Study on the Mechanisms of In-depth Acid Job of Atomized Acids in Fractured and Vuggy Reservoirs

Fractured and vuggy reservoirs are developed with large amount of karst caves and fractures, and are of high heterogeneity. During acidizing operation, acid fluids will preferentially flow into the caves and fractures, increasing the size of the caves and affecting the extension of wormholes inside the rocks. In this paper, an acidizing technique with atomized acids that can be used to effectively develop fractured and vuggy reservoirs is presented. Atomized acids can effectively communicate the disconnected fractured and vuggy reservoir spaces, helping form good oil and gas flow channel. To clearly define the boundary of stable flow of oil and/or gas in wells acidized with atomized acids, simulation experiments with mist flow were performed and it was found that the most stable mist flow can be obtained at the following conditions:20℃, standard atmospheric pressure, gas injection rate of 60 m3/h, liquid injection rate of 20 mL/min and concentration of mist stabilizing agent (sodium dodecyl benzene sulfonate) 0.5%. Kinetic experiment of acid -rock reaction showed that at 130℃, rotational speed of 110 RPM and initial acid concentration of 15%, the reaction rate of rock-normal acid was 20.12×10-6 mol/(cm2·s), while the reaction rate of rock-atomized acid was only 1.87×10-6 mol/(cm2·s), less than the reaction rate of normal acid by an order of magnitude, indicating that atomized acids have excellent retardation performance. The corrosion rate of normal acids to N80 steel is 572.16 mm/a, while that of atomized acids to N80 steel is only 40.08 mm/a, less than one tenth of the corrosion rate of normal acids, indicating that atomized acids are quite less corrosive to tubular goods than normal acids.