Producing Light Oil from a Frozen Reservoir: Reexamining Umiat Field, National Petroleum Reserve, Alaska
The Umiat field of the National Petroleum Reserve of Alaska (NPRA), discovered during the initial exploration of northern Alaska in the 1940’s and 50’s, consists of multiple reservoirs of consolidated shallow marine clastic rocks of the Cretaceous Nanushuk Formation deformed into a thrust-related anticline at the leading edge of the Brooks Range fold-and-thrust belt. The reservoirs are at very shallow depths (275-1250 ft); most are within permafrost. It is estimated that these reservoirs contain approximately 1.5 to 2.0 billion barrels of oil in place with 200-500 million barrels recoverable. Despite the shallow depths, the oil is high gravity (37°API) and not biodegraded. The initial discovery and delineation wells had low production rates due to low reservoir pressures, low GOR and permeability problems attributed to freezing of drilling fluids. These low production rates along with the lack of a drilling technology that could economically extract oil from such shallow, frozen rock have precluded Umiat development in the low oil price environment of the past.
Modern horizontal drilling techniques capable of accessing shallow reservoirs from a minimal surface footprint offer new options for economically drilling Umiat and similar fields. However, a production technique for a consolidated frozen reservoir with low GOR and reservoir pressures has not been identified. Because of the sub-zero temperature in permafrost, water injection in the reservoir is unsuitable because the injected water would freeze and occlude rock permeability. Possible methods being explored include oil displacement with cold gas injection, air injection and/or injection of a fluid with low freezing point to maintain reservoir pressure.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009