Foam stability and acidizing effect evaluation of a foam acid fluid system for low-temperature dolomite geothermal reservoir stimulation

Abstract

Acidizing improves reservoir productivity, and foam acid fluid systems achieve both effective acidizing and reservoir protection compared to conventionally utilized acid fluids. Nevertheless, the current application of foam acid fluids is restricted to oil-gas reservoir stimulation, owing to the differences in development conditions between oil-gas and geothermal reservoirs. The transformative application of foam acid fluids from oil-gas to geothermal reservoirs can address the problems induced by conventional acid fluids in geothermal reservoirs, such as limited effective acidizing distance and difficulties in flowing back residual fluids. Here, a foam acid fluid system with typical foaming agents, including sodium dodecyl sulfate (SDS), cocoamidopropyl betaine (CAPB), dodecyl trimethyl ammonium bromide (DTAB) and decaethylene glycol monododecyl ether (DGME), with various foam stabilizer xanthan (XC) contents (0.3 %–1.2 %) is proposed. Its feasibility in low-temperature (25 °C−90 °C) geothermal reservoir stimulation is verified through foam stability and acidizing effects, containing dissolution and corrosion inhibition performances. The results shows that the foam acid fluids with DTAB and DGME at 1.2 % XC have a required foam stability. A network micro-structure of foam stabilizers, the stronger intermolecular forces in the foaming system, and the chemical reaction stability of foaming agents, mutually contribute to the foam stability. Compared to non-foam acid fluids, foam acid fluids significantly retards acid-rock reaction, with a more uniform dissolution of the cuttings microscopically. The existence of bromide ion (Br⁻) in DTAB enhances the corrosion of N80 steel, which is above an accepted corrosion speed. This study highlights the great application potential of foam acid fluid system in an efficient stimulation of low-temperature dolomite geothermal reservoirs.