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| Fig. 1: South-East Kuwait Oil Field. (Courtesy of NASA. Source: Wikimedia Commons) |
The state of Kuwait, known for its colossal oil reserves and production, officially reported its first radioactive oil by-product in 2011. This case and the majority (>98%) of following radioactive cases, are located in Kuwait's northern oilfields. The country's initial response was abandonment of all radioactive wells, leading to oil deferment of 30-40 thousand barrels per day. [1] In 2014, Kuwait's national oil operator secured a contract facilitating safe and cost-effective procedures to manage, and store radioactive waste. This agreement, active to date, is carried by a specialised radioactive waste handling vendor to ensure minimum oil deferment while maintaining employees' welfare.
In 2002, the International Atomic Energy Agency (IAEA) conducted a study on the radiological conditions in areas of Kuwait with residues of Depleted Uranium (DU), since DU munitions were extensively used in the 1991 Gulf war. [2] The estimated annual radiation doses that could arise in the areas where residues do exist are of the order of a few microsieverts: 29 µSv in Al-Abdali (northern-most point of Kuwait's oilfields), 7.7 µSv few kilometres south of Kuwait's northern oilfields, and 13 µSv in its western oilfields. These all are well below the annual doses received by the population of Kuwait from natural sources of radiation in the environment of ~ 2.4 mSv (0.27 µSv/hr) and far below the action level of 10 mSv suggested by the International Commission on Radiological Protection (ICRP) as a criterion to establish whether remedial actions are necessary. [2] It is worth noting that Sievert (Sv) is an "effective dose" unit used to quantify the combined amount of radiation absorbed by human cells and the medical effects of that type of radiation on one's health. [2] The study concluded that DU does not impose any radiological hazard on the population of Kuwait, nor it overshadows the background radiation by natural sources in the region. However, it is worth noting that DU and its immediate decay products emit alpha (α), beta (β) particles, and a small amount of gamma (γ) radiation; yet, there was an eminent focus in the study on gamma (γ) exposure by Kuwaitis. The study also suggests that ingestion of alpha (α) and beta (β) particles is negligible due the confinement of DU emanation shells to unoccupied deserted areas. [5]
The first study on natural radioactivity measurements in Kuwait's oilfields was led in 2008 by Kuwait University. It was motivated in part by concerns about naturally occurring radionuclides in the Gulf region attributed to oil production. [3] The most important naturally occurring radionuclides in Kuwait's source rocks (limestone, sandstone, and shale) are Th-232, K-40 and Ra-226 from the uranium-radium series isotopes. [3] Gamma (γ)-ray measurements of each isotope's activity concentration have been performed, and it has been concluded that Kuwait's average radioactivity from both the reservoirs (oil/formation water) and accumulated sludge are relatively low compared to world wide averages. [3] The amount of a given radionuclide in a particular material is normally expressed in terms of "activity", which is the rate at which nuclear transformations occur; the SI unit of activity is the becquerel (Bq). [2] In the case of Kuwait University's study, the activity is measured in Bq per kilogram of soil and formation water. Soil samples were collected from un-weathered surfaces and from 30-40 cm depths, whereas water samples were collected from produced water of the designated layer itself. [3] Field-specific comparisons indicated that both Th-232 and Ra-226 concentrations in formation water are much higher in the northern oil fields, although still lower than world-wide averages. [3] Radioactivity, however, in North Kuwait field's soils (Th-232: 27.9 Bq/kg) is higher than the world-wide value (Th-232: 25 Bq/kg) and also higher than local background values (Th-232: 14.2 Bq/kg). [3] This study focused solely on oil, sludge, and formation water samples, omitting any facilities, surface, and subsurface components.
