High-Temperature Treated Rock Breaking Study of PDC Teeth Assisting with High Pressure CO₂ Jetting

Oil and gas resources in deep and ultra-deep strata are taking up an increasing proportion in China’s energy development. Underbalanced gas or foam drilling has a better effect, but the problem of rock breakage after high temperature damage in drilling around deep oil and gas wells is particularly prominent. In order to analyze the cutting force of high-temperature rock broken by CO₂ gas jet and PDC teeth in high-temperature well, the mechanical properties of rock after high-temperature damage were tested by uniaxial compression and Brazil splitting test. The rock test after high temperature damage was carried out on the rock breaking system of high pressure CO₂ jet and PDC gear cutting. The test results of mechanical properties show that with the increase of heating temperature, the tensile strength of sandstone decreases first and then increases sharply, and the compressive strength decreases first and then increases. The correlation analysis between cutting force and rock mechanical parameters shows that the elastic modulus of rock has strong correlation with cutting force. Combined with the experimental results of rock crushing, it is shown that the high pressure CO₂ jet can pre-strike the rock, and the jet can enhance the cuttings migration before the tooth and the cuttings discharge behind the tooth, which can significantly reduce the resistance of the cutter and reduce the cutting force required for rock crushing. Further study rocks heating temperature, nozzle diameter and jet pressure condition parameters, when the fluid pressure, nozzle diameter and jetting temperature are 20 MPa, 2 mm and 45 ℃, respectively, the jet has good impact on sandstone and rock carrying effect, and the cutting force is small, which is conductive to rock breaking. This study has important guiding significance for guiding the gas drilling technology of high temperature wells and the research and development of matching bits.