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The Determination of Fracture Orientation Using a Directional Gamma Ray Tool, J.L. Taylor, III, et al, SPWLA 91-AA, June 1991.


The effectiveness of hydraulic fracturing operations is commonly evaluated by tagging the materials pumped downhole with one or more gamma-ray-emitting isotopes and subsequently logging the borehole with a gamma ray spectroscopy tool. Many times it is very desirable to also determine the orientation of the fracture planes. This paper describes a directional gamma ray tool which makes this possible.

The main tool component is a sodium iodide scintillation detector within a rotating tungsten shield containing a slotted aperture. A three-axis accelerometer is used to determine the direction of the gravity vector relative to the tool axis. The 1-11/16-inch-diameter toolstring consists of a gamma ray spectroscopy tool and a directional gamma ray tool. Optionally, a direction gyro survey tool may be attached.

The logging procedure is first to run the spectroscopy tool to determine the distribution of tracers. This allows depth intervals to be selected for stationary measurements and moving runs with the directional tool. Example logs from prototype tool field test illustrate the effectiveness of the directional gamma ray measurements. These results show that many gamma ray maxima exhibit significant azimuthal asymmetry. The interpretations of these asymmetries are discussed and compared with laboratory measurements.