oa Fluid Phase Distribution in Haushi Reservoirs, North Oman: Insights from an Integrated Geological and Geochemical Analysis

Haushi reservoirs in North Oman exhibit diverse hydrocarbon fluid properties, with shallow accumulations dominated by biodegraded heavy oils and deeper zones showing unexpected fluid characteristics. This study integrates geological data, petroleum system analysis, petrophysics, PVT properties, and mud logging to identify key controls on fluid phase distribution.

Our findings highlight that the nature of incoming fluids (gas or oil) and the interaction between seal strength and closure height are the primary factors influencing phase behavior. Statistical analyses of petrophysical and mud gas data outperform traditional maturity maps, particularly in the Upper Gharif formations, where near-saturated conditions favor gas caps or oil rims.

Fluid distribution depends on charge composition: predominantly oil charges result in oil-filled traps unless near-critical or supercritical conditions apply, while mixed gas-oil charges lead to distinct phase behaviors—Class 1 traps are gas-dominated, Class 3 are oil-dominated, and Class 2 show mixed phases. Capillary seals and buoyancy pressures further dictate fluid retention, with tall traps, like those in Yibal, favoring oil dominance. These insights reinforce the need for an integrated approach considering migration fill-spill dynamics, seal strength, and closure height to predict hydrocarbon phases in Haushi reservoirs.