Elastic Property Estimation in Digital Multiporosity/Multipermeability Cores

Abstract

A rock-physics-based evaluation of elastic properties is examined in a coal core, using a three-dimensional (3D) reservoir simulator with an embedded petro-elastic model (PEM) to facilitate the evaluation of fracture productivity mechanisms. The analysis expedites what-if scenario evaluation at reduced costs compared to laboratory experimentation. The flow rates and capillary pressure are incorporated into a simulated coreflood to assess the effect of production on elastic properties at the core scale. A simulated coreflood is performed using an automated steady-state fractional flow process for mixed rock-type systems, which was developed as part of a process automation controller for a reservoir simulator. The process automation promotes adherence to established laboratory-based coreflooding procedures while optimizing for work process efficiency. Typical steady-state modeling processes are characterized as occurring in the capillary limit (CL) or viscous limit (VL) conditions, which are differentiated by flow velocity and capillary equilibration. The elastic properties are calculated by the reservoir simulator during the simulation, based on two available petro-elastic modeling methods—one semi-empirical and the other explicit, based on simulator parameters. The impact of flow rate, capillary pressure, and production on the elastic properties of a coal core are evaluated by simulated primary imbibition coreflooding with application to coal bed methane (CBM) production. The elastic properties are analyzed directly while also considering a dimensionless elastic property formulation. This dimensionless determination amplifies changes in elastic properties that might not otherwise be observed in the results directly; additionally, it combines spatial and temporal changes into an amalgamated variable. In addition to the spatio-temporal characterization of the dimensionless solution, results also show that it is consistent with the pressure solution over a given interval of simulated time. Differences in simulated coreflooding results are observed, which are driven by disparate flow regimes and applied capillary pressure. The differences are attributed to the CL condition imbibition coreflooding results showing decreased affinity to the wetting phase compared to VL-based simulation results. The flow component of the digital coreflooding results is considered valuable to overall asset productivity management. The evolution of simulated elastic properties in the digital core similarly shows that changes in saturated rock properties develop with specific flow conditions and highlights potential uses for core scale analysis in fracture productivity assessment.