Hydraulic Fracture Diagnosis Using Tracers

by
Christoffel Josephus Gardien, MSE

University of Texas at Austin, 1996
Supervisors: Gary A. Pope
A. Daniel Hill

This research explores the application of tracer technology to estimate hydraulic fracture parameters. Existing methods for hydraulic fracture diagnosis (e.g. well logging and pressure transient testing) often do not provide accurate or unique solutions, so improved methods are needed. The principle behind the use of tracers for hydraulic fracture diagnosis is the dominance of the fracture on the flow field in a hydraulically fractured reservoir and the strong influence of fracture parameters on the flow filed. This will be reflected in the tracer response curves of a single-well tracer test in a hydraulically fractured well, making the tracer test diagnostic of the fracture and its parameters.

Several kinds of tracers (conservative, sorbing, reactive and partitioning) have been tested for their diagnostic value by numerical modeling. The major factors of influence on the tracer response have been identified. These factors are combined in a ratio, the tracer influence ratio, which can be used for the estimation of the ratio of fracture length and fracture height. It is found that the tracer behavior is dispersion dominated, which implies that values for dispersivity has to be known for the tracer test interpretation.

Extensive sensitivity analyses have indicated that the tracer test is only mildly sensitive to a large number of variables, which is beneficial for the purpose of hydraulic fracture diagnosis. It was also found that a conservative tracer is the best candidate for hydraulic fracture diagnosis using a single well test, since it has the largest diagnostic value when the tracer test is optimized.

Subjects of future research have been identified during this study. The potential of the use of tracers during the fracture treatment has been indicated and recommendations for future research to explore this potential are made. One possible way to do this would be to include a tracer adsorbed on the proppant or some equivalent chemical method for producing a tracer from the proppant.

The main conclusion is that tracers can be used for the diagnosis of hydraulic fractures with the ability to estimate the product of fracture length and fracture height. The accuracy of the estimation depends on the values for dispersivity used in the test interpretation, which therefore needs to be investigated further.

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