A New Environmentally Acceptable Technique for Determination of Propped Fracture Height and Width

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. Introduction 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 productionDesign assumptionsPossible modifications to future stimulation treatment designs

Review and Perspectives of Coated Proppant Technology

“…74 The method of logging is to directly detect the proppant in the fracture by adding radioactive chemicals to the proppant and then using logging equipment for detection. 75 However, this method is limited by the measurement radius of the logging tool, whose measurement range is usually only a few feet, while fractures can be hundreds of feet long, well beyond the measurement range of logging tools. 76 Seismic methods can detect fractures and faults but cannot detect whether fractures remain open.…”

Study on Interpretation Method of Multistage Fracture Tracer Flowback Curve in Tight Oil Reservoirs

“…By utilizing a neutron source and a gamma detector, it is possible to identify fracture proppants and determine fracture parameters by comparing the gamma-ray intensity emitted from activated materials in the proppants before and after fracturing. This technique allows for the identification of proppants used to support the fractures and the determination of fracture parameters . For non-Newtonian hydraulic fluids, once the fracture parameters governing their flow behavior are determined, the characteristics of underground fractures can be described through the interpretation of tracer flowback profiles using single-well tracer flowback analysis .…”

“…This technique allows for the identification of proppants used to support the fractures and the determination of fracture parameters. 21 For non-Newtonian hydraulic fluids, once the fracture parameters governing their flow behavior are determined, the characteristics of underground fractures can be described through the interpretation of tracer flowback profiles using single-well tracer flowback analysis. 22 Another method involves mixing tracer materials containing high thermal neutron capture cross-section elements with proppants and utilizing well logging techniques.…”