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Radioactivity based methods are widely used in petroleum engineering. They are used in many scales from the reservoir scale to the micro pore scale. The most common use of radioactivity in petroleum industry is well logging. To determine and evaluate the formation, gamma ray log is widely used in industry.
This log is sensitive to certain radioactive elements, such as uranium and thorium, and these radioactive elements are usually found in shale type formations. Another common use of radioactivity in petroleum industry is radioactive tracing.
Tracers are mainly used in reservoirs to detect and understand flow in a particular region. They are also used for the determination of injection patterns in reservoir, flow patterns in pipelines, leakage in pipelines, etc. Finally, it is not common to use radioactivity in core experiments in the laboratory, but it is possible. Saturation and permeability can be determined with this method in pore scale applications.
Radioactivity, also known as nuclear decay and radioactive decay, is the process by which an unstable atomic nucleus loses energy after emitting radiation.
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The emitted radiation can be caused by an alpha particle, a neutrino beta particle, or a beta particle having electron, and finally an internal transformation state, which is a result of gamma ray or electron. In general, a material with an unstable nuclei is considered a radioactive material [1].
The SI unit of radioactive activity is becquerel (Bq) , named after French scientist Henry Becquerel. 1 Bq is defined as one transformation or decay per second [2]. Ci or Curie was a former unit for radioactive activity, named after Nobel laureate Marie Curie.
A Ci is defined as the amount or mass of radium emanation in equilibrium with one gram of radium [3].
Devices with radioactive sources are used for a wide variety of useful applications. These include cancer treatment, blood irradiation for transplant patients, sterilization of medical equipment, non-destructive testing of structures, and petroleum exploration and production. In the oil industry, such resources are used in a variety of applications, such as radiography of platform and flow equipment, flow monitoring and down hole measurements for reserve estimation. Most common use of radioactive sources is logging formation parameters. Radioactive tracers, together with other materials in the hydraulic fracturing fluid, are sometimes used to determine the injection profile and the location of fractures generated by the hydraulic fracturing operation.
In 1896 Henri Becquerel used natural fluorescent minerals to examine the properties of x-rays which had been discovered by Wilhelm Roentgen in 1895. He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, believing that the uranium absorbed the sun’s energy and then emitted it as x-rays. This hypothesis was disproved on 26-27 February, when his experiment 'failed' because it was overcast in Paris. For some reason, Becquerel still decided to develop photographic plates. To his surprise, the images were strong and clear, proving that uranium emits radiation without an external source of energy, such as the sun. Becquerel had discovered radioactivity.
Becquerel used a device similar to the one shown below to show that the radiation he discovered could not be x-rays. X-rays are neutral and cannot be bent in a magnetic field. The new radiation is bent by the magnetic field so that the radiation must be charged and different from the x-rays [4].
Apparatus of Becquerel's Experiment
The term radioactivity was originally coined by Marie Curie, who, together with her husband Pierre, began to investigate the phenomenon recently discovered by Becquerel. The Curies extracted uranium from the ore and, to their surprise, found that the ore now had more activity than pure uranium. They concluded that the ore contained other radioactive elements. This led to the discovery of elements of polonium and radium. It was necessary to process tons of ores for four years to sufficiently isolate each element to determine its chemical properties.
Alpha particles interact more easily with matter because they carry more electrical charges, are larger, and move slower than beta and gamma particles. Beta particles are much less bulky and move faster, but are still electrically charged. One millimeter thick or several meters of aluminum sheet will stop these electrons and positrons. Since gamma rays do not carry electrical charges, they can penetrate large distances from materials before interacting - several centimeters of lead or one meter of concrete are needed to stop most gamma rays [5].
When the two nuclei have the same atomic number but different atomic weight or mass numbers, they are said to be isotopes. Isotopes have the same chemical properties, but have different physical properties. For example, carbon (C) has two isotopes, 6C14 and 6C12. Both have the same atomic number but have a different number of neutrons. It has two extra neutrons, undergoing radioactive and radioactive degradation. Radioactive isotopes of carbon have been used to develop a carbon dating tool that makes it possible to date various residues.
