Methods for Enhancing Open-Hole Multistage Fracturing Treatment

In deep and tight reservoirs, horizontal wells are commonly drilled and fractured to increase reservoir contact. As an alternative method, open-hole multistage fracturing (MSF) employs packers to isolate multiple fracturing stages. Although some cases have shown success in post-fracturing production rates, open-hole MSF encounters notable challenges, including breakdown and stage communication. A major limitation is the difficulty in initiating transverse hydraulic fractures, even when horizontal wells are oriented in the direction of minimum horizontal stress. This study begins by examining the factors contributing to the drawbacks associated with open-hole MSF. Also we investigate the impact of perforation on fracture initiation. Subsequently we present a geomechanics workflow for selecting wells suitable for open-hole completion. More importantly, we introduce an improved fracturing process specifically designed for stimulating open-hole well. This process consists of a series of steps including: (1) creating perforation clusters along the borehole at the identified perforation locations; (2) injecting cooling agents into each isolated open-hole fracturing interval to reduce the breakdown pressure. The cooling induces thermal contraction along the open-hole section, generating tensile stress in the axial direction. As a result, the perforation cluster location becomes the weakest point along the axial direction of the open-hole and thereby facilitating transverse fracture initiation at a lower breakdown pressure. Once the cooling target is achieved, the main pump schedule proceeds with fluid injection at ambient temperature to stimulate the isolated zone. To optimize the cooling process and timing, a three-dimensional coupled thermal-displacement finite element model was also developed. Together, these enhanced approaches aim to improve the fracturing process for open-hole MSF, particularly in enabling transverse hydraulic fracture initiation. • A major limitation for open-hole MSF is the difficulty in initiating transverse hydraulic fractures, even when horizontal wells are oriented in the direction of minimum horizontal stress. The factors contributing to the drawbacks associated with open-hole MSF are investigated. • A workflow for evaluating whether a well in deep and tight reservoirs is suitable for open-hole MSF is presented. • The impact of perforation on fracture initiation is numerically investigated. • An improved fracturing process for open-hole MSF is presented, which includes adding perforation cluster, and injecting cooling agents to reduce the required breakdown pressure for transverse fracture initiation. • Criteria for timing the cooling process is given, and a couple thermal-displacement finite element model is used for cooling agent injection design.