Structure design of weight-on-bit self-adjusting PDC bit based on stress field analysis and experiment evaluation

Abstract The complex formations such as soft-hard interbedded and strong abrasive strata in ultra-deep wells make the PDC bit inefficient in rock-breaking, which greatly increases the development cost of oil and gas reservoirs. There are two basic ways to solve the above problems: one way is to relieve the force condition of the bit by changing the working mode and the other is to release the stress of the rock at bottomhole with special tools. A method is proposed in this paper to make full use of the stress-releasing effect to reduce the value of compressive stress of the rock at bottom hole, even turn it into partially tensile stress, and take advantage of the cutting method of ‘Hybrid Bits’ to improve rock-breaking efficiency (RBE). A supporting Weight-on-bit (WOB) Self-adjusting Dual-diameter PDC Bit (WSADB) is invented to realize the above idea. Based on Biot's theory of poroelasticity and considering the fluid-solid coupling effect, numerical calculation of the stress field at well bottom is performed. The results show that the WSADB can improve the RBE by enlarging the volume of the stress unloading area at well bottom; The rock damage function based on the 3D Mohr-Coulomb Criterion is used to analyze the effect of structural parameters of the bit on RBE and the optimal structural parameters are obtained. When the diameter ratio of the pilot bit to the reaming bit is 0.5, the rock to be drilled at the well bottom will be damaged to the greatest extent; When the length of the pilot bit is longer than 0.5 times of the borehole diameter, the longer the length is, the greater the degree of damage to the rock at well bottom will be. To verify the accuracy of the above calculations, a comparative test between the WSADB and conventional PDC bit is performed. The results show that the WSADB has great superiorities in improving the rate of penetration (ROP), lowering the torque on bit (TOB), reducing the mechanical specific energy (MSE) and enhancing the RBE. Making full use of the advantages of higher ROP, smaller TOB and higher mechanical energy utilization of the WSADB is expected to provide a solution to the problem of low RBE of conventional PDC bit in ultra-deep wells.

[1]  M. Biot MECHANICS OF DEFORMATION AND ACOUSTIC PROPAGATION IN POROUS MEDIA , 1962 .

[2]  Babak Bahrami,et al.  Quantitative comparison of fifteen rock failure criteria constrained by polyaxial test data , 2017 .

[3]  P. Tahmasebi,et al.  A pore-scale mathematical modeling of fluid-particle interactions: Thermo-hydro-mechanical coupling , 2019, International Journal of Greenhouse Gas Control.

[4]  L. W. Ledgerwood,et al.  Mitigating Drilling Dysfunctions and Enhancing Performance with Self-Adjusting Bit Technology: Analytical and Experimental Case Studies , 2017 .

[5]  D. Gumich,et al.  Unique Approach to Bit Design Coupled with Innovative Rolling PDC Cutter Sets New Performance Benchmark Drilling Extremely Abrasive Sandstone Formations, Usinsk Region Russia , 2017 .

[6]  M. J. Fear,et al.  Quantifying Common Drilling Problems With Mechanical Specific Energy and a Bit-Specific Coefficient of Sliding Friction , 1992 .

[7]  T. M. Warren,et al.  Bottomhole stress factors affecting drilling rate at depth , 1985 .

[8]  Liexiang Han,et al.  Drilling and completion technologies for deep carbonate rocks in the Sichuan Basin: Practices and prospects , 2020 .

[9]  Seyed Ali Heydarshahy,et al.  Influences of bit profiles on possible fracture modes , 2017 .

[10]  Z. Li,et al.  An investigation of failure modes and failure criteria of rock in complex stress states , 2017 .

[11]  Wang Xiaohui,et al.  Weight-on-Bit Self-Adjusting Dual-Diameter Bit Leads a Step Change in Drilling Bit Technology , 2019 .

[12]  H. Van Heekeren,et al.  Conical Diamond Element Bit Sets New Performance Benchmarks Drilling Hard and Abrasive Formations, Offshore Netherlands , 2015 .

[13]  R. Teale The concept of specific energy in rock drilling , 1965 .

[14]  Bezalel Haimson True Triaxial Stresses and the Brittle Fracture of Rock , 2006 .

[15]  Yezid Ignacio Arevalo,et al.  Quantification of Drillstring-Integrity-Failure Risk Using Real-Time Vibration Measurements , 2012 .

[16]  J. Prévost Mechanics of continuous porous media , 1980 .

[17]  Hussain Rabia Specific Energy as a Criterion for Bit Selection , 1985 .

[18]  Waleed Agawani,et al.  Multiple Deployments of Hybrid Drill Bits with Optimized Drilling Systems Prove Enhanced Efficiency in North Kuwait Development Wells , 2017 .

[19]  Gensheng Li,et al.  Experiment on rock breaking with supercritical carbon dioxide jet , 2015 .

[20]  Malcolm Taylor,et al.  Pointing Towards Improved PDC Bit Performance: Innovative Conical Shaped Polycrystalline Diamond Element Achieves Higher ROP and Total Footage , 2013 .

[21]  M. Jabareen,et al.  Numerical modeling of rock failure under dynamic loading with polygonal elements , 2019, International Journal for Numerical and Analytical Methods in Geomechanics.

[22]  Hector Ulpiano Caicedo,et al.  Unique ROP Predictor Using Bit-specific Coefficient of Sliding Friction and Mechanical Efficiency as a Function of Confined Compressive Strength Impacts Drilling Performance , 2005 .

[23]  Lin Shi,et al.  Technologies in deep and ultra-deep well drilling: Present status, challenges and future trend in the 13th Five-Year Plan period (2016–2020) , 2017 .

[24]  J. Carcione,et al.  Computational poroelasticity — A review , 2010 .

[25]  Alexey Ruzhnikov,et al.  Drill Bit Evolution During Execution of Long-Term Offshore ERD Project , 2016 .

[26]  Wei Zhang,et al.  Equipment and technique for improving penetration rate by the transformation of drill string vibration to hydraulic pulsating jet , 2014 .

[27]  M. Kwaśniewski Recent Advances in Studies of the Strength of Rocks Under True Triaxial Compression Conditions , 2013 .

[28]  Yuanli Bai,et al.  Application of extended Mohr–Coulomb criterion to ductile fracture , 2009 .