Characterization and fluid flow properties of frozen rock systems of Umiat Oil Field, Alaska

Abstract

The Umiat field, located in northwestern Alaska between the Brooks Range and the Arctic Ocean, potentially contains the largest accumulation of oil in Naval Petroleum Reserve No.4. Most of the oil is found within the permafrost zone. The main oil-producing zones in the Umiat field are marine sandstones in the Grandstand Formation of the Cretaceous Nanushuk group. Although the temperatures are close to freezing, the oil in the Umiat field remains unfrozen due to its very high API gravity. However, this results in a very unique pore space containing frozen water and oil, posing a particular challenge to characterization and measurement of fluid flow properties necessary for production. The unsteady-state gas-oil relative permeability measurement experiments were conducted in order to obtain critical information about the properties of two-phase fluid flow through the Umiat porous medium. Fluid flow experiments at 22°C and -10°C on representative core samples from the Umiat field showed 61% average decline in oil relative permeability as a result of freezing irreducible water. Capillary pressure measurement experiments were also carried out on selected core samples with an intention of characterizing their pore size distribution. Subsequently obtained data indicates fairly wide range of pore size for Umiat cores.