Software models naturally fractured fields

The U.S. Energy Department said research it has funded soon will provide producers with software programs that improve capabilities to model the way fracture systems control the flow of fluids through a reservoir. Golder Associates, Redmond, Wash., has developed Discrete Fracture Network (DFN) modeling software to aid producers in understanding and exploiting fracture connectivity at the reservoir scale, an important factor in achieving optimum reservoir performance.

Feb. 2, 1998

4 min read

Golder Associates, Redmond, Wash., has developed Discrete Fracture Network (DFN) modeling software to aid producers in understanding and exploiting fracture connectivity at the reservoir scale, an important factor in achieving optimum reservoir performance.

DOE said by placing wells in densely fractured zones-located through DFN's modeling capabilities-producers can take advantage of efficient natural drainage systems to achieve maximum production.

As the lead researcher for the project, Golder is taking part in a seven-project research program on fractured-reservoir characterization and modeling that DOE's National Petroleum Technology Office funded in May 1996. DOE provided $743,000 of the project's $1.09 million cost.

The Golder project focuses on the problem of controlling fluid flow in a fractured reservoir at Yates field in West Texas.

DOE said water breakthroughs, inefficient channeling by fractures, and other factors often lead to reduced recovery or higher production costs.

Modeling research

"The average U.S. oil reservoir will produce about one third of the oil originally in place, while many reservoirs with naturally occurring fractures will yield only 10% of their reserves. This presents both a technical and a financial challenge for producers of marginal, naturally fractured reservoirs."

The Golder project was featured at a 2-day symposium in Denver on Jan. 19-20, sponsored by the Rocky Mountain Association of Geologists, DOE's Office of Fossil Energy, and six companies and/or industry associations.

The symposium reviewed the latest fracture modeling research methods available to increase production levels at these difficult sites.

DOE said fractured reservoirs are significant in several areas of the country-tight gas sands in the Rocky Mountain basins, fractured oil shale reservoirs in California and the Permian basin of Texas and eastern New Mexico, and the Austin chalk.

"Natural fractures occur extensively in reservoir rock formations throughout the Rocky Mountains. Modeling analysis based on improved knowledge of fracture location and characteristics allows producers in these reservoirs to design optimal recovery processes utilizing fluid flow paths that direct oil and gas toward production wells more efficiently and with less cost," DOE said.

Golder's DFN model portrays fractures and their connectivity differently from conventional fracture models, which do not explicitly model the geometry of discrete fractures, solution features, and bedding that control flow pathways.

The DFN software's interactive graphical system uses the producer's geologic, geophysical, and production data on fractures-compiled during field development-to explicitly model each fracture that is a major pathway for fluids.

DOE said, "This provides a more realistic picture of how fault-joint-fracture connectivity affects recovery processes and production by controlling reservoir fluid flow and also leverages the producer's cost to obtain the fracture data."

Field tests

Golder, Marathon Oil Co., and Massachusetts Institute of Technology are trying to validate the DFN modeling method at Yates field by simulating the tracer tests Marathon uses to track fluid movement through the reservoir.

Following validation, Golder will model Marathon's proprietary Thermally Assisted Gravity Segregation (TAGS) process, a cost-effective recovery method using injected steam to heat the oil and accelerate its movement through the fracture system.

DOE said the ability to simulate heat transfer through the fracture system will assist in developing reservoir-specific techniques for optimal TAGS steam injection, further demonstrating the DFN model's ability to predict fractured-reservoir processes.

Software programs developed within the project are posted to the project website, www.golder.com/niper/ niprhome.htm, so industry can use the software in other applicable U.S. reservoirs.

DOE said Golder will hold a workshop at the end of the project as part of the planned technology-transfer activities integral to DOE's cost-shared oil technology demonstration projects.

In the final phase of the project, Golder will analyze the financial benefits of applying DFN software in Yates field. Marathon is using project results to support drilling and completion activities in Yates Field this year.

DOE said Golder plans to extend the techniques developed in the project to additional reservoirs and other types of discrete layered rocky or sedimentary features as part of future research projects.