DE-FC26-08NT0005641

Goal
The goal of this project is to develop a robust reservoir model to test possible oil recovery methods that do not use steam or a liquid capable of freezing for the Umiat and similar frozen reservoirs. The results will provide important information concerning production methods for this and similar frozen reservoirs in northern Alaska and other arctic regions.

Performers
University of Alaska Fairbanks, Fairbanks, AK 99775-7320
Linc Energy Alaska LLC (Linc)

Background
The Umiat oil field in the Brooks Range foothills of northern Alaska contains light oil in a shallow, frozen reservoir. The Umiat field was discovered in the 1940s but was never considered viable because it is shallow, in the permafrost, relatively small, and far from any transportation infrastructure. Initial estimates of recoverable reserves in the Umiat field ranged from 30 to over 100 million bbl, with an average of about 70 million bbl. However, recent reserve estimates by private industry suggest that the accumulation may be considerably larger than originally thought, and modern horizontal drilling techniques now enable development of shallow reservoirs. This makes Umiat and similar fields in northern Alaska attractive exploration and production targets.

Little is known about how to produce conventional oil from a frozen reservoir. Most prior work has been on developing production techniques for heavy oil in unconsolidated but unfrozen sands, or for gas hydrates. There is no information available describing the behavior of a rock/ice/light oil system at low pressure. This information, along with a robust reservoir model, is needed to accurately model and evaluate the effectiveness of different production methods.

Impact
The Umiat field contains significant albeit unconventional (i.e., frozen) potential energy resources. This is a particularly attractive target considering the decline in the production of conventional oil resources from Alaska?s North Slope. Development of production methods and strategies for these shallow, unconventional resources will promote economically viable resource extraction. This project will encourage involvement of smaller exploration and production companies in Alaska by providing critical information not currently available to the public and by evaluating the applicability of existing production techniques. This information will increase the likelihood of successfully bringing smaller fields into production.

Accomplishments

Develop sedimentologic and stratigraphic model of the reservoir interval
Description of core taken during the original exploration program during the 1940s and ?50s was completed during the summer of 2010. Two weeks of field work during June and July 2010 focused on describing outcrops of the Umiat reservoir in the vicinity of Umiat field. Samples were also collected for diagenetic studies and pore structure analysis. Horizontal and vertical permeability was measured in major lithofacies in both core and outcrop.

Results of this work indicate that the Umiat reservoir is a complex system of shallow marine and distributary mouth bar sands with a strong vertical permeability anisotropy. Current work is focusing on linking permeability patterns with the observed lithofacies and facies associations in order to better predict permeability and permeability anisotropy across the field.

Develop structural model of reservoir
Examination of the existing Umiat core during the summer of 2009 showed that natural fractures are not abundant in these old vertical wells, probably because they are sparse, widely spaced, and/or steeply dipping. To address this issue, more emphasis is being placed on developing a structural model for the distribution of fractures by examining their structural context in more detail. Field work conducted during June and July 2010 examined both the structural geometry and the distribution of fractures on the Umiat structure and on a similar structure, the Big Bend anticline, that is nearby and well-exposed, the Big Bend anticline. Results of this work indicate that there are at least two major fracture networks present at the Umiat structure?one approximately perpendicular to the structure and a second approximately parallel to the structure. These fractures could play a major role in enhancing vertical permeability and vertical connectivity in a reservoir that is otherwise highly compartmentalized.

Characterization of reservoir and fluid properties
Data collection, including field work and description of remaining slabbed legacy Umiat core, has been completed.

An experimental apparatus was designed and constructed to conduct relative permeability experiments of oil and gas in the presence of ice. Preliminary results of experiments on both Berea Sandstone and samples of Umiat core demonstrate a significant reduction of oil relative permeability at irreducible water saturation caused by freezing of connate water. For Umiat samples, this decrease ranges from 39.3?91.5% with an average decline of 76.22%. This is significantly higher than the average 27% reduction reported by the Federal Bureau of Mines. The average decline of relative oil permeability at irreducible water saturation has increased almost three times by changing the freezing temperature from 26°F (-3.3°C) to 14°F (-10°C). This suggests that the reduction of the relative permeability is strongly dependent on the freezing temperature.

