Fault analysis toolset aims to sharpen reserve estimates

The presence of faults in a reservoir creates a myriad of challenges for geoscientists trying to accurately identify and quantify reserves, but a new joint development program aims to bring reservoirs containing faults into sharper focus.

Gaz de France (GdF) and Foster Findlay Associates Ltd. (ffA) have entered into a collaboration aimed at developing a 3D fault analysis toolset that will provide operators with more accurate reservoir models and reserve estimates.

“In general, faults are badly imaged by seismic,” says Jonathan Henderson, Managing Director for ffA. “In areas surrounded by faults, many of the conventional seismic attributes are of doubtful validity and value.”

In light of this fact, the ffA/GdF joint program is designed to develop a 3D fault toolset that will enable appropriate analysis of the seismic data associated with and surrounding faults. Henderson is optimistic that the separate strengths of ffA and GdF will combine to provide more detailed understanding of a reservoir, even in the face of faults. “There is often sufficient information in 3D seismic data to provide evidence of potential fault sealing mechanisms such as cataclasis or clay smearing and to determine some of the physical properties of the imaged faults,” confirms Henderson.

Henderson is quick to point out that the collaboration is “not intended to deliver yet another bunch of seismic attributes that will add to the numerous (and sometimes useless) attributes that are commonly provided within the industry.” Rather, ffA plans to draw upon its experience in developing and commercializing 3D seismic image processing technology for the oil and gas industry to develop a set of tools that consider faults as volumetric entities, rather than 2D planes.

Says Henderson, “We will analyze the 3D geometries associated with faults that have been delineated as 3D geobodies. The tools being developed must be 3D-oriented, seismically driven and geostatistically constrained and, in consequence will be image-processing intensive.”

The tools will form a fault analysis workflow with 3 main stages:

• The first stage of the workflow is fault detection. Fault detection will utilize the FaultApp tools that are currently available in ffA’s SVI Pro, as well as the new fault imaging techniques that ffA is developing in parallel with the Fault Seal Analysis tool set. “The workflow will also be able to utilize manually interpreted faults,” says Henderson.

• The second stage of the workflow is delineation of the damage zone associated with a fault. “This has been the subject of the initial research phase of the project, and a number of techniques resulting from this work are undergoing evaluation at ffA,” Henderson adds. “Delineation of the 3D geometry of the fault damage zone as imaged within the seismic data will represent a major milestone in the project, as this defines the framework for constraining the detailed analysis of local fault properties.”

• The final stage of the workflow is to generate estimates of the fault sealing capacity associated with different sections of a fault. “This will utilize geostatistical techniques to provide a range of options for analyzing acoustic impedance or other seismically derived attribute data within and bounding the delineated 3D fault geometries,” adds Henderson.

For Gaz de France’s part, the production company believes that the 3D seismic attribute analysis tools will enable a greater understanding of the impact of faults on the distribution and extraction of hydrocarbons, supporting well placement and maximization of recovery.

Jean-François Dutzer, Geophysics R&D Manager at Gaz de France, HQ confirms this: “We believe the techniques being developed in collaboration with ffA will enable us to have a 3D understanding of the degree to which faults, as geobodies, may act as flow barriers. This can have a major impact on our exploration risking and development strategies and therefore on the economics associated with a reservoir.”

ffA’s team of seismic image analysis and software engineering experts will work with Gaz de France Affiliates from Britain, France, Norway, Germany and the Netherlands.

The project results will be first evaluated using seismic data from the UK Continental Shelf, an area in which Gaz de France has access to the well and engineering data required for validation. “However,” Henderson points out, “the aim of the project is to provide a set of fault seal analysis tools that are generally applicable to the greater exploration community.”

The tools will be commercialized by ffA and be available through ffA Services starting July 2007. They will be integrated into the January 2008 version of SVI Pro, ffA’s flagship product for processing and analysis of 3D seismic data.

For more information on the 3D fault analysis toolset being developed by ffA and Gaz de France, contact Jonathan Henderson at jhenderson@ffa.co.uk.