Abstract
For years, radioactive tracers have been used in combination with standard industry logging tools to gain valuable insight about the fracture height (near-wellbore vertical coverage) of proppant-packed fractures. The existing tracer technology has a number of safety and environmental issues that must be addressed when using this technology as part of a fracturing treatment. These issues, along with regulations concerning the transportation of radioactive materials, have impacted the application of this technology in international markets.
This paper will describe a new patent-pending technology that can generate valuable data on propped fracture height, as well as insight into propped fracture width. In this new technology, a non-radioactive tagging additive is incorporated into the resin coating of the proppant. This non-hazardous, environmentally safe, coated proppant can be transported and applied without any of the restrictions associated with radioactive tracers. Once the proppant is placed in the well, a gamma spectroscopy logging tool is used together with a fast neutron source to activate the tagging additive. The additive then becomes temporarily radioactive, emitting characteristic gamma rays that are visible to the logging tool's spectrometer.
The detected gamma ray response not only identifies the presence of the proppant, but in addition, the strength of the response is proportional to the amount of the additive/proppant that is present in the fracture, thereby providing insight on fracture width. Since the additive only responds when stimulated by the neutron source, the logging process can be completed free of any of the timing constraints associated with the half-life of presently used radioactive tracers and can be repeated as often as desired.
The additive used in this technology has been selected for a number of reasons, not the least of which is its very short half-life after being irradiated. By the time the logging process is complete and the well is ready to be placed in production, the additive will no longer emit a detectable level of radiation. This paper will describe this technology and its use in some detail. It will also present the results of initial field tests that utilized this new technology to determine aspects of propped fracture geometry.
