Production Methods for a Light Oil in a Cold Reservoir below Freezing Temperature: Umiat Field, National Petroleum Reserve, Alaska
Joanna Mongrain1, Abhijit Dandekar1, Vijay Bangia2, Catherine Hanks1, Allen Huckabay2, Paul McCarthy1, and Shirish Patil1
1University of Alaska Fairbanks, Fairbanks, AK.
2Renaissance Alaska, Houston, TX.
The Umiat field of the National Petroleum Reserve of Alaska (NPRA), a shallow (275-1055 ft/ 84-322 m) undersaturated oil field, was discovered in the 1940’s but has yet to be developed. The estimated OOIP is 1.5-2.0 billion stb, representing a considerable prize.
However, there are some technical challenges that must be overcome before development can proceed. Previous studies focused on solution gas drive as the primary drive mechanism despite the gas oil ratio and bubble point being unknown. If the GOR is low this will severely impede recovery. An additional challenge arises from approx. half of the productive interval being located within the permafrost. This limits the production mechanisms which may be applied e.g. not thermal or pressure maintenance by water injection. To enhance ultimate recovery, various pressure maintenance methods are being investigated.
A comprehensive engineering study is underway in tandem with a geologic study. The first part of the engineering study characterizes the effect of the reservoir being in permafrost on the rock and fluid properties. Of particular interest is the variation in relative permeability to oil as a function of temperature in the presence of connate water converted to ice at freezing temperatures. Due to capillary pressure effects it is anticipated that there will be a free water phase as well as a frozen water phase in the pores and the proportion of ice will vary with temperature. Experiments will determine the effect of this changing proportion of ice on the relative permeability to oil and the irreducible oil saturation. The location of the ice (in pores, on pore surfaces and/or pore throats) is expected to influence the flow dynamics in the reservoir.
The second part of the study combines these results with the geologic model in order determine an optimum production method for the Umiat field for a range of initial gas oil ratios. By comparing ultimate recoveries for different injection schemes and some more novel approaches, possible development scenarios will be developed and tested. This model will be augmented with more detailed geologic and engineering data as it becomes available.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia