Research On The Bottomhole Flow Field Of Swirl Jet PDC Bit

Considering the fault of the traditional PDC bit, we import Swirl jet into PDC bit. On the basis of theoretical analysis to the stress of the rock and cuttings on the bottom hole, we simulate the flow field of swirl jet PDC bit and do experiment for testing the cuttings carrying capacity.In accord to the theoretical analysis of rock stress state in the bottom hole, cuttings actuation mechanism and the hypothesis that swirl jet make local low pressure in the bottom hole, the pressure difference between high and low pressure district can be used with the periodical actuation to bottom hole and ordinal swirl flow formed by it for decreasing rock strength, intensifying cuttings actuation, purifying and enhance drilling speed. The renormalization group RNG model is adopted, the results of the numerical simulation of swirl jet PDC bit's flow field in the bottom hole which take the affection of PDC bit crown structure and cogging into account show that straight jet cooperating with swirl jet can be more valuable in cuttings carrying than common straight jet, bottom hole swirl jet formed by heterogeneity of bottom hole flow field and bit's rotation develop the bottom hole swirl flow field which is useful for cuttings carrying and form ordinal distribution of high and low pressure district, improve stress station of rock or cuttings and enhance drilling speed. On detailed analysis, the main function of the nozzle near bit axle is carrying the cuttings away from broken surface while far from bit axle is carrying cuttings into annual, so the nozzle far from bit axle can be replaced by swirl nozzle in order to enhance the efficiency of cuttings cleaning.The result of cuttings carrying experiment of tangential injection swirl nozzle indicated that tangential injection swirl nozzle has stronger ability in cuttings carrying than common straight nozzle, with the same pump pressure and increase of jet distance, nozzle's cuttings carrying ability increase and then decrease, there exists the optimum jet distance. The optimum jet distance of this paper is 1-3 L/d. Tangential injection bore's nozzle with uneven number has stronger ability than that with even number in cuttings carrying and there exists the optimum number of tangential injection bore. Result showed that the optimum bore number is 3 and the ability of cuttings carrying is 1.5times stronger than common straight nozzle.On the basis of conclusion above, tangential injection swirl jet PDC bit and the conception of stator modulation swirl jet PDC bit have been proposed and developed. This job can be valuable for enhancing drilling speed.