Research On Plow-crushing PDC Bit Adapted To Hard Formation

Block71of Yemen is the key exploration block of Sinopec in the Middle East and hasgood prospects of oil and gas exploration. In order to solve the problem of low ROP and shortbit life in granite-metamorphic formation and speed up the progress of E&D, newhigh-efficient bit should be studied urgently. The drilling properties of plow-crushing PDC bit,the rock-breaking mechanism and law of conical PDC cutter were deeply studied based onbench test, numerical simulation, and theoretical analysis.(1) Two plow-crushing PDC bitswith different cutter shapes, one conventional PDC bit and two hybrid PDC bits weredesigned.(2) Using the five PDC bits, bench tests were carried on in granite, hard limestoneand hard sandstone. The test results show that the plow-crushing PDC bit has the ability ofdrilling hard rock; the ROP increases with the increase of WOB in power function orquadratic function; under the same WOB, the higher RPM, the greater ROP is; goodadaptability in the hard granite and limestone, while poor in hard sandstone; the rock-breakingefficiency of the plow-crushing bit with sharp cutters is higher than that with blunt cutters; theROP of plow-crushing PDC bit is lower than that of hybrid PDC bit and conventional PDC bitunder the same WOB; when the WOB is below a certain value, the ROP of hybrid PDC bitwith sharp cutters is lower than that of conventional PDC bit, and it increases rapidly whilethe WOB is greater than that value.(3) By choosing Drucker-Prager criterion as the rockconstitutive model, equivalent plastic strain as the failure criterion, the FEA model ofrock-cutting by conical PDC cutter was established, which was based on ABAQUS. Throughnumerical simulation and theoretical analysis, the rock-breaking mechanism of conical PDCcutter was elaborated: shear failure in tangential and tensile fracture failure in lateral direction,adjacent effect was also elaborated.(4) The influence laws between rock-breakingefficiency and cutting depth as well as cutting angle were simulated, and the optimal cuttingangle20°was selected.