A New 3D Simulator for Modeling Fluid and Heat Flow in Faulted Basins

I. Faille, P. Havé, M. Thibaut, F. Willien, J. L. Rudkiewicz, and M. C. Cacas
IFP, 1&4 avenue de Bois Préau, 92852 Rueil Malmaison, France

To honor the geometries of faulted and tectonically complex basins, a new calculator is being developed. Its aim is to compute fluid flow, pressure and heat transfer on the 4D (space and time) geometry obtained by 3D volume restoration.

Contrary to classical basin simulators, this calculator does not require a mesh based on vertical pillars nor a multi-block structure associated to the fault network. The mesh follows the sediments during the evolution of the basin. It deforms continuously with respect to time to account for sedimentation, erosion, compaction and kinematic displacements. The simulation domain is structured in layers, in order to handle properly the corresponding heterogeneities and to follow the sedimentation processes (thickening of the layers). In each layer the mesh is unstructured: it may include several types of cells such as tetrahedra, hexahedra, pyramid, prism …however, a mesh composed mainly of hexahedra is preferred as they are well suited to the layered structure of the basin. Faults are handled as internal boundaries across which the mesh is non-matching: a fault is represented by two sets of connected boundary faces (i.e. face which have only one neighboring cell), one for the hanging wall and one for the footwall. Different models are proposed for fault behavior such as no flow across fault (impervious fault) or flow across fault.

The calculator solves for porosity, effective stress, pressure and temperature. In the current stage, lateral stresses are computed assuming that the ratios of lateral stresses over vertical stress are an input. Therefore, the considered equations are mass conservation of fluid, mechanical equilibrium, porosity/effective stress law and heat equation. The calculator is based on a cell centered finite volume discretization, which ensures conservation of physical quantities (mass of fluid, heat) at a discrete level and which accounts properly for heterogeneities. The numerical scheme handles the non matching meshes and guaranties appropriate connection of cells across faults. The calculator is written in C++, in a parallel object oriented approach which allows for flexibility while preserving computing performances. For instance, different finite volume schemes, including recent multi-points schemes, or linear solvers and preconditionners can be chosen.

Results on several semi-synthetic basins are already available. They show the good behavior of the calculator and illustrate its efficiency in handling complex geometries. Further developments are currently being performed which include in particular flow along faults.

AAPG Search and Discovery Article #90091©2009 AAPG Hedberg Research Conference, May 3-7, 2009 - Napa, California, U.S.A.