Local Stress Reconstruction of Multi-radial Wells for Enhancing Stimulated Height of Shale Oil Reservoir

The technique combined radial well and hydraulic fracturing is an efficient and innovative method to enhance stimulated height of shale oil reservoir. In this paper, a 3D double-layer radial well-fracturing fracture initiation model considering fluid-mechanics coupling is established and the property of shale is characterized by considering the transverse isotropy of elastic modulus, Poisson’s ratio and shear modulus simultaneously. The influences of radial well diameter, length, spacing, and in-situ stress on the fracture initiation characteristics induced by vertical stress interference around the radial wells are investigated by superimposing the stress fields generated by the main well and radial wells. The results show that the induced stress field is gradually decreasing from the radial well to the surrounding reservoir. Increasing the diameter and length of radial well and decreasing the horizontal stress difference can increase the influence of induced stress field and improve the ability to guide the vertical-fracture propagation. When the radial well diameter increases from 20 to 100 mm, the interwell induced stress decreases by 5.66%. When the radial well length increases from 1 to 40 m, the interwell induced stress decreases by 3.72%. When the horizontal stress difference decreases from 15 to 1 MPa, the interwell induced stress decreases by 1.32%. In addition, the radial well spacing is an important factor affecting the induced stress field. With the radial well spacing decreasing from 3 m to 0.5 m, the induced stress field between radial wells increases obviously. The local compressive stress of the reservoir is reduced, and the vertical-fracture connectivity is improved. The research results can provide a basis for the fracture-communication mechanism of multi-radial wells fracturing in shale oil reservoirs.