Ultrahigh-Pressure-Jet-Assisted Drilling Technique: Theory and Experiment

Abstract

Summary The ultrahigh-pressure-jet-assisted drilling technique can increase the rate of penetration (ROP) greatly. A downhole boost compressor and an ultrahigh-pressure polycrystalline-diamond-compact (PDC) bit with dual-flow channels are the core techniques of ultrahigh-pressure-jet-assisted drilling. During recent years, the China University of Petroleum, Beijing (CUPB), has focused on theoretical and experimental research--for example, the hydraulic structure and performance of downhole boost compressors, boosting theory, reversing control, rock-breaking mechanics under ultrahigh-pressure-jet conditions, and structural-design theory of ultrahigh-pressure PDC bits with dual-flow channels. On the basis of theoretical research, CUPB has designed and manufactured two generations of downhole-boost-compressor prototypes. At the same time, five oilfield-test experiments have been performed in the SINOPEC ZhongYuan oil field and CNPC TuHa oil field, China. As these experimental results showed, a downhole boost compressor and an ultrahigh-pressure PDC bit with dual-flow channels can increase ROP by over 50% under the five different sets of experimental conditions, and can meet the field-operation requirement. This research, outlined in the paper, played a leading role in the development of the ultrahigh-pressure-jet-assisted drilling technique. As one of the main techniques to increase ROP, ultrahigh-pressure-jet-assisted drilling is always a popular research project, and since the 1960s, research institutes worldwide have made significant progress (Veenhuizen et al. 1996, 1997a, 1997b; Butler et al. 1990). To date, the ultrahigh-pressure-jet-assisted drilling technique has gone through three main stages of development: the ground equipment to boost the pressure (1960s-70s), the ultrahigh-pressure-drill system with dual-flow paths (1980s-90s) (Maurer 1980), and the downhole boost compressor (1990s-present) (Wang 2005, 2008). For downhole boost compressors, there are three different structures: turboboost, screw boost, and piston boost. Compared with the first two structures, piston-boost compressors have a much simpler structure, shorter total length, and better application for deviated wells and horizontal wells (Liu 1993; Meng 1997). CUPB has long been focused on research on a downhole boost compressor that is based on piston-boost structures. The main research results are as follows: boosting theory, downhole-boost-compressor hydraulic structural-design theory, downhole-boost-compressor material research, ultrahigh-pressure-jet hydraulic-character research, structural design of ultrahigh-pressure PDC bit with dual flow channel, and rock-breaking mechanisms of ultrahigh-pressure PDC bits with dual-flow channels. In 2005, CUPB successfully manufactured the first generation of prototypes of downhole boost compressors and ultrahigh-pressure PDC bits with dual-flow channels, and updated to the second generation in 2008. In this process, more than 10 repetitions of laboratory and field experiments were completed, and these results can play a positive role in the development of ultrahigh-pressure-jet-assisted drilling techniques.