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Modelling Hydrocarbon Generation, Fluid Flow and Heat Transfer in Faulted Basins

I. Faille, P. Have, F. Willien, S. Wolf, M. C. Cacas, M. Thibaut, and J. L. Faure
IFP Energies Nouvelles, Rueil Malmaison cedex, France

We present a new basin simulator designed to better take faults into account, either as discontinuities controlling basin deformation and reservoir breaking, and as conduits or barriers to fluid flow. It computes hydrocarbon generation, fluid flow 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 structured 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. At basin scale, faults are geometrically represented by surfaces. Therefore, in the mesh, a fault is handled as two internal boundaries that can move relatively to each other when the fault is active. The mesh across a fault is then non-matching capturing correctly for the juxtaposition of different stratigraphical units.

Different models are proposed for fault behavior such as impervious fault, flow across fault or conductive fault. In the later case, the model couples a 3D flow model in the sedimentary layers with a 2D flow model along the fault surfaces that correspond to fluid flow along the fault zone. Petrophysical properties of the fault rock (e.g. permeability) are incorporated in the simulator as fault faces properties allowing a detailed description of the fault zone.

The calculator accounts for compaction, fluid flow through Darcy's law, conductive and convective heat transfer and hydrocarbon generation. It is based on a cell centered finite volume discretisation, which ensures conservation of physical quantities (mass of fluid, heat) at a discrete level and correctly handles heterogeneities. The numerical scheme is designed to manage 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.

Results on several semi-synthetic basins are already available (See Figures 1 and 2). They show the good behaviour of the calculator and illustrate its efficiency in handling faulted basins.

Figure 1: Synthetic basin, with alternatively shale and sand layers cut by several conductive faults. Arrows correspond to water flow field in the sedimentary layers. Figure 2: Same synthetic basin as Figure 1. Arrows correspond to the water velocities along the fault surfaces.


AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012