INTEGRATED TRAP AND SEAL EVALUATION OF STRUCTURALLY COMPLEX RESERVOIR SYSTEMS

Complete understanding of fluid distributions and plumbing in complex, multi-phase, hydrocarbon reservoirs requires integration of structural and stratigraphic models, fracture gradients, fluid properties, and bed seal properties. Successful, fully-integrated trap analyses make use of simultaneous evaluation of the multiple elements that control hydrocarbon fluid distributions. Traditional single element analyses (e.g., fault seal analysis only) commonly run the risk of forcing improbable solutions.

The integrative methodology for analyzing hydrocarbon distributions in complexly deformed reservoir systems relates known or predicted fluid fill levels to fluid properties (e.g., geochemistry, pressure), bed seal properties (e.g., capillary, mechanical), and a reservoir container topology. The reservoir container topology comprises the shapes of the reservoir volumes and their connections – both structural (e.g., fault juxtaposition) and stratigraphic (e.g., channel erosional cuts). Barriers to communication within a reservoir system include low transmissibility faults and internal seals, and base seal draped across a structure for a given reservoir.

We present an example that demonstrates application of an integrated analysis to a complex channel system draped across an intensely faulted anticline. The trap has a single gas-oil contact, but across the structure the oil-water contacts are offset by several hundred meters. Our analysis shows that the hydrocarbons are in pressure communication, but the aquifers are separated by the base seal. The oil-water contacts are controlled by the spill and base seal, and the gas-oil contact by capillary entry pressure of the top seal. Thus, the faults do not constitute flow barriers (i.e., seals) over geologic time, a prediction validated by well tests across the faults.