Study On Rock Breaking Effect Of Cutting Teeth Of PDC Drill Bit In High Temperature And High Pressure Complex Strata

The rapid growth of China’s economy has brought forth significant energy shortages and environmental concerns resulting from the extensive use of fossil fuels.As a result,there is an urgent need to develop efficient and eco-friendly renewable energy alternatives.Due to its large reserves,wide distribution and high stability,geothermal energy is gradually becoming one of the best alternatives to existing non-renewable resources.Nevertheless,the commercialization of geothermal energy is challenged by the complexities of its mining process,with geothermal drilling being the primary hurdle.At present,the PDC bit is the principal tool used for geothermal drilling.However,the PDC bit’s rock-breaking ability is severely impaired by variations in the physical and mechanical properties of rocks under high temperature and pressure conditions,leading to increased development costs due to frequent stoppages and starts.To this end,this paper investigates the crushing effect of granite with changes in temperature and lamina angle from multiple perspectives,using uniaxial compression,Brazilian splitting,three-point bending and MCT scanning as the most common granite in dry thermal rocks;a simulation model is established based on the mechanical parameters of the rock body obtained from the test,and further investigates the effect of different The simulation model was established based on the mechanical parameters of the rock body,and the effect of different temperatures and different cutting tooth parameters on the effect of rock cutting and breaking was further investigated.The simulation model was established based on the mechanical parameters of the rock body,and the effect of different temperature and cutting tooth parameters on the cutting effect was further investigated.The study provides a theoretical framework for designing drilling tools in complex rock formations.The primary research work of this study includes:(1)The rock-breaking mechanism of the PDC bit and the force on the cutting teeth were analyzed,and the key factors affecting the rock-breaking effect of the cutting teeth were clarified to include two aspects:(1)cutting tooth inclination,rotational speed and cutting depth;(2)rock lamina angle,temperature and mechanical property parameters.(2)Carrying out a series of tests on water-cooled granite at varying temperatures to examine the effect of temperature on the physical and mechanical properties of the rock.The study results indicate that with increasing temperature,the compressive strength,elastic modulus,and Poisson’s ratio of granite decrease,while the tensile strength and type I fracture toughness first increase and then decline,peaking at 300°C.Combined with the evolution law of its pore structure,granite is affected by high temperature in two stages: relative low temperature stage(25℃-300℃)and relative high temperature stage(300℃-600℃).The crushing characteristics of granite after different tests were analyzed,and the influence of lamina structure on granite crushing was clarified.(3)According to the results of physical and mechanical properties of granite,the rock models were established by taking the intermediate temperatures of 200℃and 500℃ in two stages.By simulating the rock-breaking effect of different PDC drill cutting tooth parameters on these two rock models,the optimal parameters of PDC drill cutting tooth in low temperature stage and high temperature stage were given.When the temperature is lower than 300℃,the optimal parameters of cutting tooth are 15° of cutting tooth inclination,2mm of cutting depth and 80 rpm of cutting tooth speed;when the temperature is higher than 300℃,the optimal parameters of cutting tooth are 20° of cutting tooth inclination,2mm of cutting depth and 90 rpm of cutting tooth speed;the influence of temperature and lamina structure on the breaking effect of cutting tooth is analyzed,and the optimal cutting temperature is 200℃;the laminate structure will reduce the cutting force by 5.58%,but the cutting force fluctuates greatly,and will cause a large amount of rock debris to accumulate in the cutting tooth attachment,and have a certain impact on the cutting effect,which needs to be solved by taking certain additional vibration measures.