DE-NT0005663

Goal
The goal of this project is to improve recovery of Alaskan North Slope (ANS) heavy oil resources in the Ugnu formation by improving our understanding of the formation’s vertical and lateral heterogeneities via core evaluation, evaluating possible recovery processes, and employing geophysical monitoring to assess production and modify production operations.

Performers
Colorado School of Mines, Golden, CO 80401
University of Houston, Houston, TX 77204
Earthworks, Newtown, CT 06470
BP, Anchorage, AK 99519

Background
Although the reserves of heavy oil on the North Slope of Alaska are enormous (estimates are up to 10 billion barrels in place), difficult technical and economic hurdles must be overcome to produce them. The Ugnu formation contains the most viscous, biodegraded oils and standard production methods are ineffective. Numerous alternative techniques for heavy oil production have been proposed (e.g., steam injection). However, the overall effectiveness of these methods is much lower than either modeling or laboratory tests suggest. A prime factor limiting the efficiency of heavy oil recovery is the heterogeneity of the system. Heavy oils are viscoelastic materials with varying resin and asphaltene contents. The rocks containing the fluids have porosities, permeabilities, connectivities, and mineral contents that vary over short distances.

Seismic attributes could be used to monitor how well a recovery technique is sweeping the reservoir and where there are complications. Seismic responses from pre-production of the reservoir could be used to illuminate the local geology, which could assist in designing well trajectories that would enhance productivity.

This project will characterize the fluids and rocks on a fine scale to ascertain the range and distribution of physical properties and evaluate the various proposed recovery processes in light of these distributions; design a geophysical monitoring program to continually assess the progress and effectiveness of production; and develop feedback procedures using monitoring results to update and modify the production procedures.

Impact
A state-of-the-art seismic monitoring program based on chemical and physical characterization of core samples and simulated production experiments has potential to improve the technological and economic hurdles slowing development of the vast heavy oil resource on the North Slope of Alaska. The proposed project will generate significant amounts of new public data on the seismic attributes of ANS oils and reservoir rock. This work is expected to improve seismic resolution through permafrost and the ability to evaluate heavy oil reservoirs. Successful completion of the project will result in the capability to monitor, over time, the progress of a heavy oil recovery process by seismic measurements.

Accomplishments
Results of the rock physics model, and algorithms developed for modeling seismic data at a high frequency range were presented at the 1st International Rock Physics Symposium in Colorado (August 2011).

Researchers collected samples that included approximately a dozen dead oil samples, 5 gallons of dead oil, 5 gallons of oily sand, and several well logs. In addition, samples from two different cores have been sampled. Several types of molecules were observed by MBMS, and NMR in the heavy oil samples including alkanes, alkynes, aromatics, as well as a small amount of other type organic molecules. These molecules vaporize in the sequence of alkynes, alkanes, and aromatics as the temperature increases. The average detected molecular weights vary between 140 and 300 Daltons. Azeotrope of water and alkyne or cyclohexenetype molecules has been detected by the congruent of water clusters and the olefin MS peaks between 200-300 ºC.

Two students completed their M.S. theses (one in Petroleum Engineering, one in Chemical Engineering) and one student is completing his Ph.D thesis during the fall 2011 semester.

Saturate-Aromatic-Resin-Asphaltene (SARA) fractions have been measured on site and by an outside laboratory. The SARA technique has large experimental variation when used to measure heavy oils. Asphlatene content varied from 3 to 9% in the same sample measured by CSM and an outside laboratory. More powerful chemical characterization techniques are being pursued.

The oils (including more than 18 oil, oil/sand, oil/water, and oil/sand/water mixtures) exhibited non-Newtonian characteristics, including shear thinning and a non-zero shear modulus. The complex viscosity of the dead oils has been found to be as high as 7,000 Pa-s and a shear modulus at -10oC above 10,000 Pa (and frequency dependent).

A large number of experiments have been completed to date, including molecular beam mass spectroscopy (MBMS), optical and scanning electron microscopy, x-ray CAT scans, and laboratory seismic measurements. For example, the microscopy has allowed the sand grain size to be determined (~5µm diameter) as well as the grain chemistry (nearly pure silica).

The Project Management Plan (PMP), Technological Assessment, and Project Summary have been completed in cooperation with NETL. A number of trips to Alaska (January 2009, August 2010, November 2010) were undertaken to coordinate sample/core retrieval, discuss objectives, and complete a sample testing plan with BP. Two talks by the group were made at the BP Heavy Oil Symposium in Anchorage, AK in November 2010 with 150 people (from industry, academia, and government) attending.

A micrograph (from the ESEM) of clean sand showing grain sizes from ~0.1 mm to 2 mm.

Current Status (October 2011)
Work on geochemical analysis of produced oil samples and rheology on a matrix of oil/sand/water mixtures, and data collection is ongoing to meet the project goal and assist researchers in completing the project. Rock property measurements are underway. Chemistry signatures are being used in the analysis of the MBMS and SARA data to help understand the viscosity of the heavy oils. Future research may be performed on the heavy oil samples to provide comprehensive structural information of the heavier oil parts such as bitumen.

Development of the rock physics model continues with the addition of the Cold Heavy Oil Production Sands (CHOPS) hypothesis and estimation of the properties of the wormholes for the Ugnu formation. The model showed significant evidence that absorption due to the presence of the wormhole can be modeled, suggesting the possibility of detecting small changes in the reservoir, and the capacity of imaging such changes both in the amplitude spectrum and the image space.

Project Start: October 1, 2008
Project End: June 30, 2012

DOE Contribution: $1,499,792
Performer Contribution: $400,000

Contact Information:
NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 281-294-2488)
Colorado School of Mines – Matthew Liberatore (mliberat@mines.edu or 303-273-3531)
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