Coupling Pore-Pressure and Stress Modeling: An Approach to Model Stress Impact from Faults

Arnt Grøver
Sintef Petroleum Research, Trondheim, Norway

Within petroleum exploration it is of crucial importance to handle the coupling between pore-pressure and stress in sedimentary basins. Commonly used fracture criteria have a strong dependency on these two properties because it quantifies the timing and location of hydraulic leakage which influence the fluid migration pathways through geological time.

The fluid flow and stress analysis is usually handled separately in basin modelling applications. A standard way is to model the vertical stress as the weight of the overburden, and then relate the minimum horizontal stress to the vertical component through empirical equations. The minimum horizontal stress is then used together with the pore pressure to evaluate fracture criteria for hydraulic leakage. It is known that high stress concentrations can arise around faults in tectonic environments and that the vertical stress component occasionally no longer is the maximum principle stress. Reactivation of faults might also trigger fluid flow/leakage along the faults. This paper presents an approach to model stress impact from faults and fault interactions, coupled together with a pressure simulator on basin scale, through geological time.

The pressure simulator use extended fault traces to define the reservoir units to pressure compartments. It then performs pressure generation within and dissipation between the pressure compartments. The 3D flow pattern on a geological time scale and the resulting pressure distribution are modelled. Processes included are shale compaction, shale drainage, quartz cementation, lateral flow and hydraulic leakage. The stress model used is based on the theory of angular dislocation in an elastic half-space. It is a boundary element method (BEM). The polygonal elements (dislocations) define the fault surfaces. The pore-pressure gradients between the pressure compartments are used as loads to the stress analysis. The stress output is then used to evaluate possible leakage. This loop of work described above is carried out together with the other processes within the simulator through geological time until present day.

The approach presented here has a goal of getting a better picture of the fluid migration pathways through geological time, and can be used in basin modelling to evaluate exploration risk in undrilled prospects.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands