Solidifying Mud Cake to Improve Cementing Quality of Shale Gas Well: ACase Study

摘要

The purpose of this study is to improve the cementing quality of shale gas well by mud cake solidification, aswell as to provide the better annular isolation for its hydraulic fracturing development. Based on the self-establishedexperimental method and API RP 10, the effects of mud cake solidifiers on the shear strength at cement-interlayerinterface (SSCFI) were evaluated. After curing for 3, 7, 15 and 30 days, SSCFI was remarkably improved by 629.03%,222.37%, 241.43% and 273.33%, respectively, compared with the original technology. Moreover, the compatibilityamong the mud cake solidifier, cement slurry, drilling fluid and prepad fluid meets the safety requirements for cementingoperation. An application example in a shale gas well (Yuanye HF-1) was also presented. The high quality ratio ofcementing quality is 93.49% of the whole well section, while the unqualified ratio of adjacent well (Yuanba 9) is 84.46%.Moreover, the cementing quality of six gas-bearing reservoirs is high. This paper also discussed the mechanism of mudcake solidification. The reactions among H3AlO42- and H3SiO4- from alkali-dissolved reaction, Na+ and H3SiO4- in themud cake solidifiers, and Ca2+ and OH- from cement slurry form the natrolite and calcium silicate hydrate (C-S-H) withdifferent silicate-calcium ratio. Based on these, SSCFI and cementing quality were improved.