GEOSIM® is a coupled reservoir, geomechanics, fracturing and reservoir damage software for the analysis of reservoir problems which include strong coupling between reservoir flow and formation stress, deformations, compaction or stress-dependent properties, or interactions with fractures resulting from stimulation treatments, waterflooding or waste injection. The system is currently capable of modeling both single well and full field problems.
GEOSIM was originally developed at SIMTECH Consulting Services in early 1990s and later at Duke Engineering & Services (DE&S). It is now owned, developed, used for studies and leased by TAURUS. New products that have been released since 2003 include the version using Eclipse® simulator as the reservoir module, version with treatment of formation damage for sea water and produced water injection, and a pseudo-continuum rock mechanical model suitable for coupling to a dual-permeability reservoir model for naturally fractured reservoirs.
Typically, the reservoir grid is a subset of the finite element stress grid, which will cover the overburden, flanks and possibly base rock. Each component has its own input and, correspondingly, the user can build the model input data in several parts pertaining to the reservoir model (Eclipse or TRS), the stress-strain model and its interface (FEM3D and GEOINT), the fracture interface (GEOFRAC) and the damage module. Depending on the problem solved, only the relevant parts of the system need to be used.
GEOSIM has been used extensively for full field compaction studies, fault reactivation studies, waterflood and waste injection studies, and geomechanical modeling of conventional and thermal fracturing for a variety of reservoirs throughout the world.
Modeling of geomechanical response of the formation is performed by the GEOSIM module which consists of the stress analysis modules and the interface to TERASIM. The modular design allows optional stress codes to be utilized. Currently the principal module is the FEM3D code with the ENHANS 3 code as an option. FEM3D is a poroelastic and thermoelastic finite element code, which treats elasticity and plasticity. It also utilizes a Newton algorithm with variable stiffness scheme to handle general non-linear and elasto-plastic problems. Its features include:
Variety of fracture types and configurations can be represented in the model via the GEOFRAC module, as shown in Fig. 3 Fractures can be specified directly through data or imported from associated simulation through the SIMFRAC family of software. The features available include:
The above features apply to a continuum representation of the reservoir for the solid modeling. A separate option is also available to model deformation and permeability changes of fractured reservoirs. The main features are:
A void space within a continuum can be created by the cavity modeling option. The initial stiff material is switched to almost zero stiffness material and the respective confining stress is transferred to the elements surrounding the cavity region. The code also includes a procedure for weak modeling of sand production by combining the cavity, stress rebalancing options and fluid pressure gradient module. The quasi-static finite element model becomes evolutional when the fluid pressure gradient overcomes the confining forces at the sand face, through which propagating cavity is modeled
Several methods of coupling between the host reservoir model and GEOSIM stress model can be employed in order to optimize the performance of the system while representing the essential physics of the coupled processes. These range from the rigorous coupling between stress, flow and heat to loosely coupled treatment. Both the pore volume coupling (compaction or porosity enhancement) and coupling through flow properties (permeability changes due to stress or creation of fractures) can be represented. Some of the features available are:
Two methods of fracture coupling are available:
The damage caused by sea water or produced water is modeled by a relationship between permeability reduction and injected water throughput. Its features include:
The TERAPRO PC postprocessor is used to visualize the results of the simulation for the stress solution, and in case of the TERASIM reservoir model, also the flow solution. Its features include:
An example of the visualization of a subsidence study is shown below.
For visualization of the Eclipse reservoir flow results, user has a choice of using either the Eclipse postprocessing or TERAPRO, which can accept some Eclipse format files.
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