Exploration and Production Technologies
Naturally Fractured Reservoir Simulation Software Development

98-F014

Goal: To enhance and validate software developed by DOE for the characterization and modeling of gas flow in naturally fractured reservoirs.

Objective: To apply a new simulator to the analysis of a well test and to model a gas storage field. The code would be modified and improved to meet the challenges encountered during this real world application.

Performers:
Columbia Gas Transmission Company (CGT) – provided site, a new horizontal well, and data.
EG&G Technical Services of West Virginia, Inc. – data interpretation, code development, and simulation work.

Accomplishments:

  • Interpreted general fracture network pattern from CBIL fracture detection log and generated single layer 2-D fracture network realizations for purposes of well test analysis.
  • Successfully simulated a multi-rate drawdown/buildup well test. Determined that commercially estimated bulk reservoir permeability was greatly in error because it had included the permeability of a damaged zone around the well. Re-estimated bulk reservoir permeability without averaging over the damage zone.
  • Uniquely determined the fractional reduction of apparent fracture apertures within the damaged zone around the well bore and the distance around the well bore where the damage occurs.
  • Developed software and technique for modeling partial obstruction of fractures within a zone around the well bore. This process replaces the usage of a “skin factor” and provides a better physical representation of the damage around the well bore resulting from the invasion of drilling mud or fluids.
  • Developed software for multi-layer fracture network modeling, and began software development for multilayer flow simulations.

Two computer codes, a fracture network generator and a single-phase gas flow simulator, were written at NETL to improve our modeling capabilities for the naturally fractured reservoirs that conventional, dual-porosity (sugar-cube) models can not adequately represent. The code software was tested using data from a storage field owned by Colombia Gas Transmission Company (CGT). The work began with an attempt to simulate a multiple-rate drawdown/buildup test on a new horizontal well that had been logged with a fracture detection tool. The results from the work were used to direct additional code development. Later, work began on an attempt to simulate reservoir performance in the southern half of a gas storage field.

Data from a fracture detection log was interpreted and used to create a single layer representation of the fracture network surrounding the well. Initial simulation efforts to match the well test results were disappointing. Subsequently, code was added to permit rapid alteration of the fracture apertures within a zone around the well bore. This additional code solved the problem and permitted a good simulation match. More importantly, the new code permitted the modeler to find a unique estimate of the width of the zone of fracture obstruction around the well bore plus the average reduction factor for fracture apertures within this zone.

One of the primary goals of this project was to develop code for multilayer reservoir simulations. The fracture network generator was successfully modified to produce up to ten layers, but the modifications to the flow simulator suffered from one or more bugs in the code.

Current Status and Remaining Tasks: This project has been completed. The Final Report from this 5-year research project "New and Novel Fracture Stimulation Technologies for the Revitalization of Existing Gas Storage Wells" is available on CD-ROM through the NETL CD ordering system.

Project Start Date: January 28, 1998
Project End Date: January 28, 2002

DOE Contribution: $100,000
Performer Contribution: $740,000

Contact Information:
Columbia Gas Transmission - Richard Fulcher (304-357-2889 or rfulcher@columbiaenergy.com)
NETL - Jim Ammer (304-285-4383 or james.ammer@netl.doe.gov)

 

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