Research on application and optimal design of wireline core drilling bits for mudstone and shale

Abstract:

The research was supported by the shale gas survey well project in the middle and lower reaches of the Yangtze River， where wireline core drilling technology was used， and the formation encountered were mostly water-sensitive mudstone formations with high shale content， and dense formation with frequent soft and hard interbeds. In order to solve the problems of that bit balling of diamond drill bits and teeth breaking of PDC bits in soft and hard interlayers， which seriously affects the drilling speed and life of the drill bit， the article systematically analyzes the causes of diamond bit balling and PDC teeth breaking from the aspects of the bit structure and drilling fluid performance with respect to the field application results. It is noted that the above-mentioned problems arising from the field use of the drill bit are closely related to the design of the bit lip surface structure， the design of the bit waterway， the bit material and its surface condition，the drilling parameters and the performance of the drilling fluid. With examination of the drilling process and lithology， the structure was optimized and the design was improved of the existing drill bit， and the drilling parameters were also optimized. The results showed that the field drilling speed has been significantly increased， greatly improving the drilling efficiency over the mudstone section and the interlayer.