With the exploration and development of hydrocarbon reservoirs moving toward deeper and more complex formation in China, the great hardness and high abrasiveness of carbonate formation bring out great challenges of improving the rate of penetration (ROP). Great efforts have been put on the development of cost-effective technologies and tools. This paper introduced the development and application of the optimized drilling system, based on the mechanical specific energy (MSE) theory, and elaborated the optimized mechanism analysis, optimized model establishement and field applications results of the system. From the perspectives of energy balance principle, the relationship between drilling parameters and ROP has been derived from the compreshensive analysis of rock breaking mechanism. Based on the R.Teale MSE model, the results are more accurate by introducing the bit-specific coefficient of sliding friction and the energy transmission effect. In view of the differences in calculating specific energy of other drilling methods, related model was proposed for compound drilling. Besides, to be used as peak efficiency baseline, confined compressive strength (CCS) model was inferred with Skempton pore pressure model. Finally, the optimized principle was constructed for the drillers, conducting a variety of tests to optimize performance. Optimization provides the ability to diagnose the limiters influencing drilling efficiency, and gives useful insights into the judgment of reasonability of drilling parameters. A two-month pilot in Tarim Basin has been conducted, in which the average ROP was increased by 30% and the average bit footage was enhanced by 40% compared with offset wells. The system was not affected by well type, formation and bottom-hole temperature; thus, it could be in continuous operation. As an effective tool for further excavating the potential of ROP, the optimized drilling system might achieve satisfactory outcomes that overcome the drilling challenges of carbonate formation, igneous rocks and shale in China.
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