The difficulty in analyzing naturally fractured reservoirs has in the past been severely hampered by the application of old technology to this jambalaya of geologic, structural, and petrophysical features. Making sense of fractured reservoirs now requires the application of new analytical techniques in combination with computer analysis of the data.

There are two keys to understanding fractured formations like the Monterey Shale, Austin Chalk, or Nugget Sandstone. These keys are the use of full diameter whole-core samples in the analysis process and computerized data acquisition and reduction programs to prepare the results for evaluation and interpretation. Only recently has the capability to analyze 5-in. diameter cores been developed. Determination of all petrophysical properties is no longer limited to plug samples 1 in. in diameter.

The result has been a dramatic increase in the amount of information obtainable on reservoir properties. Permeability can now be measured in up to six horizontal directions versus one from plug samples. The flow capacity of specific fracture morphologies, such as partially mineralized, incipient, and natural open fractures, has been measured at simulated in-situ reservoir conditions. Experimental evidence indicates fracture permeability reductions of greater than three orders of magnitude occur in some lithologies.

By allowing the computer to prepare the time-consuming pole plots, rose diagrams, K vs. ^phgr crossplots, and geologic descriptions, the geologist is free to concentrate on analysis and interpretation of the prospect. This significantly improves their productivity and understanding of the reservoir and assists in identification of optimal locations for further drilling.

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