The relative permeability studies on the existing Umiat reservoir strongly indicate that the freezing temperature and void space structure play a large role in the permeability of the reservoir in the presence of ice. To further explore this issue, the experimental determination of the relative permeability of the Umiat reservoir was augmented by petrographic analysis of its pore structure, and Nuclear Magnetic Resonance (NMR) was used to study the pore-scale distribution of ice as temperature is incrementally decreased. These studies began during spring 2010 and will clarify when and where ice forms in the pore structure of the reservoir and have implications for the gas/oil relative permeability throughout the reservoir.

Compositional analysis and flow assurance studies on available samples of Umiat oil began in fall 2009. Analyses indicated that the total asphaltene content measured for Umiat dead oil is not significant, which suggests that Umiat oil does not have a high propensity for asphaltene precipitation. Lower asphaltene precipitation will lead to smooth production, no pipeline deposition and plugging (resulting in less pressure drop along the pipeline), and no change in composition.

Desktop reservoir simulation of proposed production strategies
A reservoir property model was constructed based on published data from Umiat field and subsequently modified to incorporate the new information regarding sand continuity and permeability anisotropy. These observations and petrophysical data indicate that the Upper and Lower Grandstand have distinct petrophysical properties and flow structures and should be treated separately.

A single realization of this geologic model using average observed porosity and Swi values yielded an estimated original-oil-in-place (OOIP) of approximately 1.52 billion barrels with 99 bcf of associated gas. A Monte Carlo simulation was conducted to evaluate the sensitivity of this OOIP value to a range of porosities, Swi, bulk volume, net-to-gross thickness ratio, formation volume factor, and gas content. The results of this simulation yielded OOIP estimations ranging from P10 of 750 million barrels, a P50 of 1550 million barrels and a P90 of 2474 million barrels.

Reservoir simulation studies are currently underway. The geologic model has been built, gridded, and initialized with the observed rock and fluid property values. The two major reservoir intervals, the Upper and Lower Grandstand sands, are being modeled separately because of different reservoir properties and computational time.

Ensuring optimum well placement is key for the economic development of any field. A wagon-wheel pattern is being used in the simulation as the most efficient means of accessing the maximum amount of the reservoir interval while minimizing the surface footprint. In the proposed pattern, one vertical well in the center along with two dual lateral injectors in the north and south at the top of the reservoir supports pressure for a combination of four dual lateral producers at the bottom of the interval, each one angled at 36 degrees in a square mile spike configuration. The wells have about 1000?1500 ft length of 4.5 inch open hole completion across the productive area with a total well length of 3000?3500 ft. To reduce surface impact and the cost of infrastructure, only 6?10 pad locations are being considered. A total combination of 64 producers and 24 injectors, controlled by flowing bottom hole pressures of 135 and 450 psia, respectively, will be used in the simulation model.

There is no indication of an active aquifer. Pressure support will be provided by injection of lean natural gas. Thermal equilibrium with the permafrost has to be maintained for wellbore stability and desired injectivity. Consequently, the gas will be injected at reservoir temperature of 26°F in order to avoid disturbing the permafrost.

Drilling Plans
Linc Energy is planning the first well in the Umiat field for the 2013/2014 drilling season.

Technology Transfer
UAF researchers have worked closely with Renaissance Alaska personnel throughout this project, sharing both data and interpretations. Teleconferences involving the entire research team are held quarterly.

During fall 2011, all UAF faculty and students participated in weekly one-hour seminars focusing on the implications of the ongoing geologic and engineering research on Umiat reservoir performance, drilling optimization, and production. Renaissance Alaska personnel participated in the seminasr via teleconference.

During the second year of the project, members of the team presented talks at the national meeting of the American Association of Petroleum Geologists (AAPG) and at the AAPG International Conference and Exhibition (ICE). In addition, a paper was submitted and accepted for the Arctic Technology Conference to be held in Houston, Texas in February 2011.

One M.S. thesis was completed in August 2010 and a second was completed in December 2010.

Current Status (December 2012)
Reservoir simulation studies are still being conducted. An updated project summary sheet will be provided in January/February 2013 based on draft final report findings.

Project Start: October 1, 2008
Project End: December 31, 2012

DOE Contribution: $1,350,652
Performer Contribution: $1,530,000

Contact Information
NETL - Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 281-494-2488)
UAF ? Catherine Hanks (chanks@gi.alaska.edu or 907-474-5562)
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