Coupling Geomechanical and Fluid Flow Modelling/ Effect of Reservoir Parameters on Solid Deformation

Geomechanical Modelling is part of the Reservoir simulation process and concerns
the calculation of the stress and strain field of the reservoir during depletion.
Although geomechanical modelling was seldom considered in the past in reservoir
simulation today it is crucial in determining porosity and permeability alterations due
to changing effective stresses which can affect oil production rate. These changes
occur as depletion mechanisms cause pore fluid pressure reduction and grain
redistribution due to fluid flow.
A detailed analysis of the various approaches to coupling the governing equations
of fluid flow and geomechanical deformation is being undertaken. The coupling
approaches are evaluated in terms of computational efficiency and accuracy of
convergence to the solution. The approaches are divided in four kinds: Fully implicit
coupling, iterative coupling, one way coupling and pseudocoupling. The choice of a
specific coupling strategy depends on the degree of accuracy required, the size and
the geometry of the mesh.
Also in our work a reservoir model is being simulated to check the accuracy of
analytical expressions for reservoir compaction and surface subsidence. Results
were in line with analytical solutions indicating that the assumption of material linear
elasticity and reservoir disk shape geometry is valid for the formulas. The simulation
results also showed that compaction rates are high at the start of the production
period due to material high compressibility and decreased with increasing production
time. Surface subsidence is approximately 1.4 times higher than subsurface
compaction which is attributed to the model long lateral dimensions and reservoir
exposure at the surface. By performing a sensitivity analysis we also show the
dependence of reservoir deformation on elastic material parameters of Young’s
modulus E and Poisson’s ratio ν. Subsurface compaction is influenced mainly by E
with ν having almost zero influence whereas surface subsidence is influenced almost
equally by both parameters.

By Georgios Neofytidis (September, 2014)