A New Environmentally Acceptable Technique for Determination of Fracture Height and Width
- Robert Ray McDaniel (Hexion) | Jerry Borges (Hexion Oilfield Technology Group) | Shubhanan S. Dakshindas (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 11-14 November, Anaheim, California, U.S.A.
- Publication Date
- Document Type
- Conference Paper
- 2007. Society of Petroleum Engineers
- 1.6 Drilling Operations, 4.1.5 Processing Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 3 Production and Well Operations, 2.5.1 Fracture design and containment, 2.2.2 Perforating, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control, 5.6.5 Tracers, 4.1.2 Separation and Treating, 5.2 Reservoir Fluid Dynamics, 1.14 Casing and Cementing
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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.
Ever since the first use of hydraulic fracturing, the oil industry has wanted information about the geometry of what wascreated.The desired geometry is most often referred to as propped length, width, and height. Early efforts focused on logging temperature profiles after a frac job. This technique was based on the "cooling effect?? that was created when the fracturing fluid was injected into the formation interval. Although this analysis gave indications of which parts of the interval had accepted fluid, it didnot give the desired information on the location of the proppant that had been pumped.
In more recent times, the use of radioactive tracers has grown in acceptance. Due to the inherent inaccessibility of the downhole environment, radioactive tracers have represented one of the few viable means for analyzing the placement and flow of various processes and materials¹. Radioactive tracers have been found to be useful in developing information in virtually all aspects of drilling, completing, and producing a well.
A particularly popular use of radioactive tracers is for the determination of propped fracture height. Fracture height measurement through the use of radioactive tracers and subsequent logging runs allow engineers to assess²:
- Post stimulation problems such as lower than expected production
- Design assumptions
- Possible modifications to future stimulation treatment designs
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