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2018 AAPG International Conference and Exhibition

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A Novel Methodology for 3-D Geo-Pressure Modeling: A Stochastic Approach

Abstract

The present-day overpressure distribution within sedimentary basins is linked to its burial history. In terms of overpressure generation and dissipation, the crucial issue is the development of rock and fluid state with time. This relates both to the matrix permeability itself, as well as to possible severe incidents like fracturing or opening of faults due to changed stress/pore pressure conditions. Similarly, such fractures and faults may also close with time, both mechanically, as well as due to cementation. Since the rock physical properties may change with time due to rock burial/uplift and accompanying diagenesis, as well as due to changes in stress/pore pressure conditions, it is necessary to employ an integrated methodology involving knowledge of burial history, lithology description and model processes. Basin modelling approaches are powerful tools that to a certain degree can simulate these processes. A pitfall is the vast number of input parameters, their inherent uncertainty, as well as the uncertainty of the model process itself. Several simulation input realizations may give same fits to observation data, hence the question of objectivity of the predictions is often the case. Stochastic approach should hence be the standard when performing basin modelling. An in-house pressure simulator has been re-developed with a combined Monte Carlo scheme. The simulator is customized to model pressure generation and dissipation in 3D over geological time scales. The basic assumption is that the fluid flow dynamics can be described by pressure compartments, defined by faults. The change in porosity is given by compaction curves, and kinetic equations reflecting the degree of chemical compaction. The tool quantifies pressure dissipation using a model for lateral cross-fault fluid flow and Darcy flow equations in the vertical direction. The Griffith-Coulomb failure and the frictional sliding criterion are used to simulate hydraulic leakage from the overpressured compartments. Apart from refining the numerical scheme, an improved approach for handling multiple cycles of erosion and deposition has been developed, with a corresponding logic for updating the sediment physical properties according the experienced burial history. The new simulator is applied on a data set in the North Sea. Controlling factors in model are sediment permeability, burial rate, and stress regime. The misfit between modelled and measured is used to rank the Monte Carlo simulations.