Experimental investigation on the rock erosion characteristics of a self-excited oscillation pulsed supercritical CO2 jet

Abstract

Supercritical CO2 (SC-CO2) jet is now widely considered to have great potential for application in oil-gas exploration and development. In order to further improve the performance of SC-CO2 jet, the rock erosion characteristics of a self-excited oscillation pulsed SC-CO2 jet (SOPSJ) were preliminarily analyzed and then experimentally studied as a pioneering effort. A Helmholtz oscillation nozzle was employed to generate a SOPSJ. Numerous rock erosion tests were conducted. Rock erosion area and depth, erosion intensity evaluated by mass loss, and erosion rate were applied to characterize the erosion performance of a SOPSJ. Results show that unlike the continuous SC-CO2 jets, the erosion areas caused by the SOPSJs are almost unchanged at first and then decrease slowly with the growing standoff distance, while the erosion depths increase first and then decrease. The erosion pits caused by the SOPSJs are relatively large, shallow, and irregular, especially at the initial several standoff distances. Moreover, the SOPSJs can cause larger mass losses than the continuous jets, but this only happens at the initial several standoff distances. The SOPSJs generated with the use of the optimum chamber lengths can maximally enhance the mass loss by about 32.3%, 27.7%, 21.5%, and 17.3% at inlet pressures of 25, 30, 35, and 40 MPa, respectively. In addition, for all the jets, the erosion rates always remain the tendency to decrease with the increase of erosion time. Whereas, the specimens can be eroded by the SOPSJs at a higher rate than the continuous jets, which is independent of the inlet pressure.