Tracer Technology and the Search for Oil
Posted at2019-05-07

      

                                  Tracer Technology and the Search for Oil


 A tracer tells you exactly what it sees, thereby optimizing the process.

 ——Tor Bjørnstad, Chief Scientist, Institute for Energy Technology, Kjeller, Norway

Ever since oil was first found off the shores of Norway in the 1970s, the country’s economy has seen tremendous growth. To maintain the efficiency of production for the long term, Norway has made extensive use of nuclear techniques. Nuclear tracers are used to help optimize oil production by mapping underwater oil fields. The benefits of nuclear tracer technology was one of the topics discussed during the recent IAEA Scientific Forum, Atoms in Industry: Radiation Technology for Development.

According to Tor Bjørnstad, Chief Scientist at the Institute for Energy Technology in Kjeller, Norway before the use of nuclear tracers scientists relied on seismic mapping, which delivered less precise data.

“A tracer tells you exactly what it sees, thereby optimizing the process,” Bjørnstad said. At present, the institute employs tracer technology in more than 30 different wells, while collecting samples from hundreds more.

Understanding the oil fields

Small quantities of radioactive material are mixed into the water or gas that is pumped down oil wells — around 5 ml for water-based tracers. Soil samples are then gathered from wells in the area, and if the tracer is picked up in multiple samples, it indicates that the wells are connected, drawing oil from the same reservoir (see box). Wells in which no radiotracer is found are separated by fault lines under the seabed. Understanding the extent of various oil fields is crucial in determining how to extract oil more economically.

Constructing a well costs upwards of 500 million kroner (US $62.5 million). Therefore, it has been a tremendous advantage to employ tracer technology, which is precise and causes minimal environmental impact, Bjørnstad explained.

Minimizing environmental impact

Meeting regulations and national safety standards, as well as international environmental standards, is a constant goal of the Institute for Energy Technology, Bjørnstad said. The sheer size of the oceans in comparison with the tiny amount of radioactive material used within tracers ensures that there is a negligible threat to the natural environment.

The Institute has helped many emerging oil producers to employ this method. The IAEA has also facilitated technology sharing both independently and alongside the Institute. The IAEA and the Institute help other countries obtain the necessary equipment to use the technique, and also set up courses, meetings and coordinated research projects that provide learning opportunities to Member States.

How chemical tracing works?

Polymer rods containing chemical tracers are typically installed in the completion in the different zones of the well. When the permanent tracers are contacted by target fluid, they will selectively release based on fluid contact.

The traditional method of interpretation for the inflow tracers is based on the quantification of transient flow, where the well is shut-in, a cloud of tracers is built up in the individual well zones, and then flushed-out when the well is opened. By analyzing the arrival pattern of tracers on the surface and tracer concentration decay during the start-up, it is possible to determine both qualitatively and quantitatively where production is coming from. Such data also provides important information with respect to well clean up, the efficiency of different well completions, economics in extended reach wells and well paths, and the identification of early problems such as water ingress.

However, with longer lifetime on systems--currently up to 10 yrs--a new use of the systems is opening up, with very low incremental cost to the operator. This is achieved through continuous monitoring of zonal well performance trends during production.

With the company’s well monitoring technology, small amounts of tracers are released continuously, and by analyzing samples taken from the well over a period of time (e.g. over two months with one sample taken every week) it is possible to correlate trends in zone-specific tracer concentration with trends and changes in production behaviour for the well. This can be related to oil/water/gas production rates, water cuts, gas-oil ratios, bottom hole/tubing head pressure/temperature and sand production.

Consequently, the tracers add a zonal resolution to the well production data for targeted well performance assessment and operational decisions. For instance, if the water cut suddenly increases, an increase in tracer signal from one of the zones will indicate from where and when the increased water comes from and what zone to keep under observation and consideration e.g. a targeted water shut-off operation.  Similarly, sudden drop in oil tracer signals can be used to identify targets for zone-specific stimulation to increase oil production from these zones. To expand the scope of fluid-specific information.




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