Characterization of organic-rich shales for petroleum exploration & exploitation: A review-Part 3: Applied geomechanics, petrophysics and reservoir modeling

Modeling geomechanical properties of shales to make sense of their complex properties is at the forefront of petroleum exploration and exploitation application and has received much research attention in recent years. A shale’s key geomechanical properties help to identify its “fracibility” its fluid flow patterns and rates, and its in-place petroleum resources and potential commercial reserves. The models and the information they provide, in turn, enable engineers to design drilling patterns, fracture-stimulation programs and materials selection that will avoid formation damage and optimize recovery of petroleum. A wide-range of tools, technologies, experiments and mathematical techniques are deployed to achieve this. Characterizing the interconnected fracture, permeability and porosity network is an essential step in understanding a shales highly-anisotropic features on multiple scales (nano to macro). Well-log data, and its petrophysical interpretation to calibrate many geomechanical metrics to those measured in rock samples by laboratory techniques plays a key role in providing affordable tools that can be deployed cost-effectively in multiple well bores. Likewise, microseismic data helps to match fracture density and propagation observed on a reservoir scale with predictions from simulations and laboratory tests conducted on idealised/simplified discrete fracture network models. Shales complex wettability, adsorption and water imbibition characteristics have a significant influence on potential formation damage during stimulation and the short-term and long-term flow of petroleum achievable. Many gas flow mechanisms and models are proposed taking into account the multiple flow mechanisms involved (e.g., desorption, diffusion, slippage and viscous flow operating at multiple porosity levels from nano- to macro-scales). Fitting historical production data and well decline curves to model predictions helps to verify whether model’s geomechanical assumptions are realistic or not. This review discusses the techniques applied and the models developed that are relevant to applied geomechanics, highlighting examples of their application and the numerous outstanding questions associated with them.