Analysis and treatment of hole wall collapse of wire-line core drilling in pulverized coal strata

Abstract:

Duiring the construction of ZK30-1 hole， a detailed investigation hole for coal resources in Guojiatai， Jingtai County， Gansu Province， serious collapse accidents happened in the long hole section caused by forcibly lifting the “water drill”. In this paper， the main reasons why the hole wall collapse were analyzed. Large cumulative coal thickness exists in the collapsed strata， loose and broken surrounding rock structure are the geological factors. The mismatch between the performance of the flushing fluid and the lithology of the formation is the main technical factor. By introducing low viscosity and strong suppression flushing fluid， gently pressing and slowly rotating during the hole cleaning process， and circulating with small pump volume， the collapse of the hole wall was restored， and the hole was successfully finished. Coal drilling construction has strict requirements for flushing fluid performance， and more strict when wire-line core drilling was used to extract core powder. It is necessary to strengthen monitoring of flushing fluid performance changes during mud preparation and drilling processes.

Key words:wire-line core drilling;pulverized coal formation;hole wall collapse;hole scanning;flushing fluid performance;coalfield drilling