Modeling Case Study: Optimizing Multicluster Stimulation Uniformity in Horizontal Wells

Abstract

The performance and completion efficiency of horizontal multistage hydraulically fractured wells stimulated using the plug-and-perf technique are affected by the uniformity of the multiple perforation cluster treatment. Depending on reservoir heterogeneity, perforation design, and pumping schedule, uneven distribution of fluid and proppant among fractures connected to different perforation clusters can be defined by wellbore proppant transport hydrodynamics, fracture propagation mechanics, or a complex interplay of both. A modeling case study exploring strategies to mitigate nonuniformity of cluster stimulation is presented. Approaches to perforation and treatment optimization are chosen based on consideration of reservoir properties and their heterogeneity. A numerical model coupling a recently developed wellbore flow simulator and an advanced fracture simulator enables comprehensive simulations including both realistic fracture and wellbore modeling for complex perforation designs, treatment schedules, and distributions of reservoir inhomogeneities. The wellbore simulator considers proppant transport and settling, fluid rheology, perforation erosion, rate- and concentration-dependent pressure drop, and variable efficiency of proppant transport to perforations. The fracture simulator models fracture growth, fluid flow, proppant transport inside fractures, and interaction between fracture branches due to stress shadow effect. The interaction between hydraulic and pre-existing natural fractures plays a critical role during fracturing treatments in formations with pre-existing discrete fracture network (DFN). The model considers the effect of formation heterogeneity on fracture propagation, arrest of hydraulic fractures, crossing and opening of natural fractures depending on their properties, fluid viscosity, rate, and stress conditions. Several approaches for optimization of proppant distribution are suggested for cases showing nonperfect proppant transport efficiency caused by high proppant grain inertia. Tapered perforation designs enable achieving more even proppant distribution. However, perforation distribution among clusters providing best stimulation uniformity is sensitive to uncertainties in characterization and heterogeneity of reservoir and discrete fracture network properties. A combination of tapered perforation design and the suppression of inertial effects by increasing carrier fluid viscosity is more robust with respect to reservoir properties variation.