Using Monte Carlo models to predict hydrocarbon column heights and to illustrate how faults influence buoyant fluid entrapment

Abstract

Faults are often assumed to play a significant role in the migration and entrapment of hydrocarbons, either offering conduits for, or barriers to, fluid flow. They may also affect fluid-phase trapping and influence phase fractionation in the subsurface. A Monte Carlo modelling approach is used to model these effects for trap analysis. The aim is to show how varying fault seal capacity, the fault orientation, the regional stress tensor and the trap geometry can all affect how both oil and gas are retained within a trap. The model reduces the problem to a 1D analysis with a structural description depth-referenced to the crest of a prospect. Both juxtaposition and membrane fault seal are modelled, together with hydrodynamic effects and fault reactivation risk. The potential of a prospect to trap hydrocarbons is evaluated in a roll-up of results with the outputs including a predicted hydrocarbon column height distribution and column height control statistics. The technique also offers an insight into the potential fluid-phase partitioning that may occur dependent on the interplay between the active leakage mechanisms and spill control, enabling gas v. oil columns to be predicted. Thematic collection: This article is part of the Fault and top seals collection available at: https://www.lyellcollection.org/cc/fault-and-top-seals-2019