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