Iraqi Geological

Abstract


Introduction
The East Baghdad oilfield is one of the important oilfields in Iraq.Tell now 97 oil wells were drilled in East Baghdad oilfield.The industry produces approximately 10,000 barrels of oil per day from a total of 40 wells.The EBS oilfield is believed to have a production potential of 40,0005 barrels per day.It is known that pumping oil from the reservoir to the surface in oil production will bring with it radium-226 and its daughters, while uranium will remain in the reservoir rocks (IAEA, 2003;NRPA, 2004;OPG, 2008).Likewise, thorium and its daughters and potassium will move with the oil and associated water to the surface when pumping crude oil.This may cause the accumulation of these nuclides in the pipes or leak out through the connections of the pipes or the valves, Whether in other stages or activities of oil and gas production within the oil field.Naturally occurring radionuclides or what is called NORM, their concentrations may increase significantly during the separation of oil from water.For example, the concentration of radium increases in the sludge and the final residues, as it moves with the oil from the oil reservoir, while uranium-238 (the parent nuclide) remains in the reservoir and does not move to the surface (IAEA, 2003) IAEA has published many technical series and documents regarding this topic (IAEA, 2003;IAEA, 2004;IAEA, 2005;IAEA,2008;IAEA, 2010).Numerous countries have undertaken investigations into NORMs.Othman and Al-Masri (2002) addressed the characterization of the oilfield sites that are NORM-contaminated in Syria.The data employed to conduct a quantitative risk assessment and explore potential approaches for the ultimate disposal of the contaminated soil.Elegba and Funtua (2004) conducted a study on the assessment of (NORM) in Nigeria's oil and gas production facilities.They found elevated concentrations in some stages of oil production.Al-Farsi (2008) examined NORMs in petroleum production in Oman, concluding natural radionuclide concentrations exceeded ambient soil levels and displayed significant variation.Clerckx (2010) conducted research on NORM oil and gas industry in Belgian.Garcia (2011) identified enhancements in NORM waste management processes within Norwegian oil and gas industry.Attallah et al., (2012) discussed the environmental radiation of Technical enhanced NORM waste from Egypt's oil industry, emphasizing waste's origin and characteristics.Concentrations of 226Ra exceeding international regulations required risk reduction for indoor radon and direct gamma radiation exposure.Benedict (2012) studied NORM in soil samples from radioactivity-rich regions near an oil field in Qatar.In Iraq, many researches published regarding the NORM in oilfields.Al-Talib, (2015) investigated the (NORM) and (TENORM) on oil fields in Kirkuk area.High radioactivity was measured in some locations within the study area due to the contamination with NORM.Nafae (2015) explored of NORM-contaminated soil through leaching within various solvents, focusing on reuse.The study identified multiple sites contaminated with Ra-226.Ali and Ibraheem (2017) conducted a study on the radiological risk associated with NORM in the oil and gas industry within the northern part of the East Baghdad Oilfield.They found that, from a radiological perspective, the majority of locations were considered clean during the period of their research.However, certain sites required periodic waste management due to contamination, specifically in areas related to water treatment, well disposal, and bit burning.In a separate study by Ibraheem (2017) focusing on the radiological impact of NORM in the East Baghdad Oilfield, it was concluded that most sites demonstrated background-level radioactivity.Nevertheless, a few locations had experienced contamination from waste generated during oil production.Ali et al. (2017) conducted a study on the radiological assessment of NORM originating from oil and gas production processing in Rumaila oil field.The results show that some locations within the south degassing station (SDS) are contaminated with NORM.The dehydrator and desalter stages were identified as the most contaminated areas compared to other locations within the oil and gas production processing stages in the SDS.Hussein, (2017) studied the radioactivity of NORM in Rumaila oilfield, his study included assessment of radiological effect of NORM in two sites of oil and gas production.Some locations of the two sites have radioactivity above the level recommended by IAEA and other relevant agencies.The objective of the study is to assess NORM and its radioactive impact on the southern part of the East Baghdad oil field.

Study Area
EBS is located east of Baghdad, the site spans a length of 60 kilometers and a width of 12 kilometers (Fig. 1).Situated within the EBS field concession, it encompasses an expanse of 822 square kilometers.Geographically, the East Baghdad oil field is divided into six regions, proceeding from northwest to southeast: North Extension, Urban, South 2, Al-Taji, Al-Rashdiya, and South 1 areas.The southern part of the East Baghdad oil field comprises both the South 2 and South 1 areas.(MODC, official website).

Materials and Methods
Within this study, a total of ten samples were gathered from various points along the oil production line within the EBS facility.The samples represent soil, sludge, crude oil and waste oil and water obtained from the EBS facility.These samples present the stages of oil production from the first to the final stages (Fig. 2 and Table 1).These samples were collected and sealed within a plastic bag of 3kg within its information (sample number, Coordinates, date, and type).The sample presents sludge (SL), soil (SE), crude oil (CO), waste oil (WO), wastewater (WW), and evaporates water (EW).The soil and sludge samples took at a depth down 3 cm from the surface and covering an area of 1m (IAEA, 1989).The sampling was done by using a small shovel.There was some difference in the number of samples due to the soil density.A global positioning system (GPS) with accuracy (± 10 feet) was used to determine the coordinates of the samples.The samples were kept in a couple of bags (nylon bags) for preventing the soil from leaking or losing any information obtained from them.This data encompassed details such as sample ID, date, and location.Subsequently, the collected samples underwent preparation in laboratories before being forwarded to the Radiation Protection Center (RPC) under the Ministry of Environment for analysis of radioactivity.

Samples Preparing
The samples (surface soil, sludge) were heated in electric oven with a temperature that is fixed of (105 ºC) for a sufficient period of time to make sure they were dry.The next step is removing any bulks of pebbles by using a sieve of 1mm.The last step presents crushing and powdering all of the samples and preparing them for the radioactivity measurements.Each sample undergoes meticulous homogenization.A quantity of 0.5-1 kg is extracted from the samples and stored in a tightly sealed Marinelli beaker for a period of 25 days.This duration allows for the establishment of equilibrium between radon and its progeny (IAEA, 1989).

Radioactivity Measuring
For analyzing NORM in samples, a HPGe (High-Purity Germanium) Gamma spectrometry system was employed.Concentrations of NORM nuclides that were measured in the samples, expressed in units of Bq/kg.To calculate specific activities, gamma-ray photo peaks at multiple activities were averaged for 226Ra, specific activity determination utilized gamma-ray lines at 180.5 keV or at 295.2 keV and 351.9 keV from 214Pb, along with 609.3 keV and 1764.5 keV from 214Bi.For 232Th, gamma-ray lines of 338.4 keV and 911.2 keV from 228Ac, 727.3 keV from 212Bi, and 583.2 keV and 2614.5 keV from 208Tl were employed.Direct measurement of 40K's specific activity was done using its gamma-ray line at 1460.8 keV.To calibrate energy and efficiency, a standard multi-energy source provided by the American Canberra Company was used.The Marinelli was utilized for both sample radioactivity measurement and calibration source.All the measurements were conducted by laboratories at the Radiation Protection Center (RPC).

Radioactivity of NORMs Inside ESB
The NORM activities within all samples from the EBS facility are summarized in Table-1.The table indicates that The highest Radium-226 (Ra-226) activity, reaching 153.1 Bq/kg, and was found in sample (SL2) taken from the second stage of the initial separator (Fig. 2) prior to its transfer to separator 2. Conversely, the lowest activity of 24.5 Bq/kg was recorded in wastewater and water treatment samples.
The highest Thorium-232 (Th-232) activity, at 83.7 Bq/kg, was observed in the sludge sample (SL2), while the least activity of 3 Bq/kg was detected within treatment water.Regarding Potassium-40 (K-40), the maximum value of 1264.2Bq/kg was found in the 1st separator sample, while the lowest activity of 15 Bq/kg was recorded in waste oil.
The radioactivity distribution of Ra-226, Th-232, and K-40, and total measured exposure dose rates shown in Figs. 3, 4, 5 and 6.In the 1st separator at the SL2 location, the concentration of Thorium-232 (Th-232) was observed to be approximately twice the worldwide average.Fig. 5 illustrates that roughly 70% of the sampled locations exhibited Potassium-40 (K-40) concentrations surpassing the global average for K-40 in soil, set at 412 Bq/kg.Additionally, around 10% of the locations displayed K-40 concentrations ranging from 1210 to 1610 Bq/kg.The total exposure rates measured across all EBS locations exceeded the worldwide average value of 0.0604 µSv/h (equivalent to 58 nGy/h) (Fig. 6).The total exposure dose rates in the EBS area ranged from 0.09 to 0.13 µSv/h, corresponding to 63-91 nGy/h, with an average of 74.9 ± 10 nGy/h.This average value surpasses the worldwide average outdoor dose rate of 58 nGy/h reported by UNSCEAR ( 2008).The highest value was recorded near the waste pit (sample SC6) where sludge had been deposited.This outcome is expected due to the high concentration of radium-226 present in this area.

Estimation of Hazard Indices
In the world-wide multiple hazard indices are being adapted to level the level of radiation and the radiological impact corresponding to the values recommended by the IAEA (2010), ICRP (1999) and UNSCEAR (2008) and other relative agencies.Below listed the hazard incident that is conducted in this research and the results are listed in Table 2.

Radium equivalent activity
Radium equivalent activity (Raeq) was used for compare the specific activities of materials containing 40 K 226 Ra and 232 Th, and using a single quantity that consider into account the radiation hazards that are associated with them.The following formula is used (Beretka and Mathew, 1985;UNSCEAR, 2008)   =   + 1.43  ℎ + 0.077 (2) Where CRa, CTh, CK are the radioactivity concentration in Bq/kg of 226 Ra, 232 Th, and 40 K respectively.These materials whose Raeq concentration are to be exceeds 370 Bq/kg should be avoided due to radiation hazards (Beretka and Mathew, 1985;UNSCEAR 2008).
The results of the samples selected from EBS display that the maximum value is 370.1 Bq/kg representing sample SL2 (1st Separator) and, the minimum value is 45.2 Bq/kg representing sample TW10 (Treatment water) (Table 2), with an average value of 75.5±94Bq/kg.All values, except that of sample SL2, are consider to be acceptable and have no hazard impact since these values are consider to be lower than the standard guideline (370 Bq/kg) recommended by UNSCEAR (2008).

Gamma absorbed dose rate
The Gamma absorbed rate was computed using the concentrations of 40 K, 226 Ra and 232 Th in the soil.The values of 137CS, 90 Sr, and 235 U were omitted due to their anticipated negligible contribution to overall dose from environmental background.
Outdoor air gamma dose rate (D) at a height of 1 meter above ground could be calculated by the equation derived from Beretka and Mathew (1985).

Annual effective dose equivalent
The AEDE is determined by calculating engaged applying a dose conversion factor of 0.7 Sv/Gy and dose rate, along with the occupancy factor for outdoor exposure.For the current study, an assumption with totaling 2503 hours per year was considered within the workers time with oil production industry.The average annual effective dose equivalent received by an individual is conducted utilizing a conversion factor of 0.7 SvGy_1, which transforms the absorbed rate in Gy into effective dose equivalent in Sv.The AEDE is computed using the below equation: Outdoor (nSvy-1) = Absorbed dose (nGy/y) * 2503h * 0.7Sv/Gy (3) The area within EBS have maximum value of 1.1 mSv/y in the sample SL27 (1st stage of processing) and minimum value of 0.1 mSv/y Bq/kg in samples WW9 (wastewater) TW10 (Treatment Water).(Table -2 and Fig. 7).The average value is 0.6 which is higher the world average value of (0.45mSv/y) (UNSCEAR 2008).  2 and Fig. 8).All values of Hex are lower than the unity except those of site 2 (Fig. 7), so, most of Hex values are acceptable and have no hazard (Beretka and Mathew, 1985;UNSCEAR 2008).

