A Novel Adaptive Gridding Approach to Hydrocarbon Migration Modelling

Oyvind Sylta and Are Tommeras
Migris AS, Trondheim, Norway

New approaches to basin scale hydrocarbon migration modelling may enable more accurate estimates of flow pathways, oil and gas losses and volumes trapped in undrilled prospects. These computer based methods may aid in constraining uncertainties and reducing exploration risk.

Most sedimentary basins include complex and dynamic geological features such as faults and salt bodies that may be best represented as non-regular mesh elements in computer simulators. Hydrocarbon migration flow patterns evolve through geologic time and we therefore propose to use dynamic meshes where each element in the mesh represents a section of a migration flow-path. The width and length of the individual hydrocarbon flow elements may typically be 30m and 200m, respectively. The hydrocarbon flow mesh is placed within a regular or non-regular structural mesh that represents the stratigraphic section during burial. The non-regular parts of the structural mesh are typically located along fault planes and salt domes. The stratigraphic mesh is subdivided vertically into flow-units in order to achieve a more realistic representation of flow in e.g. thin carriers and seals. This allows for using a Darcy flow approach with relative permeabilities and capillary pressures as functions of oil and gas saturations in the calculations of migration velocities, hydrocarbon saturations, column heights and migration losses within each migration flow-path.

The oil and gas flow-patterns within a subsiding basin can be studied in a 3D view as flow-rates or hydrocarbon saturations for each modelled time-step. Highlighting migration arteries may be an efficient technique for focusing exploration efforts, e.g. more detailed seismic mapping towards the prospective areas. Overall statistics of migration losses versus e.g. carrier permeabilities are useful for assessing the migration efficiencies at the basin level.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas