(333c) Understanding the Impact of Formation Properties on Stress Shadow in Multistage Hydraulic Fracturing through Modeling and Simulation

Multistage hydraulic fracturing (MSHF) is a standard technique used to increase reservoir contact with a horizontal wellbore to produce hydrocarbons from tight, unconventional oil plays. A typical Bakken completion consists of 50 stages, with three to four perforation clusters per stage. An induced fracture will propagate from an initiation point, often intersecting natural fractures or other plains of weakness, enhancing connectivity between the wellbore and the reservoir. The geometry and propagation of hydraulic fractures within a fracture stage are influenced by the distribution of reservoir properties (e.g., Young’s modulus and Poisson’s ratio). Microfractures around the hydraulic fracture (macrofracture) are generated by fluid leak-off during stimulation. The microfractures improve overall fracture conductivity and extend the stimulated reservoir volume (SRV) that can result in short- and long-term increases in well productivity and hydrocarbon recovery factor.

The magnitude and orientation of principal stresses affect the geometry of induced fractures. A hydraulic fracture will preferentially propagate perpendicular to the minimum principal stress. As closely spaced hydraulic fractures develop and interact with each other, the stress in the zone being stimulated accumulates, resulting in a stress shadow. The stress shadow modifies the contrast between principal horizontal stresses (S_{H_max} – S_{H_min}), influencing fracture development (i.e., orientation and geometry). The impact of stress shadows can be managed by controlling the spacing of stimulations and taking into account the reservoir properties in the MSHF design.

To investigate the effect of reservoir properties and stress contrast on stress shadow, a three-stage fracture model was generated in a three-dimensional lattice-based simulator. The models were built using Bakken rock mechanical properties and stress tensors. The three-stage fracture models were simulated in two phases to understand the effect of each parameter. Results suggest that more effective MSHF can be designed by managing fracture spacing. The simulation implies that fracture spacing is affected by reservoir properties, principal stresses, and fracture geometry. Principal stresses and Young’s modulus play a more important role in fracture propagation and stress shadow development than Poisson’s ratio.