Coupled geomechanics and flow simulation for time‐lapse seismic modeling

Abstract

To accurately predict production in compactible reservoirs, we must use coupled models of fluid flow and mechanical deformation. Staggered-in-time loose coupling of flow and deformation via a high-level numerical interface that repeatedly calls first flow and then mechanics allows us to leverage the decades of work put into individual flow and mechanics simulators while still capturing realistic coupled physics. These two processes are often naturally modeled using different time stepping schemes and different spatial grids-flow should only model the reservoir, whereas mechanics requires a grid that extends to the earth's surface for overburden loading and may extend further than the reservoir in the lateral directions. Although spatial and temporal variability between flow and mechanics can be difficult to accommodate with full coupling, it is easily handled via loose coupling. We calculate the total stress by adding pore pressures to the effective rock stress. In turn, changes in volume strain induce updates to porosity and permeability and, hence, dynamically alter the flow solution during simulation. Incorporating the resulting time-dependent pressures, saturations, and porosities (from coupled flow and mechanics) into Gassmann's equations results in seismic wave velocities and densities that can differ markedly from those calculated from flow alone. In a synthetic numerical experiment based on Belridge field, California, incorporation of coupled flow and mechanical deformation into time-lapse calculations produces compressional wave velocities that differ markedly from those produced by flow alone. In fact, it is the closing of the pores themselves (reduction in permeability) in this example which has the greatest impact on fluid pressures and saturations and, hence, elastic wave parameters such as velocity.

Structure‐coupled multiphysics imaging in geophysical sciences

“…For example, there are significant uncertainties in the quantitative analysis of only time-lapse seismic measurements over petroleum reservoirs [Landrø, 2002;Furtney and Woods, 2006;Tsuneyama and Mavko, 2007]. Yet it is observed that fluid withdrawal from a reservoir may be associated with geomechanical deformations (especially in weak rock formations) and seismic time shifts [e.g., Minkoff et al, 2004;Hatchell and Bourne, 2005;Aarre, 2006;Rickett et al, 2007]. An established physical method for imaging or monitoring subterranean fluid flow processes is the spontaneous polarization method [e.g., Kemna et al, 2004], and changes in reservoir porosity, pressure and fluid saturation computed using coupled fluid flow and geomechanical deformation modeling can be used to determine changes in density and seismic velocities with time [Minkoff et al, 2004].…”

“…Yet it is observed that fluid withdrawal from a reservoir may be associated with geomechanical deformations (especially in weak rock formations) and seismic time shifts [e.g., Minkoff et al, 2004;Hatchell and Bourne, 2005;Aarre, 2006;Rickett et al, 2007]. An established physical method for imaging or monitoring subterranean fluid flow processes is the spontaneous polarization method [e.g., Kemna et al, 2004], and changes in reservoir porosity, pressure and fluid saturation computed using coupled fluid flow and geomechanical deformation modeling can be used to determine changes in density and seismic velocities with time [Minkoff et al, 2004]. It is thus logical to expect that fully coupled 3-D fluid flow and geomechanical deformation simulations and seismic modeling, linked with spontaneous potential and/or induced polarization modeling using the cross-gradients approach, would be a useful way forward in time-lapse analysis.…”

On the propagation of a disturbance in a heterogeneous, deformable, porous medium saturated with two fluid phases

“…We assume that one can model the actual field history incrementally, modeling any rapid transient disturbance in pressure and solid displacement using the equations derived here and modeling the saturation changes using quasi-static two-phase flow. As in a loosely coupled approach to modeling deformation and flow (Minkoff et al, 2003(Minkoff et al, , 2004, one can introduce feedback between the solution to the poroelastic equations derived here and the reservoir simulator used to model the long-term saturation changes. This should become clearer after we introduce the full set of coupled equations for two-phase flow.…”

“…A numerical method is the most general, and there are several studies based upon numerical techniques (Noorishad et al, 1992;Rutqvist et al, 2002;Minkoff et al, 2003Minkoff et al, , 2004Dean et al, 2006). Numerical methods can require significant computer resources -CPU time and computer memory.…”

Perturbation methods for two special cases of the time‐lapse seismic inverse problem

“…Practical means to cope with preprocessing issues particular to the time-lapse problem, such as redatuming (Winthaegen, Verschuur, and Berkhout 2004), image registration (Fomel and Jin 2009), and discrimination of target versus acquisition variations (Berkhout and Verschuur 2007); represent open and active areas of research. Other research areas, for instance time-lapse geomechanics (Minkoff et al 2004), also impact seismic methods, but in this paper we will focus on the above list.…”