Method for combined jet and mechanical drilling

Abstract

A method and apparatus for drilling combines the advantages of a high pressure fluid jet with a mechanical drill bit without the high horsepower requirements and associated equipment wear of prior jet drilling systems. A two fluid system is contemplated in which only a small portion of the drilling mud stream is clarified and pumped under high pressure to a number of jet nozzles located on the drill bit face. The high pressure fluid and concentrated drilling mud are conducted separately down the hole by a dual, concentric drill pipe. The power and equipment requirements of such a two fluid system are practical and economic because of the low flow rate and non-abrasiveness of the high pressure fluid when compared to conventional drilling fluids. The high pressure fluid combines with the concentrated drilling mud at the drill bit in order to accomplish the normal purposes of the drilling mud. The returned fluid is processed at the surface separating out solids, mud, and the mud to be clarified. This forms a closed system cycle. The fluid jets are strategically arranged with respect to the cutting teeth on the drill bit in order to minimize bit wear and to increase the drilling rate by up to five times. Two systems are disclosed. The first is a jet assisted mechanical system in which the jets are directed at the earthen formation at the cutting surface/rock interface. The second is a mechanically assisted jet system in which the jets are located between the cutting teeth.