AAPG Bulletin

Abstract

AAPG Bulletin, V. 98, No. 3 (March 2014), P. 563585.

DOI:10.1306/08201313011

Integrated reservoir characterization and simulation of a shallow, light-oil, low-temperature reservoir: Umiat field, National Petroleum Reserve, Alaska

Catherine L. Hanks,1 Grant Shimer,2 Iman Oraki Kohshour,3 Mohabbat Ahmadi,4 Paul J. McCarthy,5 Abhijit Dandekar,6 Joanna Mongrain,7 Raelene Wentz8

7Shell International Exploration and Production Inc., 200 North Dairy Ashford, Houston, Texas 77079-1197; Joanna.Mongrain@shell.com
8Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska 99775; present address: Exploration Department, Sumitomo Metal Mining Pogo LLC, Delta Junction, Alaska 99737; Raelene.Wentz@smmpogo.com

ABSTRACT

Umiat field in northern Alaska is a shallow, light-oil accumulation with an estimated original oil in place of more than 1.5 billion bbl and 99 bcf associated gas. The field, discovered in 1946, was never considered viable because it is shallow, in permafrost, and far from any infrastructure. Modern drilling and production techniques now make Umiat a more attractive target if the behavior of a rock, ice, and light oil system at low pressure can be understood and simulated.

The Umiat reservoir consists of shoreface and deltaic sandstones of the Cretaceous Nanushuk Formation deformed by a thrust-related anticline. Depositional environment imparts a strong vertical and horizontal permeability anisotropy to the reservoir that may be further complicated by diagenesis and open natural fractures.

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. A representative Umiat oil sample was reconstituted by comparing the composition of a severely weathered Umiat fluid to a theoretical Umiat fluid composition derived using the Pedersen method. This sample was then used to determine fluid properties at reservoir conditions such as bubble point pressure, viscosity, and density.

These geologic and engineering data were integrated into a simulation model that indicate recoveries of 12%–15% can be achieved over a 50-yr production period using cold gas injection from five well pads with a wagon-wheel configuration of multilateral wells.

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