Core drilling technology for ultra thick sedimentary layers of ZC1 well in Sanlingwan, Zhangye, Gansu

The sedimentary strata has poor stability, and accidents such as shrinkage, collapse, block falling, and adsorption sticking are prone to occur. Conducting core drilling in sedimentary strata has always been a technical challenge in the drilling field. This article introduces the construction technology of core drilling in ultra thick sedimentary layers for the Zhangye geothermal core drilling project (ZC1 well) in Gansu Province. The various drilling techniques has been innovatively applied in this project, the research and application of flushing fluid systems, deep hole coring equipment, etc., are conducted, which solved the problems of borehole instability, adsorption sticking,drilling tool failure, and low drilling efficiency due to ultra thick sedimentary layers. It has formed a continuous core drilling process system for ultra thick sedimentary layers, providing reference for the subsequent drilling constructions in the similar complex formations.