Numerical investigation on the flow field characteristics of a new type of double-stage jetting PDC bit for deepwater shallow formations drilling

In deepwater shallow formations jet drilling, traditional cone bit has problems such as short service life, limited penetration depth, low rate of penetration (ROP) and long drilling cycle, which results in high drilling cost. In this paper, a novel efficient soil-breaking approach by forming a concave-stepped bottomhole with double-stage jet drilling in deepwater shallow formations is presented. Meanwhile, a new type of double-stage jetting polycrystalline diamond compact (PDC) bit for deepwater shallow formations drilling is introduced, and the characteristics of bottomhole flow field in deepwater shallow formations double-stage jet drilling with this bit is investigated. The results indicate that with the increase of the angle of the secondary jet flow, the decay rate of the jet flow gradually increases. Considering the stability of the surface conductor installation, the angle of the secondary jet flow should not be too large. The optimum area ratio of the primary to the secondary jetting nozzles should be about 1:1, while the area ratio being either too large or too small could go against soil-breaking to form the wellbore. The pressure energy distribution device comes into play when the ratio of pressure-energy distribution device area to inlet circulation area is less than 0.25, and it can distribute more hydraulic energy to the secondary jet flow.