;第二界面固井质量胶结好的占29.4%,胶结中等的占70.6%,胶结差的占比为0,综合评价为优质,较邻井(X1井)固井质量大幅度提高;X2井经初步压裂,测试获得页岩气产量900 m~3/d。充分说明了MCS技术不但可显著提高复杂井界面胶结质量和层间封隔效果,满足页岩气体积压裂的需要,而且还能避免因顶替效率低、界面胶结质量差而导致的测井质量差和潜伏的环空气窜问题。

Mud cake solidification technology for improving cementing quality of shale gas wells

The Well X2, located in a certain basin in Hubei province, is an important shale gas appraisal well. In order to solve such problems as the serious lost circulation at 139.7 mm production casing before well cementation and highly irregular borehole, and to ensure a qualified cementing quality for the subsequent stimulated reservoir volume (SRV) fracturing, we employed the Mud Cake Solidification (MCS) technology in this well to prevent channeling on the basis of laboratory evaluation and experiment. In this program, MCS agents are pumped before cement slurry is injected. A series of chemical reactions take place when MCS agents contact with wall mud cakes, generating gels with which the pores and micro-fractures of mud cakes are filled and bonded. In this way, cumulates are formed and mud cakes at cement-formation interface are solidified. Based on the interpretation results of CBL/VDL well logging in Well X2, the ratios of good cementation, medium cementation and poor cementation at cement-casing interface are 91.4%, 8.3% and 0.3% respectively, and those at cement-formation interface are 29.4%, 70.6% and 0 respectively. On the whole, therefore, its cementing quality is evaluated as high level and much better than that of its adjacent well (Well X1). After preliminary fracturing, the production rate of shale gas is 900 m³/d. It is shown that MCS technology can not only ensure interface cementation and zonal isolation for SRV fracturing, but avoid latent annulus gas channeling and poor logging quality caused by low displacement efficiency and poor interface bonding.