| The formation of ZK001 well is a large section of mudstone, and the local formation is a salt mudstone and a salt gypsum layer. Shale formation has strong water sensitivity, which is easy to cause the drilling fluid clay contamination, borehole instability, bit balling and other issues; The deep salt mudstone and salt bed have strong characteristics of water-soluble and creep property, easily lead to the expansion of well diameter and core corrosion. In this paper, taking well ZK001, for example, it has solved the problems such as formation strong mud making, instability of salt bed and borehole diameter enlargement by optimizing drilling fluid system and on-site construction process. With the help of the rock mechanics test, mineral identification, cation exchange capacity test, drilling fluid system optimization and performance testing ,it was determined to use polymer drilling fluid system in the upper formation ,and translate it into saturated salt water drilling fluid system before deep salt coring drilling. Selecting proper drilling fluid performance parameter in field work could effectively prevent the slurry making in upper mudstone formations and avoid creep and borehole diameter enlargement in salt bed formations. The performance of drilling fluid is stable and easy to be maintained, which ensures the safety and high efficiency of drilling, which provides a reliable guarantee for the successful completion of the coring task. |
