As development has matured in Devon's Eagle Ford asset, the focus has shifted from primary development to late life optimization. The optimization options that are considered include: drilling of infill wells in the Lower Eagle Ford Member; drilling of redevelopment wells in the Upper Eagle Ford Member; and refracturing of existing wells. Remaining questions for the upside potential are: 1) What is the right development pattern for these different opportunities? 2) How would infills, redevelopment wells, and refracs interact? and 3) What is the impact of primary depletion in all these scenarios? Multi-well reservoir modeling is suited to answer these questions by considering the full lifecycle, wellbores, and the unit.
This case study focuses on reservoir modeling of two pads in DeWitt County, Texas to investigate the production dynamics of multiple refractured wells and to capture the inter-well connectivity among refractured parents and several redevelopment wells. For this purpose, a history matched simulation model with nine (9) horizontal hydraulically fractured wells was developed. Within the modeled area, five parent wells produced for about 5 years prior to four of them being refractured. The fifth parent well was only repressured prior to the completion of new redevelopment wells. Immediately after the parent wells were refractured, the four redevelopment wells were zipper fractured. Besides the stimulation information, bottomhole pressure gauge data from multiple wells was available for model calibration.
A 3D static reservoir model that integrates multi-disciplinary data from geology, petrophysics, geomechanics and engineering was utilized. A fully implicit dual-porosity reservoir simulator with special geomechanical features was used for the calibration, in which the temporal change in mean stress for each grid cell is implicitly solved together with pressure and the other flow variables using poro-elastic information. This simulator dynamically solves for fracture generation (rock deformation) and dilation of tensile fractures, as well as the subsequent fracture closure upon depletion and re-dilation of fractures as a function of net stress. The calibration effort consisted of matching the performance of all wells during the hydraulic fracturing, flow back, and depletion periods, including daily historical oil, gas, and water production rates together with the bottomhole pressure data. Predictive runs were performed to examine different development scenarios and to provide decision support for pattern optimization.
Simulations performed on the calibrated model significantly enhanced our understanding of fracture propagation in the presence of prior depletion, the dynamic nature of horizontal and vertical inter-well connectivity, and the role of refracturing in pattern development. Additionally, the study provided an assessment of refracturing operations as a mitigation strategy and an analysis of the interaction among the existing and newly created fracture networks, including how such networks are tied to the refractured and infill well performance. We demonstrate that opportunities remain in the developed sections of the Eagle Ford resource, depending on the existing wellbore geometries, prior depletion, and varying fracture geometries dictated by reservoir geomechanics and legacy completions.
