Calcium Precipitates as Novel Agents for Controlling Steam Channeling in Steam Injection Processes for Heavy Oil Recovery

Unconventional heavy oil reservoirs are particularly susceptible to steam breakthrough, which significantly reduces crude oil production. Profile control is a crucial strategy used for stabilizing oil production and minimizing production costs in these reservoirs. Conventional plugging agent systems used in the thermal recovery of heavy oil currently fail to meet the high-temperature, high-strength, and deep profile control requirements of this process. Precipitation-type calcium salt blocking agents demonstrate long-term stability at 300 °C and concentrations up to 250,000 mg/L, making them highly effective for profile control and channeling blockage during the steam injection stages of heavy oil recovery. This study proposes two types of precipitation-type calcium salt blocking agents: CaSO₄ and CaCO₃ crystals. The precipitation behavior of these agents was investigated, and their dynamic growth patterns were examined. The calcium sulfate blocking agent exhibits a slower crystal precipitation rate, allowing for a single-solution injection, while the calcium carbonate blocking agent precipitates rapidly, requiring a dual-solution injection. Both systems incorporate scale inhibitors to delay the growth of calcium salt crystals, which aids in deep profile control. Through microscopic visualization experiments, the micro-blocking characteristics of the calcium salt blocking agent systems within pores were compared, elucidating the blocking positions of the precipitated calcium salts under porous conditions. Calcium sulfate crystals preferentially precipitate in and block larger pore channels, whereas calcium carbonate crystals are more evenly distributed throughout the pore channels, reducing the reservoir’s heterogeneity. The final single-core displacement experiment demonstrated the sealing properties of the precipitation-type calcium salt blocking agent systems. The developed precipitation-type calcium salt blocking agent systems exhibit excellent profile control performance.