Development of High-Pressure Abrasive-Jet Drilling
Authors: Fair John C. 
Published: December 2007

Summary
This paper summarizes efforts by Gulf Research and Development Co. (GR and DC) to complete development of a radically new high-pressure fluid jet drilling process at a full-scale drilling test facility in central Pennsylvania during 1970-73. Despite a number of significant improvements made to the system during this period, unsolved technical problems and marginal economic projections led to the decision to discontinue the project. Significant advances in system design, component performance, and unsolved problems are described.

Introduction
Drillpipe capability to transmit torque and bit capability to withstand load inherently limit energy transmitted to the cutting face during conventional rotary drilling to about 100 to 250 hp. Maurer has shown that through a combination of moderate specific energy requirement (energy required to remove a unit volume of rock) and high-power transmission capability, high-pressure jet drilling is a promising novel technique. Rock breakage by a pure fluid jet requires nozzle pressure differentials in excess of a threshold pressure that is related to the strength of the rock. Pols has shown that although soft, isotropic, permeable rock may be jet-drilled at pressure differentials of less than 7,200 psi, hard, laminated rock characteristic of shales frequently encountered in oilwell drilling may require bit pressure differentials of more than 14,500 psi. Such rock is common in deep-drilling basins where drilling rates are low and incremental footage costs are high. Pumping equipment that can operate reliably at the pressure required to drill these holes hydraulically was not believed to be available.GR and DC, as a laboratory engaged in research on novel drilling techniques during the 1960's, sought to adapt high-pressure jet cutting to deep, hard-rock drilling by augumenting the pure fluid jet through adding abrasive to the drilling fluid. Other laboratories concentrated on shallower, softer formations using hybrid fluid-jet bits with mechanical cutters to penetrate hard streaks. Following the work reported by Wyllie on the Gulf jetted-particle (or abrasive-jet) drilling system, GR and DC spent 3 1/2 years furthering the development of the abrasive-jet drilling (AJD) process. The primary purposes of this paper are to highlight the achievements of that period and to outline the status of the abrasive-jet technology at the time work on the project was halted.

Early Process Development
By the end of 1969, the potential for high drilling rates with high-pressure abrasive-jet drilling had been demonstrated in three full-scale field tests (summarized in Table 1). The abrasive used had evolved from sand (which suffered nearly total particle breakup into fines on a single pass through the bit nozzles) to steel shot that could be recycled, thus reducing abrasive makeup cost. The hardened 20-40 mesh steel shot afforded a low (1 to 2%) breakup rate for each pass through the bit and a superior penetration rate. Drilling mud had evolved from a bentonite system to a high-yield-value, high-carrying-capacity blend of attapulgite and cellulose fibers. Bit life had been extended through judicious use of various grades of tungsten carbide.Two 9-in. bit designs were available that used abrasive-jet streams from 20 0.120-in.-diameter nozzles to cut five concentric grooves and a cone in the center of the hole upon bit rotation.
JPT
P. 1379^