NATURALLY OCCURRING RADIOACTIVE MATERIALS IN MALAYSIAN OIL AND GAS INDUSTRIES

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1 NATURALLY OCCURRING RADIOACTIVE MATERIALS IN MALAYSIAN OIL AND GAS INDUSTRIES Y. M. Amin, Y. Abdulla and H. W. Nik* Physics Department University of Malaya Kuala Lumpur. *Asia Lab(Mal) Sdn Bhd Block B-5-7 Menara Uncang Emas, 85 Jalan Loke Yew Kuala Lumpur ABSTRACT Naturally occurring radioactive materials (NORM) were found to be more concentrated in sludge and scales from oil and gas facilities and hence they are also referred as technically enhanced NORM or TENORM. This paper will be discussing the origin and types of radioactive materials and also the specific locations of scales and sludge in tubular, vessels, valves and other process equipment. Some results of radiation level and radionuclide concentrations in oil and gas facilities in West and East Malaysia will also be presented. 1. INTRODUCTION Naturally occurring radioactive materials (NORM) is broadly distributed throughout the environment. It is present on earth because of their long half-lives or being constantly produced by natural processes such as the interactions of cosmic rays with atmosphere and the decay products of long-lives radionuclides. Many of the rocks of the formation strata where oil and gas reservoirs are found contain NORM mostly uranium-238, thorium-232 and there decay products as shown in Table 1a and 1b respectively. Potassium-40 and uranium-235 are also detected but is usually ignored on the ground that it has no radiological significant. The oil and gas reservoirs also contain various quantities of water. This formation water is usually rich in chloride and will dissolve minerals from the strata including the NORM and their decay products. Chemical incompatibilities between the formation water and seawater and a sudden change in pressure and temperature, can lead to a favorable condition for precipitation of simple and complex salts. The salts are calcium carbonates, calcium sulfate, barium sulfate and strontium sulfate. The chemistry of these sulfates is similar to that of radium which can co-precipitates readily to form inorganic sulfates. These sulfates form part of the scale, which is now contaminated with NORM. Radium salts have also being observed to be transported throughout the system and the concentration maybe- enhanced in sludge due to adsorption onto clay silts present in the sludge. A further mode of enhancement is due to the migration of dissolved radon in

2 produced water and sludge. Radon progeny in storage tanks, which contain sludge can result in the activity to increase in the sludge itself and may also plate-out on the tanks wall. The increase in the activity due to man intervention resulted in NORM to be called technically enhanced naturally occurring radioactive materials (TENORM). Symbol Radiation Half-life U x 10 9 years Ra x 10 3 years Rn days Po-218 and 3.05 min Pb min Bi-214 and 19.7 min Po x 10 s (a) Symbol Radiation Half-life Th x years Ra years Ac hours Ra days Rn s P s Pb hours and Bi min and Po x 10-7 s Tl min (b) Table 1(a) and (b) The prominent decay series of uranium-238 and thorium-232 respectively. 2. LOCATION OF TENORM IN OIL AND GAS PRODUCTION UNIT The deposition of scales containing radium isotopes are high in items where there are changes in pressure and temperatures such as production tubes, valves, separator vessels and oily water treatment unit. The scale can adheres to surfaces and can also be dispersed in sludge, particularly in crude oil storage vessels. Figure 1(a) and (b) show the possible locations of TENORM in offshore and inshore oil production unit respectively. The deposit consists of white/brownish brittle solid of density approximately 4.0 g/cm 3 which adheres tenaciously to the substrate on which its has formed. The deposits are to all intents and purposes inert and impervious to the effects of all common solvents, concentrated acids and alkalis.

3 Figure 1(a) and (b) Simplified offshore and inshore oil production unit showing the possible location of TENORM respectively. 3. RADIOLOGICAL MONITORING IN OIL AND GAS FACILITIES RESULTS AND DISCUSSIONS Monitoring of radiation level and the concentration of various nuclides such as radium- 226 and radon gas is carried out in accordance to the guidelines produced by Atomic Energy Licensing Board (AELB)(1). Two types of monitoring namely specific and routine monitoring are carried out. 3.1 Specific Monitoring This type of monitoring is carried out during inspection and maintenance of equipment suspected of being contaminated with TENORM such as large vessels, tubular and storage tanks. Before any work begin, in situ measurement of radiation level is carried out using a calibrated survey meter. Table 2 shows a typical in situ mean external radiation level for onshore and offshore in Peninsular Malaysia. As required by the guidelines, surface contamination, concentration of Ra-226 and Ac-228 in air, liquid and scale are also carried. In these cases, samples are collected

4 Location Range Ext. Radiation level (µsv/h) Mean Ext. Radiation Level (µsv/h) 0.22± ±0.01 Table 2(a) Summary of specific in-situ external radiation level for Peninsular Malaysia and analyzed in the laboratory. In situ radon concentration is also measured. Table 2(b) to 2(d) summarized typical results for the above parameters for Peninsular and East Malaysia respectively. Location Range Alpha Surface Contamination (Bq/cm 2 ) ND* ND-0.016* Mean Alpha Surface Contamination (Bq/cm 2 ) ND* 0.011± ±0.002* 0.004±0.001 Table 2(b) Summary of specific in-situ alpha surface contamination for Peninsular* and East Malaysia. ND= not detected Location Radium-226 (Bq/m 3 ) Actinium-228 (Bq/m 3 ) MDA MDA - MDA MDA - Table 2(c) Summary of specific long-lived air-borne radio-nuclides in Peninsular Malaysia. MDA= minimum detectable activity Location Radon-222 (WL) Radon-220 (WL) LLD LLD LLD LLD Table 2(d) Summary of specific radon and thoron concentration in East Malaysia. 3.2 Routine Monitoring Long term in situ monitoring near the vessels surface, storage tanks, and sludge treatment and storage areas is carried out using thermoluminescence dosimeters (TLD) usually of the type TLD-100H. Table 3 shows typical results for oil terminals in East Malaysia. The average annual level is around 1.2 msv, which is slightly higher than the background level in Miri, Sarawak (2). Other parameters as in

5 Location External Radiation Level, TLD (msv/month) Mean Ext. Radiation Level (msv/month) ± ± 0.02 Table 3 A routine long term measurement using TLD for East Malaysia. Radium 226 (Bq/g) Actinium- 228 (Bq/g) ND ND Table 4 Activity of sludge during routine measurements in East Malaysia oil facilities. specific monitoring are also measured but at an interval of 6 to 12 months at each location. Table 4 listed typical results for routine monitoring in oil facilities in East Malaysia. For comparison, the background of various places in Miri, Sarawak is listed in Table 5. Sampling Location Tanjung Lubang Playground Bulatan Park Pengkalan Lutong Old General Hospital Activity (Bq/g) Radium-226 Actinium Table 5 Background concentration of radium-226 and actinium-226 in several locations in Miri, Sarawak. The mean activity of the sludge is a factor of ten higher than the activity in soil around Miri, Sarawak. Therefore, a continuous radiological assessment of oil and gas facilities is needed. Certainly the sludge could not be disposed without a proper radiological impact assessment (RIA) carried out and approved by the appropriate authorities. CONCLUSION All the oil and gas facilities in Malaysia produced TENORM. However the activity is slightly above the background values and varies from location to location as well as time of monitoring or sampling. 4. REFERENCES 1. Guidelines on radiological monitoring for oil and gas facilities operators associated with TENORM, LEM/TEK/30 SEM. 2, AELB. 2. Principles of Radiation Protection, Y.M.Amin and D.A.Bradley, University of Malaya Press (2001)