Internal Hazard Index
Radon ( 222 Rn) is a radioactive noble gas that arises as a decay product of 226 Ra.It possesses of approximately 3.8 days half-life.Notably, 222 Rn constitutes half of radiation doses and presently recognized as a significant contributor to lung cancer risk.The internal exposure to Radon presented by the internal hazard index (Hin), calculated by the following: Hin= (A Ra)/185+( A Th)/(259 )+ ( A K)/4810 (4) Where: Ath, ARa, and AK are the mean activity concentrations of 232 Th, 226 Ra, and 40 K, respectively, in Bq. kg -1.The min value is in samples WW9 and TW10 where their values are 0.19 Bq/kg and the max value is within Samples SL2 (1st Separator), SE5 (2nd Desalter), and SE3 (2ed Separator) (Table 2 and Fig. 8) where their values are higher than unity the standard guideline (unity) (IAEA 1989).This indicated to be a not safe to work with.

Conclusions
Radioactivity of NORM and radiation doses and indices are investigated in the EBS oilfield in this study.Although some sites as in stage of separation, desalter stage and waste pit have NORM concentrations ( 232 Th, 226 Ra and 40 K) are higher the average of worldwide, the site is not considered radioactively contaminated or has significant radioactive hazards.The higher concentrations of Th-232, Ra-226 and K-40 were 83, 153.1 and 1264.2Bq/kg respectively, in sludge collected from the 1st separation stage with total radiation dose rate about 0.13 µSv/h.However, most of the sites recorded a dose of radiation less than the limits recommended by (IAEA) and UNSCEAR and other relevant authorities.This is the result of the fact that the site is a recent production of oil, in addition to the strict instructions, the application of environmental safety conditions strictly, and the removal of pollution first-hand, and transporting it to the specified landfill sites.Estimation of hazard indices indicates that all sites expect the first stage of separation have values below the IAEA and UNSCEAR.This does not preclude that there should be periodic monitoring of the places where oil production residues leakage occurs, especially in the isolation sites, 1st stage, and the salt separation sites in the later stages.In general, the site of the study area does not show radioactive contamination or significant radioactive hazards, as it is a new facility, and safety instructions are still strictly applied, and due to the removal of waste immediately before its spread by the workers in the facility.

Fig. 2 .
Fig. 2. sketch map showing the stages of oil and gas production in East Baghdad Oil Field.

Fig. 3 .
Fig. 3. Distribution of Ra-226 in selected samples from different locations in East Baghdad oil field

Fig. 5 .
Fig. 5. Distribution of K-40 in selected samples from different locations in East Baghdad Oilfield

Fig. 6 .
Fig. 6.Distribution of total exposure dose rate in different locations in East Baghdad Oil field

D
(nGy/h) =0.462CRa+0.621CTh+0.041CK(2) Where D(nGy/h) is the dose rate in Nano gray per hour and CTh, CRa and CK are the radioactivates in Bq/kg of 232 Th, 226 Ra and 40 K respectively.The minimum value inside EBS is 22.27 (nGy/h) which is Treatment water and Wastewater locations, while the maximum value 174.5 (nGy/h) was near sample SL2 location (thst is first stage 1st separator) (Table-2 and fig.7A), with an average of (97± 54 nGy/h) that is higher than the world average value of 58 nGy/h (UNSCEAR, 2008) The value D at the EBS was calculated from the measured radioactivity for (K-40, Ra-226 and Th-232) only.The radioactivity of radium-226.Ra-226 are the main contributors in gamma absorption dose (FIG.7B).

Fig. 7 .
Fig. 7. Absorbed doses rates (A) due to exposure to gamma rays emitted from Ra-226, Th-232 and K-40 in sampling locations.(B) Contribution of Ra-226, Th-232, and K-40 in total absorption dose rates in sampling locations

Fig. 8 .
Fig. 8. Annual effective dose equivalent caused by NORM for samples in the study area

Fig. 9 .
Fig. 9. External hazard index and internal hazard index caused by NORM for samples in the study area

Table 1 .
Activity of Ra-226, Th-232 and K-40 (Bq/kg) in samples selected from different locations in East Baghdad oil field

Table 2 .
The values of hazard indices result from existing NORM in samples from the study area.