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Technical Committee on Petroleum Geology

MERID - Microstructural influence on reservoir integrity under variable hydromechanical pressure conditions

In the research project, the anisotropy of Rotliegend reservoir rocks on the grain scale was recorded and its influence on the hydrodynamics on the reservoir scale was determined. This involved quantifying the permeability anisotropies in the experiment and in the natural analog, and determining the representative volume of anisotropy in the reservoir rock. Finally, the hydrodynamics of multiphase transport during pressure change in the reservoir was modeled at the grain scale considering the wetting properties as digital rocks, and the influence of microstructures on reservoir integrity was evaluated. A better understanding of the geological control factors on the poroelastic rock mechanics and interaction with fluid transport could be experimentally validated and computed by flow simulations at the micro and reservoir scales.
The pressure-dependent change in permeability correlates with the rock composition on the microscale. Fine-grained sandstones with well-developed clay cutans and low initial permeability are more pressure-sensitive than medium-grained sandstones with poorly developed clay cutans and medium initial permeability. Medium-grained sandstones with well-developed clay cutans and high initial permeabilities show the lowest pressure sensitivity. With these results, pressure sensitivity could be coupled with rock composition for the first time.
Furthermore, geomechanical properties (unconfined strength, modulus of elasticity, elongation at fracture) could be correlated with petrographic properties. The contact length of detrital grains and diagenetic cements correlates with these properties. A rock strength parameter is derived from the ratio of porosity to effective contact length, which can be used to estimate geomechanical parameters.
The coupling of fluid flow simulations and geomechanical simulations has been successfully performed on different platforms. While classical fluid flow simulations do not take into account effects of compaction under variable pressure conditions, these effects can now be represented by coupled simulations. For this purpose, a coupling software was developed, which exchanges the data sets between different simulation programs and coordinates their coupling. Geometrical problems in data transfer between unstructured grids and structured grids were solved. For this purpose, a system was developed which can exchange the data independently of the present shape on the basis of the mathematical formulation of a convex hull.
Advances in the field of flow simulation relate to the reduction of unphysical fluid velocity fields at the interface between immiscible fluids in the Lattice-Boltzmann method (spurious currents). In addition, physically significant simulation results for variable capillary numbers were calculated by studying the diffusivity of the interface between immiscible fluids in the Lattice Boltzmann method. Experiments and simulations of petrophysical measurements and simulation results from single-phase flow experiments were validated against each other and the possibilities of permeability simulation of digital rocks in different spatial directions were shown.
Applications include improved evaluation of reservoir properties in the deep geological subsurface such as production from porous hydrocarbon reservoirs, design of energy and geothermal reservoirs, and pressure management of porous reservoirs to prevent damaging earthquakes.

Prof. Dr. C. Hilgers, Dr. B. Busch, A.C. Monsees
Karlsruhe Institute of Technology (KIT), Faculty of Civil Engineering, Geosciences and Environmental Sciences, Institute of Applied Geosciences, SGT - Structural Geology & Tectonics

Prof. Dr. B. Nestler, Dr. A. Subhedar, A. Reiter
Karlsruhe University of Applied Sciences (HsKA), Institute of Materials and Processes, IDM - Institute for Digital Materials Research

Prof. Dr. M. Ziegler, M. Feinendegen, S. Biebricher
RWTH Aachen University, Faculty of Civil Engineering, GiB - Chair of Geotechnics in Civil Engineering and Institute of Foundation Engineering, Soil Mechanics, Rock Mechanics and Hydraulic Engineering
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