The Umiat field in northern Alaska is a shallow, light oil accumulation with an estimated OOIP of ~ 1.52 billion barrels with 99 bcf associated gas. The field was discovered in 1946 but was never considered viable because it is shallow, in the permafrost, and far from any infrastructure. Modern drilling and production techniques make Umiat an attractive exploration and production target. However, little is known about the behavior of a rock/ice/light oil system at low pressures. This information and a robust reservoir model are needed to evaluate the effectiveness of different production methods in this type of accumulation.Umiat consists of shoreface and deltaic Cretaceous sandstones deformed by a thrust-related anticline. New data indicate the reservoir has six facies associations with distinctive permeability trends. These trends combined with diagenetic effects and natural fractures impart a strong vertical and horizontal permeability anisotropy to the reservoir that needs to be accounted for in reservoir simulation.Understanding rock and fluid behavior under these conditions is critical for valid simulations. Experimental and theoretical studies indicate that there is a significant reduction in the relative permeability of oil in the presence of ice, with a maximum reduction when connate water is fresh and less reduction when water is saline. The small amount of available Umiat oil was severely weathered and limited traditional PVT and phase behavior analysis. A unique method was developed to physically recreate a pseudo-live reservoir oil sample by comparing the composition of the weathered Umiat fluid with a theoretical Umiat composition derived using the Pedersen method.These data are being integrated into a simulation model to test production techniques such as cold gas injection. Success at Umiat will pave the way for development of a unique class of Arctic reservoirs.

Shallow light oil accumulations in reservoirs within the permafrost are rarely recognized and, when identified, are often considered uneconomic because of their shallow depths and low reservoir energy. Horizontal drilling technology will improve the economics of these shallow accumulations, but a better understanding of the reservoir and fluid behavior under these low temperature and pressure conditions will improve recovery and lower development risk. However, little data is available on how a rock/ice/light oil system behaves at low pressures. This information and a robust reservoir model are needed to evaluate the effectiveness of different production methods in this type of accumulation. The Umiat field of northern Alaska was discovered in the 1940's and is a remote, shallow, light oil accumulation consisting of multiple deltaic and marginal marine Cretaceous sandstones deformed by a thrust-related anticline. While the accumulation may be significant (1.2 billion barrels OOIP), it is shallow and partly in the permafrost zone. New sedimentologic and structural studies indicate the reservoir has a complex permeability structure that will both impact both the placement of horizontal wells and subsequent reservoir performance. Reservoir sands generally consist of prograding wave-dominated shoreface deposits with good vertical permeability overlain by river-dominated deltaic deposits with poorer vertical permeability. Two different sets of natural fractures may also impart a strong permeability anisotropy to the reservoir. The temperature profile of the reservoir will also impact reservoir performance and will have to be incorporated into the reservoir simulation. Fluid flow experiments on samples of the Umiat reservoir at sub-freezing temperatures show a reduction in gas and oil relative permeability in the presence of interstitial ice, with the greatest reductions at lower temperatures. A representative Umiat oil sample has been recreated and used to calibrate an Equation of State (EOS) model that can then be used to predict the properties of a representative Umiat fluid in the simulation.

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