Conventional production logging tools proved to be efficient in vertical wells. When it comes to work in horizontal laterals production logging becomes much more complex. Common challenges are layered flow of reservoir fluid, deviation, wellbore accessibility, and stagnant zones along lateral. The tracer technology features a synthesis of a combination of marker-reporters made of a few quantum dots and a mixture of the polymer-based chemical composition. Quantum dots are nanocrystals produced using the process called colloidal synthesis. A single quantum dot is compounded of few hundred atoms and as small as 2-10 nanometer in diameter. Colloidal quantum dots irradiated with a laser emit light of different colors due to quantum confinement. The emittance of a particular specter of light can be detected using flow cytometry method. Several quantum dots joined together creates a unique and traceable marker-reporters element. There could be many unique tracer signatures (over 60). Utilization of quantum dots exclude any chance of misinterpretation while identifying tracers in samples of formation fluid. To achive superior accuracy in tracer identification we use software based on "machine learning". Qualitative and quantitative analysis of quantum dot marker-reporters in samples of formation fluid allows making informed conclusions about the performance of productive intervals of a horizontal well. Application of the technology showed the following benefits: the possibility of monitoring inflows for a long time, in contrast to a one-time logging operation; a significantly lower resource intensity and cost; confidence in conditions when the traditional downhole logging operations are complicated. Quantum dot tracer technology allows solving a number of problems, such as: post-fracturing inflow profile evaluation extended in time; assessment of each production interval in regard to water and oil production; optimization of technical solutions for well completions in the early stages of field development, such as number of ports; analysis of hydrocarbons extraction ratio; detailed information in the analysis of mutual influence of neighbouring wells in the oilfield. The application of the technology is particularly effective in the early diagnosis of water breakthrough, which allows enough time to choose the right technology for water shut off operation. Ultimately, this fact reflects in declining production rates and increasing incurred costs Major benefit is an ability to monitor production per zone at any time during five (5) years after deploying tracer-containing material downhole. Implementation of the technology is time efficient and does not require field equipment as well as crew for operation, which reflects on operating costs carried by customers.
Intelligent Inflow tracer technology can quantify zonal inflow contribution and identify the location of water breakthrough as its' primary monitoring capabilities. A novel chemical tracer system was permanently installed and successfully field tested in a horizontal oil producer in Saudi Arabia. These intelligent tracer systems allows the monitoring of the entire length of the production section, as early as the clean-up phase. They can also continuous production monitoring for up to ten years without the need for intervention. Some of the lesser known monitoring possibilities include inflow control valve actuation monitoring, packer integrity, multi-lateral and zonal inflow conformance. Understanding fluid influx profiles through permanent interventionless surveillance, has facilitated clean-up operations and improved long-term well performance, as presented in this paper. Unique oil and water soluble tracers are embedded in solid polymeric substrates and mounted on specialized carrier subs in each reservoir compartment separated by packers. When oil or water contacts the polymer substrates, the respective tracer is diffused out gradually with time. Produced fluid samples are collected at surface and analyzed for the presence of unique chemical tracers. The tracers can be measured down to parts per trillion (PPT), using advanced liquid chromatography coupled with a mass spectrometer. The presence and relative contribution of oil and/or water can then be determined for each downhole compartment in the reservoir. This inflow tracer technology was field tested in a 3000ft horizontal well, penetrating a carbonate reservoir. The openhole section was segmented into five compartments using packers which was also equipped with inflow control devices (ICD) integrated with sliding sleeves. Oil and water tracer carrier subs were placed in each of the five compartments. Initial surface sampling of first production showed water tracers from each of the five compartments, as expected with flowback of the completion brine. After clean-up the well produced 100% oil, and surface sampling indicated contribution from only the two heel compartments. The surface choke was opened to very high rate in an effort to clean-up the toe compartments. Subsequent surface sampling confirmed production from additional compartments many months after the cleanup but not from the toe. Periodic surface sampling has continued for nearly two years and will continue for the remaining tracer longevity. The tracers have been instrumental in pinpointing the location of water breakthrough and determining appropriate corrective intervention. In case of high water cut in any compartment, the offending segment(s) can be retarded by the closure of the sliding sleeve ICDs. The application of this wireless surveillance technology is a cost effective means for optimizing horizontal well performance, particularly in mature reservoirs and most appropriate for extended reach wells to overcome the limitations of PLTs and fiber optic monitoring solutions (Semikin et. Al, 2015).
At the present time, it has become progressively more common for countries around the world to use tracer's methods of production logging in horizontal wells. The utilization of tracers/markers doesn't require well intervention with Coiled Tubing or tractors in order to obtain qualitative and quantitative data for inflow of reservoir fluid per interval. Tracer/marker technologies is a quantum leap in production logging as it is potentially capable of producing ten (10) to twenty (20) times more downhole data in a period of several years. The knowledge of downhole production in dynamics of years helps in developing oil and gas fields, locating neighboring wells to be drilled, optimization of horizontal lateral length or even a number of fracturing stages per well. The principal difference between these technologies and traditional methods of well surveys (WS) is their ability to monitor the operation of ports or intervals in a well over a long period of time, with a significant reduction in resources involved, a reduction in costs and an enhanced production safety. However, the question remains whether the claimed specifications of tracer technologies correspond to the actual ones. Sometimes, the decision on the implementation of tracer PLT is made with weak quality assurance measures causing subsequent compromise of project results as a whole. The value of this article is the development of a methodology for a comprehensive assessment of the operability, reliability and accuracy of operation for various tracer technologies available in the market. Based on results of this research being conducted, the article suggests recommendations from producer companies that can be used as technical criteria when selecting a contractor for tracer studies.
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