The project objective is to develop an explicit fracture simulator that can be used to model oil recovery from highly fractured formations and that uses available geologic input data on individual fractures.

National Energy Technology Laboratory Morgantown, WV

As conventional reservoirs are becoming depleted of hydrocarbon resources, it becomes more important to develop a knowledge base for unconventional reservoirs, such as highly fractured formations, so that the remaining oil-in-place can be recovered.

The current understanding of flow through highly naturally fractured formations is poor, and reservoir simulation capabilities for fractured reservoirs rely almost exclusively on techniques (e.g., dual porosity simulation) that smooth out the effects of individual fractures and fracture networks and ignore much of the available geologic data.

The goal of this project is to create a new generation of computer codes for oil and gas production to augment or replace codes written a generation ago and to create codes for which few antecedents exist. The project team’s contribution will include both 1) new flow codes and 2) new quantitative, predictive codes to provide better reservoir-specific input data for use in the flow codes. As appropriate, equations from experimental and theoretical physics and computational fluid dynamics, mechanics, and geomechanics will be incorporated to obtain more accurate and reliable simulators and simulations.

Results 
NETL’s in-house fractured-reservoir simulator will be modified to handle multi-layer, multi-component flows involving any two miscible fluids.

Benefits 
Publicly available, free modeling capability is provided by NETL. Model and updates are available on NETL’s website, providing a source for smaller, independent operators to model fractured reservoir recovery.

Summary 
The reservoir flow code will include explicit fractures (in place of dual permeability models) and physically realistic equations for flow through fractures (in place of parallel-plate fractures and flow), based on NETL studies of flow through real fractures. Ultimately, the completed NETFlow code will include explicit fractures in multiple geologic layers, multi-component sorption from the fluid(s), compositional tracking, and multiphase flow. As additional capabilities for use with more kinds of reservoirs are added, each code addition will be validated with data from the appropriate type of field.

Geomechanics and physics will be used with contemporary logs and geophysical data to improve NETL’s FRACGEN code for developing the geological models for input to NETFlow. Instead of unconditional statistical fits to field fracture data, finite-element mechanics will be used to calculate stress fields for subsequent prediction of fracture locations, orientations, and densities. NETL’s existing grain-level model for fracturing of sedimentary media will be extended for the prediction of fractures and fracture properties from the stress fields.

A potential long-term goal will be to remove the current universal relative-permeability assumption for multiphase flow through porous media and replace it with a reservoir simulator that makes the appropriate choice from among the flow regimes of viscous fingering, capillary fingering, relative permeability, and asymptotic approach to relative permeability.

Project highlights include the researchers:

• Improving equations of flow through fractured porous media by obtaining CT images of a real fracture geometry and performing computational fluid dynamic modeling of single-phase flow through it.
• Validating the NETFlow multilayer model with field data (March 2004).
• Developing and testing new computer code for compositional tracking of multiple components in the NETFlow simulation.
• Analyzing fundamental models and architecture needed for a coupled flow and geomechanical simulator.
• Using fracture geometries obtained by high-resolution, micro-CT imaging to extend volume-of-fluid computations of flow of immiscible, non-Newtonian fluids.

(July 2006) 
In the most recent project milestones, researchers have:

• Modification of NFFLOW modeling component continued. Researchers began testing the code on a realistic irregular network and modifying the code to include formation curvature. SUPERTRAPP software is being used to calculate the properties of mixed gases for different temperatures. The properties of methane and carbon dioxide are being studied so they can be incorporated into the NFFLOW reservoir simulator software. (May 2006).
• A major revision to the two-component multilayer version of NFFLOW has been completed. The process of assigning the correct effective composition to the flow rate calculation was improved. (July 2006).

$1,219,000

NETL – Sue Mehlhoff (sue.mehlhoff@netl.doe.gov or 918-699-2044)
NETL – Duane Smith (duane.smith@netl.doe.gov or 304-285-4069)

Publications 
Poster: “The Use of a Composition Dependent Pseudo potential in Reservoir Simulation”, Gordon Conference on Flow and Transport in Permeable Media at Proctor Academy, Andover, New Hampshire, July 30 – Aug 4, 2006.

“The Use of a Real-Gas Potential Approach in a Simulator for Highly Fractured Reservoirs”, Duane Smith, Neal Sams, Jerry Boyle for the CMWR XVI meeting in Copenhagen, June 2006.