Injecting Cooling Agents to Reduce Breakdown Pressure for Open Hole Hydraulic Fracturing Treatment

For deep and tight gas reservoirs, horizontal wells are generally drilled for maximum reservoir contact. Also, transverse hydraulic fractures are strongly desired, which suggests that the horizontal part should be drilled in the minimal horizontal stress (σhmin) direction. In this situation, formation breakdown for initiating transverse fractures can be a challenging issue for zonal isolated open hole multistage hydraulic fracturing treatment. This article presents an innovative idea on reducing breakdown pressure through cooling the borehole. It is achieved by injecting cooling agents and flowing them to the target open borehole fracturing interval. As a result, the cooling agent may lead to a temperature drop in the open borehole formation. The near borehole formation will exhibit thermal contraction, and accordingly, tensile stress increases along the borehole axial direction. Simultaneously, the thermal contraction leads to the compressive hoop stress increasing, which can inhibit the longitudinal fracture initiation. Eventually, the breakdown pressure along the borehole axis direction can be reduced and becomes easy, which boosts the chance for initiating transverse hydraulic fractures. The required axial tensile stress changes along the borehole axis, and always varies from well to well and reservoir to reservoir. For accurately estimating the required axial stress change along the borehole axis, a 3D fully coupled thermal displacement finite element model was specifically developed for facilitating the cooling agent design. Criteria to terminate the cooling process and timing of the breakdown are also offered. Examples are also provided to demonstrate the effectiveness of the method. © 2022 Aramco Services Company. All rights reserved.