The design of drilling tools for deep wells requires a minimum knowledge of petrophysical and mechanical properties of the reservoir, but also of the overburden formations in case of difficult drilling. A specific working method was developed in the rock mechanics lab of the University of Mons (Belgium) to obtain maximum geomechanical characteristics from a small piece of rock. A large number of samples have been processed for a global oil and gas service company which develops drilling bits. The typical analysis includes a petrographical description, petrophysical characterization, mechanical tests (punching, uniaxial compression…) to draw mechanical properties, and abrasiveness test (FPMs method). A database is created to emphasize the potential driving parameters in understanding the wear behavior and cutting efficiency of drill bits. We present the working method and some results obtained from the data analysis and their relationship with the measured abrasiveness.
When drilling in difficult conditions, an appropriate bit design requires particular care in assessing mechanical and petrographic properties of drilled formations (reservoir and overburden). In addition, those characterizations have generally to be done from a small amount of rock material, which implies a specific testing program based on few or even non-destructive techniques. This particular methodology, coupled with the long-term collaboration with Halliburton's drill bits and core heads design and development team, involved the processing of a large number of samples and led to the development of a database in order to manage all the collected data and, especially, assess abrasiveness and its relation with other properties.
2 Presentation of the Database
The information collected from laboratory tests in the framework of the collaboration between UMONS and Halliburton has been gathered on a long time period, more than fifteen years, and deals with tests on core samples coming from all over the World (Algeria, Argentina, Australia, France, Germany, Japan, Norway, Oman, Poland, Russia, Saudi Arabia, USA, Venezuela,…). In this context, the collected data are generally associated with difficult drilling conditions for which specific analyses were required in order to explain the wear and improve the performance of the drilling tools. Therefore the tested rock samples are not statistically representative of geological conditions encountered in oil and gas drilling. In addition, the long time period over which data have been accumulated implies that different people have worked, sometimes with different methodologies (technical progress, new laboratory equipments). This required a consolidation of the data.