Half-life is the time required for the degradation of the half-amount of radioactive element. For example, C14 has a half-life of 5730 years. So, if you get 1 gm C14, half of it will deteriorate in 5730 years. The following figure shows the half-life of some elements [6].
Radioactive Decay Types
Alpha Decay: The nucleus emits a Helium nucleus (called an Alpha Particle) and is converted to another nucleus whose atomic number is reduced by 2 and atomic weight is reduced by 4.
The measurement versus depth or time, or both, of one or more physical quantities in or around a well is called well logging. The term comes from the word 'log' used in the sense of a record or a note. Wireline logs are taken downhole, transmitted through a wireline to surface and recorded there. Measurements-while-drilling (MWD) and logging while drilling (LWD) logs are also taken downhole. Different types of well logs are available and used in petroleum sector.
Resistivity Log
Borehole Imaging
Density Log
Neutron Porosity Log
Sonic Log
Gamma Ray Log
Self/spontaneous Log
Caliper Log
Nuclear Magnetic Resonance
Spectral Log
Gamma ray logging is a method for measuring naturally occurring gamma radiation to characterize rock or sediment in a borehole or drill hole. It is a wireline logging method used for mining, mineral exploration, formation assessment in water, oil and gas well drilling and other related purposes. Different rock types emit different amounts and different natural gamma radiation spectra. Specifically, shales emit more gamma than other sedimentary rocks such as sandstone, gypsum, salt, coal, dolomite or limestone, because radioactive potassium is a common component in the clay content and causes the cation exchange capacity of the clay to adsorb uranium and thorium.
This difference in radioactivity between rocks and sandstones / carbonate rocks allows the gamma-ray tool to distinguish between stones and non-stones. However, they cannot distinguish between carbonates and sandstone because both have similar deviations on the gamma ray stump. Therefore, it cannot be said that gamma ray logs make good lithological logs themselves, but in practice, gamma ray logs are compared side-by-side with stratigraphic logs[8]. A sample gamma ray log can be seen in the figure below.
Three elements and their decay chains are responsible for the radiation emitted by rock: potassium, thorium and uranium. Shales usually contain potassium as part of their clay content and tend to adsorb uranium and thorium. A common gamma ray mass records total radiation and cannot distinguish between radioactive elements when recording a spectral gamma ray file.
The advantage of gamma log over some other types of well log is that the bore holes in the pulley pass through steel and cement walls. Although concrete and steel absorb some of the gamma radiation, they move sufficiently through steel and cement for qualitative determinations.
Spectral recording is a technique of measuring the spectrum or number and energy of gamma rays emitted by the natural radioactivity of rock formation. There are three main sources of natural radioactivity in the world:
Each of these radioactive isotopes emits gamma rays having a characteristic energy level measured in MeV. The amount and energy of these gamma rays can be measured with a scintometer. A mass of the spectroscopic response to natural gamma-ray radiation is generally presented as a total gamma-ray file indicating the weight fraction of potassium (%), thorium (ppm) and uranium (ppm). The primary standards for weight fractions are geological formations with known amounts of the three isotopes [10]. Natural gamma ray spectroscopy recordings were routinely used, although they were studied from the early 1950s to the 1950s.
Characteristic gamma ray line associated with each radioactive component:
Another example of the use of spectral gamma ray logs is to identify specific clay types such as kaolinite or illite. This may be useful for interpreting the deposition medium as kaolinite can form in tropical soils by forming potassium leaching from feldspar; and low potassium readings may therefore indicate the presence of one or more paleosols [10]. The identification of specific clay minerals is also useful for calculating the effective porosity of the reservoir rock. The following figure shows an example of a spectral gamma ray log.
Tracers A component of a production logger that carries a radioactive solution that can be selectively released into a flow stream. When the radioactive solution is released into an injected fluid, the movement of the mixture can be monitored by gamma ray detectors inside the instrument. Radioactive tracers are used in injection wells rather than production wells to prevent surface radioactive contamination. The main applications of radioactive tracers are to create flow profiles in injection wells, to detect fluid movements behind the pipe, and to find fluid movement between leaking packers and wells. According to a 1995 study, radioactive tracers were used more than 15% of simulated wells worldwide to check whether the operation was successful [12].
