This paper presents a calibration and optimization workflow using a fully coupled hydraulic fracturing, reservoir, and geomechanics simulator, as applied to the HFTS-2 dataset in the Delaware Basin, Texas, USA. Modeling began with building a geomechanical stress profile using the viscoelastic stress relaxation (VSR) method. The model was then calibrated to key observations from the field diagnostic data, which included: horizontal and vertical well DAS/DTS/DSS fiber, downhole microseismic arrays, pressure gauges, core-through data, image logs, DFITs, proppant-in-cuttings analysis, interference tests, and production data. Finally, the calibrated model was used to perform an economic optimization of design parameters by running hundreds of variations and comparing their performance. Model calibration required adjustment of global parameters for fracture toughness, leakoff, and viscous pressure drop, as well as fracture toughness in a few specific layers. Production and depletion observations were matched by adjusting a global permeability multiplier, relative permeability curves, and pressure-dependent permeability reduction with depletion. Only the toe sections of the child well(s) were overlapping with the depleted zone from parent wells. This allowed the model to be calibrated to data from both the un-depleted and depleted parts of the well, where the latter was observed to have more lateral asymmetry.
The ‘best case’ simulation from the optimization algorithm has a 60% increase in NPV/section over the base case design. Sensitivity analysis on economic performance found that spacing and landing zone are the primary drivers of performance due to their impact on effective drainage area. Proppant loading and cluster spacing were also performance drivers due to their contribution to fracture conductivity and effective fracture length.
The comprehensive dataset that was used for model calibration enables an extremely well-constrained model, improving confidence in the model's predictions. The applied workflow demonstrates how physical insights and understanding of fundamental performance mechanisms allow for the prescriptive design of horizontal fractured wells in shale basins.