NORM waste management in the oil and gas industry: the Syrian experience

This paper describes the Syrian experience with respect to Naturally Occurring Radioactive Materials (NORM) waste produced by the Syrian oil industry. Three main categories of NORM waste were identified. First, hard scales from decontamination of contaminated equipment and tubular that are considered to contain the highest levels of radium isotopes (Ra, Ra, Ra); this type of waste being currently stored in standard barrels in a controlled area. Second, sludge wastes containing low levels of radium isotopes were found with large amounts in each Syrian oilfield; plastic lined disposal pits were constructed in each area for temporary storage. However, disposal criteria for the above two categories of NORM waste are still under discussions. Third, contaminated soil with NORM as a result of uncontrolled disposal of production water was also considered as NORM waste. The Syrian criteria for disposal and clean up of this type of waste has been defined and the approved option by the Regulatory Office for disposal being the disposal mounds. Introduction Naturally Occurring Radioactive Materials (NORM) resulting from the Th and Useries can be concentrated and accumulated in tubing and surface equipment in the form of scale and sludge as a consequence of physical and chemical processes associated with the oil and gas industry. Radioactive wastes containing NORM are production water, which contains mainly radium isotopes, solid residues and production equipment. Solid residues consist of sludge and scales from tubing pipes and other production equipment. These radioactive wastes require treatment or disposal by appropriate • Email: [email protected] methods. Uncontrolled disposal of this type of waste could lead to environmental pollution and thus eventually to radiation exposure of members of the public. However, the largest generated volume of these wastes is produced water. Production water is usually separated from oil and disposed of by some means such as down an injection well or disposal well. Some companies may discharge this water into the environment for evaporation. Unlined lagoons or pits are usually built to collect this water and become highly contaminated with NORM. The presence of NORM in Syrian oilfields has been recognized since 1987 and the present paper describes the actions taken to manage NORM wastes in cooperation between the Atomic Energy Commission of Syria and the operating companies. In addition, the related regulatory controls associated with the disposal of such wastes are presented. NORM Measurement Methods 1. Determination of Ra isotopes in solid samples All soil and scale samples were dried in the oven for 48 hours at 105 C. The samples were then grinned and about 40g of each sample was filled in a special counting container and stored for two weeks for counting. Ra activities in the collected samples were then determined by measuring its gamma emitting daughters, Pb, Bi, Pb, Bi, Ac by gamma spectrometry using high resolution (1.85 keV at 1.33 MeV), high relative efficiency (26% and 80%) low background HpGe detectors. Sludge samples were stirred manually by a glass rod and filled in 0.5 liter plastic for counting. 2. Determination of Ra in production water samples Water samples were found to contain oil therefore, filtration through filter papers was required. Radioactivity analysis for determination of Ra in the production water was carried out by gamma spectrometry analysis. This was performed using two methods. First, the filtered sample (0.5 l) is stored in a plastic counting container, closed and counted after 2 weeks; this method being used when Ra concentration is expected to be high (higher than 3 Bq/l). The second method is to concentrate Ra from the sample (5-10 l) by precipitation with barium sulfate. The precipitate is then dissolved in 0.5 l 0.5 of 0.5 mol/l EDTA and the sample is placed in plastic container for counting. Each samples was counted for 24 hours using Ge (Li) Detector (Relative Efficiency 10%) and HpGe detector (Relative Efficiency 26.5%). 3. Determination of Po and Pb 0.2 gram of each solid sample was spiked with a known amount of Po (0.2 Bq) as a yield tracer. Each sample was then digested using a combination of mineral acids (nitric and hydrochloric acid) for at least 24h. When the solution was clear, the sample was then gently evaporated to near dryness. The residue was then dissolved in 100 ml of 0.5 mol/l hydrochloric acid. The solution was then heated to 80C and Po was spontaneously plated onto a rotating silver disc after reduction of iron with ascorbic acid. Alpha counting of Po (5.15 MeV) and Po (5.3 MeV) was done using an alpha spectrometer (Oasis, Oxford). The plating and counting were then repeated after 6 months of storage of the solution to measure the ingrowth of new Po from Pb and to calculate the Pb concentration in the original sample. The lower limit of detection of the method used was 0.4 Bq/ kg dry wt. NORM Waste Categories 1. Category I: Scale containing NORM waste Hard scales from decontamination of contaminated equipment and tubular using highpressure water systems or mechanical cleaning are considered to contain the highest levels of radium isotopes (Ra, Ra, Ra). Scales are currently stored in standard storage barrels in a controlled area; the number of barrels is increasing with time (around 93 barrels up till now). Table 1 shows some of scale samples analysis results; high levels of radium isotopes can be observed. The options for disposal of this type of waste are still under investigation; one of the most widely used is the re-injection into abundant wells. However, there are several internationally studied methods, some of which are land spreading, disposal mounds and others. On the other hand, big natural gas power stations have been built and operated for the last ten years. Maintenance operations of the gas stations produce tens of tons of scales containing radon daughters, Pb and Po with relatively high concentrations; only radon gas is usually present in natural gas. Some results of scales recovered from three big power stations are presented in Table 2. The common practice used to dispose of these materials is the disposal mounds where unlined pits being built near each power station. 2. Category II: Sludge containing NORM waste Sludge, oily sediment that is produced during cleaning operations of oil separators, storage tanks and other surface equipment, is considered as NORM waste. These wastes contain less activity than the hard scale; Table 3 shows some results of sludge samples analysis. Some oil companies have disposed of these waste into unlined pits; resulting in large areas being contaminated. Other companies implementing NORM management systems are currently using plastic lined disposal pits that are constructed in each area for temporary storage. However, regulatory approvals were given to oil companies to dispose of these wastes by mixing them with the NORM contaminated soil into a regulated disposal pits. Other permanent disposal methods are still under discussion. 3. Category III: NORM contaminated soil The third main NORM waste produced by the Syrian oil and gas industry is contaminated soil. Over 150,000 m of contaminated soil have been recognized. Radium-226 activity has reached a value as high as 100 Bq/g at the hot spots. Table 4 shows some average values at different sites. Contamination was found to be concentrated at the surface layer to a depth of 50 cm in most areas; few exemptions were observed where the contamination was found below 50 cm. Remediation work has been initiated where urgent regulatory controls were needed and implemented. The Syrian criteria for disposal and clean up of contaminated soil has been defined as follows: 1. Soil containing not more than 0.15 Bq/g of Ra does not need any treatment. 2. Soil having specific activity of Ra higher than 5.2 Bq/g need to be managed as radioactive waste. 3. Contaminated areas containing Ra with concentration between 0.15 Bq/g and 5.2 Bq/g need a special treatment on site to reduce the exposure to a value below