RasGas Company Ltd Drilling Task Force has instituted a new work process from ExxonMobil Development Company. This process is designed to optimize rate of penetration (ROP) in every foot of hole drilled. ROP limiters are systematically identified and eliminated during the drilling design, as well as during real-time well site operations.
A central element in this work process is the real-time display and analysis of Mechanical Specific Energy (MSE).MSE is the calculated work that is being performed to destroy a given volume of rock. When a bit is operating at its peak efficiency, the ratio of energy to rock volume will remain relatively constant. This relationship is used operationally by observing whether the MSE changes while adjusting drilling parameters such as weight on bit (WOB) or rotary speed (RPM).If it remains constant while increasing WOB, the bit is assumed to still be efficient. If the MSE ratio increases significantly, either while drilling or while adjusting parameters, the bit has foundered. The driller then determines the most likely cause of founder and adjusts parameters accordingly. Adjustments continue to be made until the MSE value is minimized. The process of adjusting parameters is referred to as MSE testing. Recorded results of the driller's MSE tests are also used in post-analysis to guide redesign of the drilling system when ROP limiters are beyond the driller's control. In the North Field operations, downhole vibrations data were coupled with the MSE curves to further enhance the interpretation of the cause of founder and to manage drilling parameters.
This paper presents examples from Qatar operations that demonstrate the manner in which MSE and vibrational data were used at the rig site to make operational decisions, and in post-drill analysis to redesign the system. Performance data is also provided to show the impact on operations. Performance improvements have varied by hole size, but range from 60 – 380%.
