Heavy and Thermal Oil Recovery Production Mechanisms

DE-FC26-00BC15311

Program
This project was selected in response to DOE's Oil Exploration and Production solicitation DE-PS26-01NT41048 (focus area: Heavy Oil and Thermal Recovery). The goal was to improve understanding of heavy oil reservoirs and to develop innovative technologies to produce heavy oil.

Project Goal
The emphasis of this work was to investigate the mechanisms and factors that control the recovery of heavy oil under primary and enhanced modes of operation. The ultimate objective was to provide the technical underpinnings needed to improve reservoir recovery efficiencies.

Performer
Stanford University
Stanford, CA

All work was completed at Stanford University. Industry participants over the life of the project were Aera Energy LLC (Bakersfield, CA), ChevronTexaco Technology Co. (San Ramon, CA), ConocoPhillips (Houston, TX), ExxonMobil Corp. (Houston, TX) Petroleos de Venezuela SA (Caracas, Venezuela), Shell International Exploration & Production (Houston, TX), Total (Paris, France), and Tyco Thermal Controls (Menlo Park, CA).

Project Results
The project laid the technical foundations for thermal oil recovery from low-permeability, fractured porous media as well as primary heavy oil recovery using the solution gas drive mechanism. Additionally, in situ upgrading of heavy oil was shown to be feasible using in situ combustion. The project also examined the efficiency of reservoir heating using horizontal and multilateral wells. Finally, improved reservoir definition techniques were developed to infer reservoir heterogeneity from production data.

Benefits
Thermal recovery, accomplished primarily by injecting steam, is the most successful enhanced oil recovery (EOR) process. This project furthered the application of steam injection by lending support to the technical case for thermal recovery from low-permeability fractured formations, such as diatomite. Diatomite formations in California alone contain 12-80 billion bbl of original-oil-in-place (OOIP), and steam successfully unlocks these resources. Several companies are moving ahead with steam injection pilots and projects in diatomite partially as a result of this research. The industry, state of California, and nation would benefit from increased production, royalty, and tax revenue.

Background
Despite the finite nature of petroleum and gas, they remain dominant sources of energy. This appears unlikely to change in the near future. Against this backdrop of increasing reliance on imported oil, heavy oil (10-20° API or 940-1,000 kg/m3) is a tremendous energy resource that is not utilized to its fullest potential. In the contiguous U.S., it is estimated that heavy oil reservoirs hold in excess of 85 billion barrels of OOIP; in Alaska there is at least an additional 40 billion barrels. Worldwide, there are also large heavy-oil deposits in Canada, Venezuela, China, Indonesia, and the former Soviet Union. Moreover, fractured reservoirs are estimated to contain 25-30% of the world's oil supply. Many of these reservoirs, with artificial or natural fractures, contain medium to heavy oil or tar. The central problem with heavy crude oil production is that the oil is far more viscous than water or conventional crude oil. Because fluid flow resistance is proportional to viscosity, high viscosity frustrates production. The challenge was to improve industry's understanding of primary and thermal heavy oil recovery mechanisms and to increase recovery efficiency so that oil not producible by conventional means can be recovered. Thermal methods, especially steam injection-where heat is used to lower oil viscosity-and carefully engineered primary (cold) production, are the best techniques for increasing production from heavy and fractured reservoirs.

Project Summary
The project:

• Developed a new technique for measuring the oil-water relative permeability and capillary pressure characteristics of heavy oil in porous media.
• Proposed and verified a mechanism for the evolution of the wettability of reservoir rock toward increased water wetness as a function of increasing temperature.
• Proved experimentally, the theoretical existence of two different modes of countercurrent imbibition in multidimensional fractured rock. This discovery led to a time-dependent formulation of the matrix-fracture transfer function employed in dual-porosity simulation.
• Demonstrated that, with respect to heavy oil solution gas drive, oil viscosity and composition affect significantly the coalescence of gas liberated from solution into a continuous gas phase. Thus the gas remains dispersed and relatively immobile within the reservoir, thereby maintaining drive energy for a significant period of time. This observation explains, in part, the excellent recovery witnessed in some heavy oil reservoirs under cold production.
• Developed a novel technique employing streamlines to perform history matching of production data under geological constraints.

Current Status (October 2005)
A small business, StreamSim Technologies, is attempting to commercialize the history-matching technique developed under this project. The company expects to be marketing a commercial code within 3 years.

Publications
Final Report  [PDF-5.59MB] - December, 2003

Hoffman, B.T., and Kovscek, A. R., "Displacement Front Stability of Steam Injection into High Porosity Diatomite Rock," Journal of Petroleum Science and Engineering, 46(4), 253-266 (2005). DOI:10.1016/j.petrol.2005.01.004.

Schembre. J.M., and Kovscek, A.R., "Thermally Induced Fines Migration: Its Relationship to Wettability and Formation Damage," SPE 86937, Proceedings of the SPE International Thermal Operations and Heavy Oil Symposium and Western Regional Meeting, Bakersfield, CA, March 16-18, 2004.

Tang, G.Q., and Kovscek, A.R., "An Experimental Investigation of the Effect of Temperature on Recovery of Heavy Oil From Diatomite," Society of Petroleum Engineers Journal, 9(2), 163-179 (2004).

Sahni, A., Gadelle, F., Kumar, M., Tomutsa, L., and Kovscek, A.R., "Experiments and Analysis of Heavy Oil Solution Gas Drive," Society of Petroleum Engineers Reservoir Engineering & Evaluation, 7(3), 217-229 (2004).

Kovscek, A. R., and Bertin, H.J., "Foam Mobility in Heterogeneous Porous Media I & II: Scaling Concepts" & "Experimental Observations," Transport in Porous Media, 52, 17-35, 37-49 (2003).

(A list of additional published articles can be obtained from the principal investigator at kovscek@pangea.stanford.edu.)

Project Start: September 1, 2000
Project End: December 31, 2003

DOE Contribution: $1,453,137
Performer Contribution: $363,284 (20% of total)

Contact Information
NETL - Sue Mehlhoff (sue.mehlhoff@netl.doe.gov or 918-699-2044)
Stanford U. - Anthony Kovscek (kovscek@pangea.stanford.edu or 650-723-1218)

Water saturation

CT-derived water saturation images of water imbibition in oil-saturated core of diatomite. Times beneath the images are given in minutes.