Date of Award
Master of Science (MS)
Dr. Esam Abdel-Gawad
Dr. Abdulrazag Zekri
Dr. Tarek Youssef
During a period of 28 years, more than 96 million m3 of oilfield produced water was re-injected in the shallow aquifer at Marmul oilfield area, and changed groundwater characteristics. The 10 wells of Shallow Water Disposal (SWD) have been used to inject water in shallow groundwater aquifers of Dammam and Rus formations. The disposal of oilfield produced water to shallow aquifer has been continuing since 1980, with approximately 96 Mm3 of produced water having been disposed and an estimation of approximately 9600 m3 oil has been disposed of in this case until the beginning of 2008.
The present thesis aim is to quantify and assess the organic and inorganic pollutants in the study area. In this study, the hydro geochemical data from 19 Monitoring Wells (MWs) and from Marmul Main Production Station (MMPS) were used to assess the lateral effect in the shallow groundwater.
The Total Petroleum Hydrocarbon (TPH) concentrations ranged from 0.170 ppm and 1.582 ppm with average of 0.435 ppm. The concentrations and distribution of total Poly Aromatic Hydrocarbons (PAHs) in the Marmul study area were measured in MWs ranged between zero ppm and 0.806 ppm. There are 7 individual PAHs observed in the monitoring wells of the studying area. Naphthalene has the highest concentration among other individual PAHs with 0.616 ppm and the lowest concentration is Fluorine with concentration of 0.004 ppm. The distribution of TPH and PAHs in the area trend is to increase toward the area of disposal of brines in the shallow aquifer. Also, water sample collected from well no. MW-10 which is located north of the SWD has shown high concentrations in both TPH and PAHs over the study area.
The Gas Chromatography (GC) device fingerprints of the sampling indicated that the type of petroleum hydrocarbons is same and it is similar to the one from MMPS. In this case, the source of organic pollution in the area is attributed to the activity of oilfield brines disposal of in shallow aquifer. All fingerprints contain around 19 of hydrocarbon compounds from C21 to C39 and did not include prestane or phytene isprenoids. The Carbon Preference Index (CPI) in samples of the study area was ranging from 0.6 to 1.7 with average of 1.18, reflecting in almost similar anthropogenic sources of pollution rather than biogenic.
All water samples is close together marginally except well no. MW-15. So, the result of major ions in MWs without well no. MW-15 range between 0.1 to 36 meq/l for Ca, 1 to 27.75 meq/l for Mg, 7.5 to 65.5 meq/l for Na, 8.89 to 67.7 meq/l for Cl, 1 to 52.9 meq/l for SO2, and 0.5 to 10.58 meq/l for HCO3. The dominant water type is Ca and Mg-chloride and sulfate and a few water samples belong to the Na and K-carbonate and bicarbonate types. Because the Cl and Ca are dominant, the groundwater may result from reverse ion exchange of Na+ - Cl- waters and in generally the water type is Ca-Mg-Cl-SO4.
The distributions of major ions in the study area are roughly similar to each other and brightly showing the effect of re-injected in the groundwater and they predict that the point source of the groundwater is the same source.
The majority of the collected samples have Ca/Mg ratio of more than 1.0 (average 1.95), indicating exposures of carbonate rocks in the area. Similarly Na/Cl ratio are below 1.0 (mean 0.95) indicating fresh water existence. In consideration, the results of MMPS produced water samples have average Na/Cl ratio of 1.1 and average Ca/Mg of 0.1, suggesting no influence of this water in the groundwater in side of Na and Cl.
There are 11 trace metals in results of concentration. The highest concentration detected was for the dissolved SiO2 with an average amount of 24.79 ppm, which may attribute to chemical weathering of siliceous minerals in the groundwater. The lowest concentration average is for Co of 0.0002 ppm and it’s detected in only one monitoring well. The average concentrations of the rest of 9 trace metals are ranged between 0 to 1.2 ppm (Sr 11.56 ppm, B 1.18ppm, Mn 0.08 ppm, Ba 0.03 ppm, Mo, Zn, and P at 0.02 ppm, V 0.004 ppm and Cr 0.002 ppm). No concentration of Cd, Pb, Al, Fe, Cu and Ni were found in the study area. In addition, trace metals’ results may regard to anthropogenic and/or natural sources and its level not indicated as trace metal pollution case.
Groundwater salinity zones display an increase in salinity towards the north west of the study area. This increase may correspond to the groundwater flow direction and probably reflects increasing residence time and dissolution of salt into the groundwater or polluted by poorer quality. The reason it may reflect the type of bedrock in the formation as dolomite, limestone, gypsum or another type that cause increasing of groundwater salinity. There is difference in salt concentration in north to north east of the SWD area and this adjustment with the groundwater movement from Dhofar Mountains to the Nejd plateau.
There is fluctuation in the water table in the study area and it correlates well with variations in high disposal volumes over the disposal period. While water level in the SWD area is in high level which tends to the response of disposal volumes of produced water.
Patterns in groundwater pollution are consistent with produced water contamination that affirms the pollution is originating from one source (point source) of a produced water re-injection disposal wells in the study area. The pollution plume appears to be migrating northeast along the direction of groundwater flow. When PDO handled the option which serve with the least environment impact and phase out of the SWD in 2008, it should be do the several measurements to mitigate of the GWP in Marmul SWD area.
Sakroon, Salim Ahmed, "Effect of oilfield brine on groundwater quality in Marmul area, Sultanate of Oman" (2008). Theses. 379.