With the exploration and development of hydrocarbon reservoirs moving toward more complex formation, downhole vibrations have been identified as one of the most significant limiters to improve the rate of penetration (ROP) and bit footage. Thus, great efforts have been put on the development of cost-effective technologies and special vibration mitigation tools in order to achieve high rock breaking efficiency. The paper introduces the development and application of optimizer of drilling operating parameters named as Smart Driller Indicator (SDI) by real-time stick/slip severity monitoing based on an innovative ROP and Mechanical Specific Energy (MSE) optimization algorithm. In addition, the drillstring mechanics model establishment anlalyzing torsional vibration and field application results of the system are elaborately description.
The optimization algorithm is a drlling performance improvement algotithm on basis of MSE theory. From the perspectives of rock mechanics and conservation of energy, the ideal performance in the optional proportion among drilling parameters, ROP and MSE have been derived from comprehensive analysis of optimized drilling mechanism. Based on Newton's equation of motion, an advanced damped forced torsional vibrarion estimate (TSE) model in frenquency-domain was developed. The vibration model achieves higher accuracy diagnosis and computational efficiency due to more boundary condition effects combined with a fit-for-purpose rigid model, damping coefficient algorithm and BHA-matching transfer matrices. The model supports real-time downhole vibration surveillance as well as pre-drill BHA evaluation and post-drill root cause analysis. Additionally, the vibration mitigation principle is demonstrated in detail, conducting a variety of tests to mitigate downhole torsional vibration. SDI can diagnose the inducing factors of downhole vibration, providing useful insights into the judgment of reasonability of drilling parameters.
A three-week pilot test has been conducted in deep wells in Yumen Oilfield in China, with 30% increase of the average ROP and 40% enhancement of the average bit footage compared with offset wells. Application of SDI to enhance ROP efficiency is not affected by well type, formation and bottom- hole temperature; thus, it could be widely applied in any drilling conditions.