Analysis of the Influence of Deep/Ultra-Deep Rock Mechanical Properties Difference on Rock Breaking Efficiency of PDC Bit and Research on Cutter Shape Optimization-Taking Shunbei Oilfield as an Example

ABSTRACT Polycrystalline diamond compact (PDC) is widely used in petroleum engineering drilling due to its strong wear resistance, fast penetration rate and high bit footage. But with the increase of formation depth, the formation rocks become dense, high strength and difficult to be destroyed under the action of geostress, which makes the drilling speed in deep/ultra-deep layers slow. In this paper, the characteristic law of rock strength characteristics changing with well depth is analyzed, and the numerical simulation model of single cutter rock breaking based on the Cohesive element is established. According to the numerical simulation results and the change of confining pressure with depth in Shunbei Oilfield, the suitable depth range of each cutters is recommended by layers. The results show that the rock strength characteristics gradually increase with the depth, and the impact on the rock breaking of the cutting teeth is mainly the increase of the weight on bit and the cutting force. By analyzing the numerical simulation results, the circular cutter is suitable for shallow formation, the curved cutter is suitable for medium and deep well section, and the triangular cutter is suitable for ultra deep formation. INTRODUCTION Oil and natural gas are the main raw materials for obtaining energy in the world today. With the improvement of the development level of oil and natural gas, the depth of recoverable oil reservoirs is getting deeper and deeper, and the depth and number of deep/ultra-deep wells are also increasing. (Wang HG, Huang HC, Bi WX, et al. 2021). For these deep/ultra-deep wells, the traditional drilling methods cannot effectively drill, and it is difficult to meet the needs of rapid deployment of well patterns in the oilfield. (Tian S, Huang Z, Niu J, et al. 2009). Therefore, it is quite necessary to carry out the research on rock breaking law of PDC cutters for deep/ultra-deep layers.