Integrated Trap and Seal Evaluation of Complex Reservoir Systems

Davis, J. Steven¹, Francesco V. Corona², Peter J. Vrolijk³, Bill R. James⁴ (1) ExxonMobil Exploration Co, Houston, TX (2) ExxonMobil Development Co, Houston, TX (3) ExxonMobil Upstream Research Co, Houston, TX (4) ExxonMobil Upstream Research Co, Austin, TX

Regardless of upstream business stage, complete understanding of fluid distributions and plumbing in complex hydrocarbon reservoirs requires integration of fluid properties, bed seal properties, fracture gradients, and structural and stratigraphic models. Successful integrated trap analysis requires simultaneous evaluation of the multiple elements that control contact distributions. Traditional one element analyses (e.g., fault seal analysis) run the risk of forcing improbable solutions.

Reservoir Connectivity Analysis (RCA) is an integrative methodology for analyzing hydrocarbon distributions in complex reservoir systems. RCA relates known or predicted fluid contacts 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 structural and stratigraphic connections. Barriers to communication within a reservoir system include internal seals, base seal draped across a structure in a given reservoir, and faults.

RCA has been successfully applied to hydrocarbon traps worldwide. An example demonstrates application of RCA 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. RCA 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 recent interference tests across the faults.