Since 2003 Antimony-124, argon-41, cobalt-60, iodine-131, iridium-192, lanthanum-140, manganese-56, scandium-46, sodium-24, silver-110m, technetium-99m isotopes and xenon -133 was mostly used by the oil and gas industry, because they are easily recognized and measured. Brom-82, Carbon-14, hydrogen-3, iodine-125 are also used [13]. The use of these radioactive tracers is strictly controlled. Each district has its own regulations on its use. In general, however, it is recommended that the radiotracer have readily detectable radiation, appropriate chemical properties, and a level of half-life and toxicity to minimize initial and residual contamination. An example table summarizing the use of radioactive tracer can be seen in the following figure.
Radioactive tracers are used in a wide variety of applications to mark the movement of oil stocks in various transport and refining phases. Interfaces between different stocks in a pipeline are marked with radioactive in routine distribution operations by a pipeline company. Flow rates in refining units are measured and monitored by radioactive tracers injected into the stream. Flow patterns in complex equipment can also be monitored. Leakage can be detected and sometimes measured.
A more recent application to pipelines is to mark the product interface. When different products are pumped repeatedly along the same pipeline, it is necessary to distinguish between them at the final point. For example, when a pipeline carries different API oil that belongs to different companies. If an oil-soluble radioactive tracer is injected into the stream at the point where the interface occurs at the pumping station, it can be detected by Geiger meters connected to the pipe when it reaches the terminal station. This requires a radioactive element with gamma rays of sufficient energy to penetrate the pipe wall and a half-life to withstand the end of the journey [14].
Laboratory studies for the flow of fluid fluid through porous media have always been used in petroleum engineering to obtain the most appropriate methods for oil reservoirs. Flow behavior studies in porous media using neutron radiation. Liquid saturation in the cores and sand packs was determined by irradiation with fast neutrons from a radium-beryllium source. Because fast neutrons have been slowed down much more than any existing element with hydrogen. The density of the slow neutrons provided an index of hydrogen concentrations, and hence total liquid saturation.
Basic experiments using gamma-ray emitting radioactive tracers to demonstrate fluid saturation were reported in 1917 by Russell, Morgan and Muscat. The radioactive tracer method requires minimal equipment, only the trace concentration of radioactivity is needed and can be obtained for good definition point measurements. Russell and Muskat used radioactive vanadium in the water phase to determine the mobility of interstitial water in the flooding processes. Such a connection water has been found to be highly mobile [15].
Radioactivity Applications in Turkey Since there is an active oil and gas industry in Turkey, it is possible to say that the application of radioactivity is available in Turkey. Gamma ray logging is used in Turkey and is still available Turkish petroleum and Mineral Research & Exploration General Directorate are the national companies that capable of taking gamma ray logs. These two takes gamma logs for both their own fields and some companies like Perenco, Transatlantic, Zorlu energy etc.
Some other companies like Güney Yıldızı Petrol has their own logging unit an uses this unit for their field and in addition to that they work as a service company and takes gamma ray logs for pre-mentioned companies. The third type of companies are direct service companies. Schlumberger, Baker Hughes and Viking and Weatherford works in the Turkish oil and gas market and offers gamma ray applications to those who has not possess this facility. There are different prices for gamma ray logging for different conditions depending on the well dynamics, so it is not possible to give a specific price for this application.
On the other hand, tracing the fluid while it flows through the porous media is not common and probably is not available in Turkey's petroleum industry.
Applications based on radioactivity are getting more and more often used in many different industries as the time passes in the era of technology and science. The oil and gas industry is one of them. The most common technologies based on radioactivity are gamma ray logging and radioactive tracers. The basic principle behind gamma ray logging, when and why it is used, and gamma ray logging applications are explained in detail in this paper.
Usage of this technology in Turkey, which companies have gamma ray logging tools and have the operations are performed is also explained. In addition to gamma ray logging, tracer applications are also analyzed in this paper. Again, basic principles related to the use of radioactive tracer are given. In conclusion, when, why and how to use some of the radioactive applications are mentioned in this paper.
Radioactivity in Petroleum Engineering: From Well Logging to Tracer Applications. (2024, Feb 22). Retrieved from https://studymoose.com/document/radioactivity-in-petroleum-engineering-from-well-logging-to-tracer-applications
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