The development of unconventional resources has increasingly focused in liquid rich systems in the recent years in the USA, due to relatively low natural gas prices and conversely high oil prices. In order to maximize production and optimize the development of these resource plays, adequate modeling of wells and reservoir performance is required. Reservoir simulation has been recognized as one of the most acceptable tools to model the performance of liquid rich shale (LRS) systems. Analytical solutions (DCA, RTA, PTA) exhibit several limitations to properly model the effects of multiphase flow, stress and pressure dependent permeability, condensate banking, flow through hydraulic fractures and stimulated rock volume (SRV) region, etc. on the reservoir performance of LRS plays.
Single well modeling has been extensively used to model well and reservoir performance from shale plays, but multi-well or sector modeling is not frequently performed mainly for two reasons: 1) The requirements to capture the behavior of multiple horizontal wells with multiple hydraulic fractures could be computationally prohibitive and 2) The wells in extremely low permeability formations would have minimal interaction. Although the first reason could be a legitimate limitation depending on the objectives of the reservoir project, the second one is arguable. Depending on the spacing and the volume of the fracturing treatments, in many cases, production data collected from shale plays have shown that horizontal wells may interfere with each other during production. Therefore, in projects where the main objective is well spacing or completion optimization (among other important objectives) a comprehensive multi-well reservoir simulation study is required.
This paper discusses several aspects that highly impact the reservoir simulation workflow for LRS plays: Geomodeling (seismic, geology and petrophysics), gridding (tartan grids, Cartesian grids, and unstructured gridding), PVT, flow models (dual/single porosity models), hydraulic fracture modeling, microseismic and SRV estimations, among others. The study suggest that in multi-well reservoir simulation of LRS plays, optimum grid design, proper capture of SRV and natural fractures corridors, and adequate modeling of PVT properties are the most critical factors to accurately optimize wells and completions spacing. Finally, a reservoir simulation workflow is proposed to properly address the critical factors. Field examples from the Eagle Ford and another emerging shale play are presented to support the proposed workflow.