Abstract
In order to improve the erosion capacity of a supercritical carbon dioxide (SC-CO2) jet, the influence of a nano-silica additive on the rock erosion characteristics was experimentally investigated. By impinging the SC-CO2 jets with nano-silica mass fractions of 0 wt % (pure SC-CO2 jet), 3 wt %, 6 wt %, 9 wt %, 12 wt %, 15 wt %, and 18 wt % on specimens of red sandstone, the erosion volumes under various operating conditions were measured and analyzed. Results show that an appropriate amount of nano-silica additive can greatly enhance the erosion ability of a SC-CO2 jet. The effect on the erosion ability largely depends on the operating conditions. For instance, when the other conditions are fixed, 6 wt %, 9 wt %, 12 wt %, and 15 wt % were the optimum mass fractions, successively, with the inlet pressure increasing from 30 MPa to 60 MPa. With the increase in ambient pressure, the optimum mass fraction is unchanged under the constant inlet pressure, while it increases under the constant pressure drop. Additionally, the optimum mass fraction decreases when the fluid temperature increases. In addition, the optimal standoff distances are about five times the nozzle diameter of the nano-silica SC-CO2 jet, and three times for the pure jet. This research provides a new method for effectively enhancing the rock erosion performance of a SC-CO2 jet.
Highlights
Supercritical carbon dioxide (SC-CO2 ) is an intermediate state between gas and liquid for carbon dioxide, when the pressure and temperature are both above the critical point (Pc = 7.38 MPa andTc = 304.13 K) [1,2]
The results showed that the rock erosion capacity of a SC-CO2 jet is stronger than that of a water jet, and that the threshold pressure is lower than that of a water jet
A large number of specimens were tested at various mass fractions of nano-silica, standoff distances, inlet pressures, ambient pressures, and fluid temperatures
Summary
Due to its unique properties and the relatively easy critical conditions which need to be obtained, SC-CO2 fluid has been widely studied and used in numerous fields [3,4,5,6]. Inside a reservoir bed, the dissolution of organic deposition by the seepage of SC-CO2 can increase the permeability of the reservoirs, and the absorbed natural gas can be displaced through competitive adsorption with SC-CO2 [15,16]. These processes help to reduce the blockage of oil and gas flow, and enhance recovery [17,18]. Using SC-CO2 as a drilling fluid will contribute to the reduction of greenhouse gas emissions and the pollution of water resources [19]
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