Abstract

An ultra-high pressure (UHP-30,000 psi) downhole pump (DHPTM) is being developed for jet-assisted drilling. With this technology, drilling penetration rates in gas and oil wells can be increased 1.5 to 2.5 times. The prototype downhole pump was built for laboratory and field experimentation under a program with the Gas Research Institute. A second generation prototype is being supported by the U.S. Department of Energy - Morgantown.

Current development is focused on the DHP system that develops the UHP fluid stream used to assist the drill bit. The pump is located just above the drill bit. Its rated output is 22 gpm at 35,000 psi. The DHP is about the same size as and is handled like a conventional drill collar. Power to drive the DHP is taken from the conventional mud stream. Surface mud pump pressure is elevated approximately 1,500 to 2,000 psi while maintaining conventional flow rates downhole

Five field experiments were conducted with the first prototype. Observed ROP ratios varied from 1.1 to about 3.5 times conventional rates. The second prototype is currently being tested in the laboratory.

Introduction

The goal of jet-assisted drilling is to increase the rate of penetration (ROP) in deeper oil and gas wells, where the rocks become harder and more difficult to drill. Increasing the ROP can result in fewer drilling days, and therefore, less drilling cost.

In the early 1970s, the potential advantages of applying high-pressure, 15,000 psi, jet technology to increase rates of penetration (ROP) were demonstrated by Maurer et al. (1973) and by Fair (1981). They were able to demonstrate ROP enhancements with high pressure jet drilling of between 1.2 and 2.9 times conventional rates in tests conducted in Florida and Texas. Both Maurer and Fair used jet drilling bits without mechanical cutters, requiring the entire fluid stream to be pressurized. This resulted in extremely high power requirements, 2,800 and 11,200 hydraulic horsepower, reliability problems, and safety concerns.

During the late 1980s and early 1990s, FlowDril developed a system for ultra-high pressure, 34,000 psi, jet-assisted drilling. The system was described by Butler, et al (1990) and by Veenhuizen et al. (1993). About 40 gpm of the down hole mud stream was pressurized with pumps at the surface, 600 hydraulic horsepower, and conducted to the drill bit through a special dual-conduit drill string. This allowed a high-velocity jet of drilling mud at the bit to be directed at the bottom of the hole to assist the mechanical action of the bit. The system required separate high pressure surface piping, standpipe, and kelly hoses, a dual swivel, and a dual conduit kelly. Twenty-two field projects, 11 in West Texas and 11 in East Texas, totaling about 90,000 feet drilled, were conducted through Grace/FlowDril, a joint venture with Grace Drilling Company, to assess feasibility of jet-assist and to develop system reliability.

An example of the effectiveness of jet-assist is shown in Figure 1. The average, joint-by-joint ratio of the jet-assist ROP to that of the offset between 4,000 and 10,000 feet was 2.1. The data shown in Figure 2 is from a test well in East Texas in 1992 after reliability of the system had been improved.

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