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

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

Godabrelidze, Vasil

Date: 2010-12

Type: Thesisms

Table of Contents: 1. Introduction -- 1.1. Previous research history and problem statement -- 1.2. Objectives -- 2. Background and literature review -- 2.1. Permafrost -- 2.2. Unfrozen water content -- 2.3. Absolute and relative permeabilities -- 2.4. Oil recovery from frozen reservoir rocks -- 2.5. Laboratory methods for determining absolute permeability -- 2.6. Laboratory methods for determining relative permeabilities -- 2.6.1. Steady-state technique -- 2.6.2. Unsteady-state technique -- 2.7. Capillary pressure measurement -- 3. Experimental work -- 3.1. Experimental setup -- 3.2. Experimental procedures for core flooding experiments -- 3.3. Experimental procedures for capillary pressure measurement experiments -- 3.4. Core samples -- 3.5. Test fluids -- 3.6. Experimental conditions -- 4. Results and discussion -- 4.1. Routine and special core analysis and subsequent results -- 4.2. Potential sources of error -- 4.3. Capillary pressure measurements and results -- 4.4. Discussion -- 5. Conclusions and recommendations -- References -- Appendices.

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.