Research paperEquation for defining hydrodynamic oil-water contact surface and an alternative approach, “structure surface transformation” for mapping hydrodynamic traps

- An equation defining a hydrodynamically tilted OWC surface is constructed from fundamental hydraulic principles.
- An alternative approach, “Structure Surface Transformation” for mapping hydrodynamic traps is presented.
- A field example from the Arabian basin is presented to illustrate the approach and the significance of hydrodynamic effect.

Flowing groundwater beneath an oil accumulation causes the oil-water contact (OWC) to be tilted. In this study we present an equation defining the surface of a tilted OWC: Zowc=ZOWC_0+ρw(ρw−ρo)(hw_0−hw) Where, ZOWC, ZOWC_0 are the depth of the OWC at a given location and a reference location (e.g. a well location), respectively; ρw, ρo are the density of formation water and oil, respectively; hw, hw_0 are the hydraulic head at the given location and the reference location, respectively. This equation can be used directly to delineate the tilted OWC of an oil accumulation. It can also be employed to map hydrodynamic traps. Based on the equation, an alternative approach, essentially the same as Hubbert's (1953) minimum energy level methodology, for mapping hydrodynamic traps is derived from an easy-to-understand concept, “Structure Surface Transformation”. A field example from the Arabian Basin is presented to illustrate the proposed approach for mapping hydrodynamic traps and the significance of hydrodynamic effect on trap size and volume. For this particular example, the traps' boundaries and volumes are significantly enlarged owing to a favorable hydrodynamic condition.