Influences of ambient pressure and nozzle-to-target distance on SC-CO2 jet impingement and perforation

• Non-submerged SC-CO2 jet changes to submerged one as ambient pressure increases.
• SC-CO2 has longer and varying jet potential core than water due to compressibility.
• Fluid properties leads to particular variations of jet impingement and perforation.
• SC-CO2 is more suitable in slim-hole operations than water- and oil-based fluids.

It is reported that supercritical carbon dioxide (SC-CO2) jet can efficiently erode rocks at a comparably low threshold pressure with high penetration rate. However, the influences of bottom-hole pressure and borehole irregularities on SC-CO2 jet cutting efficiency have not been studied. Therefore, in this research, comprehensive methods of numerical simulations and lab experiments were carried out to investigate the influences of the ambient pressure and the nozzle-to-target distance on the jet impinging pressure and perforation performance. Results show that, both the effective jet impinging pressure and the eroded depth of perforation hole notably decrease with the increase of the ambient pressure, when jet inlet pressure is constant. When the pressure difference between inlet pressure and ambient pressure is kept constant, the effective impinging pressure hardly changes with ambient pressure, but eroded depth increases at first and then decreases, bounded by the critical pressure of CO2. As the nozzle-to-target distance extends, both the depth and volume of the perforation hole decrease, and diameter of the perforation hole increases at first and then decreases. Under the research condition of certain pressure and temperature, a distance of 8 times the nozzle diameter is the critical distance that clarifies the different effect of nozzle-to-target distance on the hole diameter. Different features between using SC-CO2 jet and water jet, including the optimal distance for rock-erosion efficiency, are attributed to the difference in fluid properties. Further simulation results show that, unlike water, SC-CO2 fluid is compressible and it leads to specific variations of jet structure, namely the increase of length of SC-CO2 jet potential core, and flow type from non-submerged jet to submerged jet. As a consequence, under the simulated bottom-hole conditions, SC-CO2 jet is proven to be able to acquire high rock-erosion efficiency and the jet-assisted drilling rate at a larger application ranges. This research can promote the future application of SC-CO2 jets.

The plot sees notable increase of axial velocity of SC-CO2 jet potential core (Vc), and what's more important, the increase of length of the jet potential core (lc). It increases from 48.73 mm to 61.42 mm (approximately 8–10 times Φn), or by approximately 26.04%, while that of water jet hardly change and is kept constant at 39.93 mm (approximately 6.5 times Φn) under the same condition. It indicates the wider application range of SC-CO2 jet, and also explains why SC-CO2 jet has specific impinging pressure and rock-erosion features. What's more, under the same bottom-hole conditions, the operation performance using SC-CO2 is proven to be better than that of water jet.Figure optionsDownload high-quality image (391 K)Download as PowerPoint slide