Almost all (~99%) reported radioactive wells in north Kuwait are equipped with Electrical Submersible Pumps (ESPs). Oilfield equipment can contain radioactive scale and scale-bearing sludge, both of which form as coatings or sediments. [4] It has been confirmed that radioactive deposits form when radioactive isotopes precipitate with sulfate based scales caused by mixing of injected seawater with formation water. Deposition can be accelerated by other variables such temperature, pressure, salinity, pH, turbulence, nucleation, and kinetics of precipitation. [4]
In the early 2000s, north Kuwait embarked a large scale water injection project to replenish pressure support in all of its depletion-drive reservoirs. Water injection is not confined to north Kuwait, and is largely implemented in Kuwait's south-eastern fields (Fig. 1). However no/negligible cases of radioactivity have been reported to date in the latter. Moreover, a considerable fraction of the wells in north Kuwait are not under any water injection scheme yet are radioactive. Average gamma (γ) background readings in Kuwait's northern oilfields are ~ 0.085 µSv/hr, with ESP components' readings ranging from (~ 0.03 to 0.330 µSv/hr). Although the majority of gamma (γ) measured values are lower by one order of magnitude than the international standard for oil and gas operators (~0.5 µSv/hr), however, almost all radioactive cases have recorded alpha (α) and / or beta (β) readings to be exceeding five-times the background values which are ranging from ~ 0.77 to 0.85 counts per second (CPS). This indicates that alpha (α) and / or beta (β) particles are the dominant contributors to radioactivity in Kuwait. The source could be either artificial (DU), and / or natural (Th-232 (α emitter), K-40 (β & γ emitter), and Ra-226 (α & γ emitter); no confirming analysis has been performed yet.
ESPs were first installed in north Kuwait in the early 1980s. Their installation at north Kuwait's depletion drive reservoirs only started in 2008. From 2004 onwards, radioactive measurements were mandated while testing ESPs pre- and post- installation. Seven years later, the first radioactive ESP case from a depletion drive layer was reported. It exhibited more than twice the background radioactive reading of alpha (α) and / or beta (β) particles (this was the original threshold criterion).
Water injection and ESPs are probably not the sole cause of radioactive by-products, and there must be additional factors. Pump setting depth, for example is one differentiator between north and south-east Kuwait oilfields. This, however, does not explain the three-year lag between seawater injection and the first radioactive detected case. The radioactive factorasition matrix remains a field worthy of in-depth investigation, propelled by the detrimental / acute effects of alpha (α) and / or beta (β) particles ingestion.
Kuwait's national oil operator shifted its focus from the radioactivity's root-cause to investigating more pro-active approaches to solve the problem. As with the current readiness of radioactive event and waste management, the country's main concern is storage and handling of surface radioactive waste. Accordingly, several field trials took place aimed at reducing/eliminating surface radioactive waste, starting with injecting and soaking of downhole ESP strings with de-scaling chemicals. Formation stimulation was also found to have a positive impact on reducing the reoccurrence of radioactivity. Immobilising radioactive ions through use of metal legends under controlled pH environments was also recently studied. [5] Even though these approaches succeeded, they were costly and thus impractical to sustain. The last method was also not put into field trial due the requirement of a low pH, which jeopardises the integrity of the downhole well structure. Kuwait and most oil operators are behind when it comes to understanding and handling radioactive waste and by-products. To date, the matter is treated reactively with low-efficiency schemes. Once comprehensive understanding of radioactivity causes is attained, proactive solutions then can be proposed and implemented.
© Nora AlMaqsseed. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] N. Saleh, H. Chethri, and M. Al-Mutawa, "Turning Threat into Opportunity: NORM Management Helps to Recoup the Deferred Production From North Kuwait," SPE Kuwait Oil and Gas Show and Conference, Mishref, Kuwait, One Petro SPE-198117-MS, 13 Oct 19.
[2] "Radiological Conditions in Areas of Kuwait with Residues of Depleted Uranium," International Atomic Energy Agency, STI/PUB/1164, 2003
[3] F. H. Abdullah, H.R. Saad, and A.R. Farhan, "An Investigation of Naturally Occurring Radioactive Materials (NORM) in Oil Fields and Oil Lakes in Kuwait," SPE Int. Conf. on Health, Safety, and Environment in Oil and Gas Exploration and Production, Nice, France, One Petro SPE-111562-MS, 15 Apr 08.
[4] R. A. Zielinski and J. K. Otton, "Naturally Occurring Radioactive Materials (NORM) in Produced Water and Oil-Field Equipment An Issue for the Energy Industry," U.S. Geological Survey, FS-142-99, September 1999.
[5] X. Du, et al., "Reduction of Uranium(VI) by Soluble Iron(II) Conforms with Thermodynamic Predictions," Environ. Sci. Technol. 45, 4718 (2011).
