Can A Shallow Frozen Reservoir Be Successfully Exploited? A Predevelopment Case Study Of The Umiat Oil Field, Northern Alaska

摘要

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.