Method to Create Multiple Collocated Hydraulic Fractures Using a Temporary Localized Change in Stress Anisotropy Produced During an Initial Stimulation Treatment

Abstract

Abstract During a hydraulic fracturing stimulation treatment, transient geomechanics forces are exerted on the formation which modify the stress landscape near the wellbore and fracture planes. In regions where the horizontal stress anisotropy is less than 25%, there is a possibility for a temporary reversal in the minimum stress direction. During this brief window, a secondary hydraulic fracture can be created in a completely different direction, thus providing direct connectivity to previously unattainable locations in the formation. This paper presents a computational validation of the multioriented hydraulic fracturing (MOHF) process. As traditional hydraulic fracture simulations are derived using static formation properties and steady-state assumptions of the formation behavior, a unique transient 3D computational geomechanic fracture simulator was developed to perform this study. The new model incorporates cohesive zone elements to represent the fracture plane, and captures the dynamics of the fracture initiation and propagation, as well as the transient stress modification in the formation. A realistic 3D fracture transient behavior is accounted for by the inclusion of multiple rock layers in the model, which are connected through energy absorbing frictional elements. The simulations provide time sensitive operational recommendations for performing the MOHF stimulation to achieve maximum production increase from the well. Time lapse stress fields show vivid windows of opportunity where new fractures can be influenced to extend in alternate directions, hence offering formation drainage not attainable using conventional stimulation approaches. Production levels of twice to five times were predicted using reliable production simulators. This new stimulation method enhances the state-of-the-art in hydraulic fracturing by requiring an understanding of the transient geomechanic response in the treatment area. As a time dependent method, this approach opens a new window of opportunity—both in conventional and unconventional plays—by providing connectivity to previously unattainable locations in the formation. Unfortunately, it also brings new complications. Industry standard fracture simulation technology becomes incomplete, as most models neglect the transient response of the system. Additionally, the availability of data related to the dynamic behavior of rocks is limited. The dynamic compression of the rock, slip characteristics between rock layers, and the amount of energy stored within slip planes—all recorded as a function of time—are particularly important when considering an MOHF process. Additional testing must be performed to obtain these data.