The purpose of this work is to build a real three-dimensional (3D) method for optimizing the design of stage intervals in multistage hydraulic fracturing and design of horizontal well spacing in unconventional oil and gas resources. The method proposed in this paper uses continuum damage mechanics as its basis for modeling fractures and their propagation under stimulation injection. The volumetric density of cracks created by injection fluid is represented by a set of two scalar-damage variables. This method can provide a solution for fracture propagation in two horizontal directions. This solution is used for the optimized design of stage intervals for multistage hydraulic fracturing and for the optimized design for well spacing in parallel horizontal wells. The determination of optimized stage intervals considers the overlapping effect of two nearby stimulation stages. A validation example of a design for the hydraulic fracturing of a set of parallel horizontal wells in a tight-sand oil formation is presented. A 3D numerical model was built for this purpose. A numerical solution for the distribution of continuum damage variables under stimulation-injection loads is obtained with a poro-elastoplastic damage model by using the finite element method. The effective fracture length with the critical value of synthetic damage variable (DV) is determined. The optimized stage interval and well spacing are determined, respectively, with reference to numerical results of continuum damage distribution generated by stimulation. The critical value for the synthetic DV is the value of the DV that can represent the opening of an effective fracture. The distribution of synthetic DVs generated by stimulation injection was calculated and analyzed. The stage interval along the well trajectory and the well spacing are determined by using the numerical results of continuum damage distribution. This method can provide a fracture propagation solution in three directions of a 3D volume, which creates a real 3D method for fracturing analysis.

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