Rock physics characterization of shale reservoirs: a case study

Unconventional resources are typically very complex to model, and the production from this type of reservoirs is influenced by such complexity in their microstructure. This microstructure complexity is normally reflected in their geophysical response, and makes them more difficult to interpret. Rock physics play an important role to resolve such complexity by integrating different subsurface disciplines. This study presents two rock physics workflows for a deeper understanding of shale reservoirs with regard to their matrix brittleness and kerogen content maturity. It first employs petrophysical stochastic modelling on the available conventional well logs. Then, the results of well log interpretation are used as input into a rock physics model to generate a complete set of elastic logs. Furthermore, these elastics logs are converted to Young modulus and Poisson’s ratio for highlighting brittle zones, which were confirmed by production figures. Moreover, another rock physics workflow is proposed to combine geological information and petrophysical data to characterize total organic carbon content of the shale. This rock physics model inverts velocity into its main geological components (organics, clay and clean velocities), which could furthermore be used for velocity interpretation considering geological processes. One of the velocity inverted components has a direct relationship with total organic carbon and its maturity that is normally calculated using Passey method. Passey method uses three different well logs for modelling kerogen maturity along a well path. However, implementation of this model at locations far away from the well is a big challenge for field development. The reason is the difficulty of tying Passey method results with the elastic properties and seismic cubes. The proposed geology guided rock physics model enables us to find a relationship between kerogen maturity and P-wave velocity from sonic logs. This model, furthermore, can provide a tool to somehow extend Passey method into seismic cubes.