Accounting for the Effects of Lateral Stress in Basin and Reservoir Quality Modeling in a Compressive Tectonic Environment

Abstract

In quartzose sandstones with low thermal maturities, porosity evolution during burial is controlled primarily by effective stress (compaction). Many workflows assume that the effective stress may be approximated by the vertical effective stress (VES). This simplification is not appropriate in compressive (SH > Sh ≥ SV) or strike-slip (SH > SV ≥ Sh) regimes where horizontal stress components are equal to, or exceed, the vertical stress. Despite abundant published field evidence, many explorationists continue to underestimate sediment compaction in compressive regimes. In order to illustrate the problem, we: 1. estimated the magnitudes of the principal stress components using Anderson’s faulting theory, 2. transformed them into a single parameter - “equivalent mean effective stress (p*)”- using the Modified Cam Clay model. 3. applied p* in place of VES in the basin and reservoir modeling workflow. 4. calculated multiple porosity predictions in Touchstone™ for sand samples from NW Borneo assuming realistic compaction parameters and various modified VES histories. As a rough rule of thumb, rocks near reverse faults experience the highest lateral stress and their porosities are ~8 % (relative to bulk rock) lower than in normally compacted sediments. Increasing VES 2-3 times in existing modeling tools yields approximately correct porosities in this environment.