Reservoir Formation Fluid Equilibration & the Complexity of Contact Identification

Abstract Accurate hydrocarbon column identification is becoming increasingly challenging as we encounter more complex plays, both in terms of lithology and pore structure. In these environments, direct movable fluid measurement along with advanced interpretation techniques is essential for reducing uncertainty regarding fluid contacts and enhancing our understanding of reservoir fluid equilibrium. Gradient analysis applications are best utilized in intervals with good porosity, single phase, and relatively thick zones. The methods proposed in this paper utilize direct fluid measurement to confirm movable fluids, thereby overcoming the limitations of the conventional approach. A calibrated resistivity measurement is deployed to provide direct salinity calculations even in the presence of oil. The adopted workflow integrates real-time data to reconstruct saturation modeling and facilitate better identification of various fluid contacts. Finally, results were plotted with access pressure to indicate changes. A new reservoir fluid geodynamics technique was also used to confirm oil complexities beyond pressure gradient answers; such changes have little effect on gradient analysis. Results presented in this paper show an improved understanding of reservoir fluid variations. In a 150 ft thick interval, water and oil movement were identified throughout the layer. A direct fluid resistivity measurement was critical to this observation, confirming that the reservoir did not have enough time to equilibrate and establish a sharp oil-water contact. The gravitational forces were not sufficient to overcome capillary forces holding water high in the structure. Traditional gradient analysis confirms the presence of a gas-water contact, while the direct fluid measurement identified a small oil rim between the gas and the water. The gradient uncertainties window typically masks the small oil rim by increasing the gas density. PVT analysis confirmed fluid changes within the small interval. In the absence of gradient analysis, reservoir fluid geodynamics was utilized to confirm oil property variation with depth. The optical spectroscopy measurement indicated oil density increasing vertically during the real-time data gathering, results were later confirmed by laboratory PVT analysis. A novel residual pressure gradient analysis based on fluid density was used to anchor the pressure gradient trend to resolve the presence of two different fluids, result was confirmed by downhole fluid identification using optical spectroscopy measurement and later by laboratory analysis. Accurate direct downhole resistivity measurements were instrumental in reducing the unknowns in the Archie equation. The application of reservoir fluid geodynamics identified oil property variation to confirm reservoir filling and equilibration complexity real time