|Fluid and Rock Property Controls On Production and Seismic Monitoring Alaska Heavy Oils
||Last Reviewed 12/20/2012
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.
Colorado School of Mines, Golden, CO 80401
University of Houston, Houston, TX 77204
Earthworks, Newtown, CT 06470
BP, Anchorage, AK 99519
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.
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.
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.
The project team has made over 15 presentations at technical meetings (e.g., SEG, ACS, etc.). Five students completed graduate degrees and theses (two Ph.D. and three M.S.); two additional students are finishing thesis work. Two peer reviewed papers were published, several are under review, and several more will be completed in the last weeks of the project.
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. Asphaltene 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 -10 oC above 10,000 Pa (and frequency dependent). A complete set of “live” oil rheology experiments were completed. A large range of temperatures (-10 to 60°C) and pressures (15 to 2000 psi) were controlled and viscosity measured in novel high-pressure rheology setup.
A number of field trips to North Slope Alaska (January 2009, August 2010, November 2010, March 2012) were undertaken to coordinate sample/core retrieval, discuss objectives, and complete a sample testing plan with BP. Two presentations were given at the BP Heavy Oil Symposium in November 2010 with 150 people (from industry, academia, and government) attending in Anchorage, AK.
Development of the rock physics model continued with the addition of the Cold Heavy Oil Production Sands (CHOPS) hypothesis and an estimation of the properties of the wormholes for the Ugnu Formation. The model showed significant evidence of absorption due to the presence of the wormholes, suggesting the possibility of detecting small changes in the reservoir. The capacity of imaging such changes both in the amplitude spectrum and the image space has been quantified.
The Measured velocity-temperature trend on heavy oil sands suggests that the thermal damage to the sand frame is caused by thermal pressure of heavy oil. Thermal damage mainly occurs at low temperature and is reduced with increasing temperature. The thermal damage is limited by rock texture and degree of compaction. Analysis of measured data suggests that Gassmann’s model works well for heavy oil sands at temperature higher than the liquid point. The thermal damage effect on sand frame will need to be accounted for when modeling the velocity-temperature trend of heavy oil sands.
Current Status (December 2012)
All of the proposed project work has been successfully completed. The final report is available below under "Additional Information".
Project Start: October 1, 2008
Project End: June 30, 2012
DOE Contribution: $1,499,792
Performer Contribution: $400,000
NETL – Chandra Nautiyal (firstname.lastname@example.org or 281-294-2488)
Colorado School of Mines – Matthew Liberatore (email@example.com or 303-273-3531)
Final Project Report [PDF-2.82MB]