This paper introduces a new carbon dioxide (CO2) -hybrid fracturing-fluid design that intends to improve production from ultratight reservoirs and reduces freshwater usage. The authors present simulation work that demonstrates how CO2, with its low viscosity, can extend the bottomhole treating pressure deeper into the reservoir and generate a larger producible surface area. They also present experimental evidence that CO2 leaves behind higher unpropped-fracture conductivities than slickwater (hereafter designated as FR water).
Introduction
The theory of improved recovery with the CO2-hybrid fracturing design is predicated on the assumption that current stimulation treatments with water-based fluids understimulate the reservoir by leaving behind damaged (conductivity-inhibited) stimulated regions deeper in the reservoir. Conversely, O2 can improve drainage and recovery from these unpropped regions by (1) extending the bottomhole treating pressure deeper into the reservoir, (2) improving the stimulated fracture coverage by increasing both the number of stimulated fractures and their density (number of fractures per unit of volume), and (3) improving the conductivity of the stimulated unpropped channels.
The ambition is that CO2, with its subwater viscosity, can stimulate even more reservoir surface area per unit volume pumped (Fig.
