Heavy crude oil from the Mukhaizna oil field in Oman was emulsified with water in an attempt to decrease its viscosity. The oil has a kinematic viscosity of 7160 mm 2 /s at 30 °C, density of 0.9571 g/cm 3 at 15 °C, and asphaltene content of 4.7 wt %. The effects of changes in water content (20-30 wt %), type and concentration of surfactant, addition of a water-soluble polymer, and agitation temperatures (25 and 42 °C) were studied in order to identify the optimum viscosity and stability for transporting the oil. The stability was measured by the water separation rate from the emulsion. For the Mukhaizna heavy crude oil, 21-22 wt % of water content and 0.4 wt % of nonylphenol ether type or higher alcohol alkylene oxide type surfactant were found to be optimum for a stable emulsion with a concomitant significant decrease in viscosity to about 1 / 3 -1 / 4 that of the original crude oil. This improves the transportability of the heavy crude oil and makes it suitable for use as a power generation fuel.

Summary As an oil field matures, it produces larger quantities of produced water. Appropriate treatment levels and technologies depend on a number of factors, such as disposal methods or usage aims, environmental impacts, and economics. In this study, a pilot plant with a capacity of 50 m3/day was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. The flexible design of the plant allows for the testing of different combinations of these processes on the basis of the requirements of the water to be treated. The subject water during this study was a complex and changing mixture of brine and oil from different oil fields. Induced-gas-flotation (IGF) trials were conducted, with different coagulant [poly-aluminum chloride (PAC)] -addition rates from 0 to 820 mg•L-1. Inlet-dispersed oil-in-water (OIW) concentrations were quite varied during the trials, ranging from 39 to 279 mg•L-1 (fluorescence-analysis method). Turbidity also varied, ranging from 85 to 279 FTU. Through coagulation/flocculation and flotation, dispersed oils were removed from the water. PAC addition ranging from 60 to 185 mg•L-1 resulted in the reduction of the dispersed-oil concentration to less than 50 mg•L-1 in treated water; and PAC addition ranging from 101 to 200 mg•L-1 resulted in the reduction of the dispersed-oil concentration to less than 15 mg•L-1 in treated water. Turbidity was also reduced through flotation, with trial average reductions ranging from 57 to 78%. Filtration further reduced turbidity at rates greater than 80% through the removal of any suspended solids remaining from flotation. Activated-carbon adsorption reduced OIW concentrations of flotation-/filtration-treated water to 5 mg•L-1 (infrared-analysis method) through the removal of dissolved oil remaining in the water. Results confirmed that such adsorption treatment would be more practical for water with lower chemical-oxygen-demand (COD) concentration because high-COD concentrations in water reduce the lifetime of activated carbon dramatically.

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Water table dynamics, dissolved oxygen (DO) content, electrical resistivity (ER) in monitoring wells and air pressure in the vadose zone are monitored in air sparging (AS) accompanied by soil vapor extraction (SVE) at a hydrocarbon-contaminated groundwater site in Oman, where a diesel spillover affected a heterogeneous unconfined aquifer. The formation of a groundwater mound at the early stage of air injection and potential lateral migration of contaminants from the mound apex called for an additional hydrodynamic barrier constructed as a pair of pump-andtreat (P&T) wells whose recirculation zone encompassed the AS and SVE wells. In all monitored piezometers the phreatic surface showed a rapid and distinct peak, which is attributed to the time of air breakthrough from the injection point to the vadose zone and a relatively mild recession limb interpreted as a decay of the mound. Tracer tests showed a layer of a relatively low hydraulic conductivity at an intermediate depth of the screened interval of the wells. Increased levels of DO and borehole air pressure that have been observed (as far as 50 m away) are likely mitigated by SVE and P&T. Radius of influence can be indirectly inferred from ER and DO changes in the AS operation zone. Salt tracer tests have shown that groundwater velocity within the AS zone decreases with the increase of air injection rate.

Joint research between Sultan Qaboos University, Oman, and Petroleum Energy Center, Japan; sought to develop and establish a process whereby the large quantities of produced water from Omani oil fields can be effectively treated and utilized for irrigation. During pilot plant operation, oil contamination ranging from 50–300 ppm, was reduced to below 0.5 ppm. Irrigation with treated water showed no significant detrimental effects on the growth of three different salt tolerant species of plants. Introduction Produced water is the largest single associated waste product of oil production. It is a common phenomenon to find a water layer below an oil layer. Thus, oil production is usually accompanied by water. Total production of water is expected to be more than ten times that of oil, during the economic lifetime of an oil field1. A salient feature of oil production in Oman is the fact that the output of water already exceeds that of oil in most of the wells. During 1999, Petroleum Development Oman (PDO), which holds roughly 95% share of total oil production in Oman, produced an estimated 450,000 m3/day of water as an associated co-product of its oil output of 135,000 m3/day. This volume of water is expected to increase steadily and double to 900,000 m3/day within ten years2. While in the northern oil fields of Oman, the separated water is re-injected into the oil bearing strata to maintain the reservoir pressure; in the southern oil fields, produced water has been disposed into the shallow water bearing strata in the past. However, due to fears of contamination of groundwater for human use with continued long-term shallow disposal, the government has prohibited this practice and all water disposal is being switched to deeper water bearing strata. Table 1, shows the PDO disposal history and forecast in the main oil fields in southern Oman. Beyond the year 2000, produced water disposal from these fields is expected to exceed 300,000 m3/day2. This volume is sufficient to irrigate 3000 hectares in an arid climate such as Oman. Although produced water is separated from oil in gravitational separation tanks and CPI separators, such water still contains 100–300 ppm oil. Table 2, shows the average oil concentration in produced water of south Oman oilfields2. While continued disposal of such produced water to shallow aquifers will result in groundwater contamination, disposal to deep aquifers is costly.

Polymer enhanced oil recovery (EOR) operation has been implemented for the production of oil from difficult mature oilfields in Oman. The polymer used in this EOR technique to sweep oil toward production wells is resulting in the generation of polymer flood produced water (PFPW) of increasing viscosity. Current methods of treating oilfield produced water must be reconsidered for the effective treatment of such PFPW of changing quality. In a previous study, the utilization of polyaluminum chloride (PAC) chemical was proposed for the coagulation of oil in produced water to be separated by flotation and filtration. As such, laboratory tests were conducted to evaluate the applicability of PAC and other chemicals for treatment of PFPW that has higher viscosity than ordinary oilfield produced water. These tests clearly indicated that aluminum sulfate (AS) chemical was more effective for treatment of such higher viscosity water. A pilot plant developed during the earlier study, was utilized to conduct coagulation/flocculation, flotation, filtration, and adsorption treatment trials for PFPW from an oilfield where polymer EOR is underway. For the final trial, the inlet PFPW viscosity was 1.4 cP at 40 °C and oil concentration was above 200 mg·L−1. AS was applied for coagulation/flocculation and flotation stages, and was found to be effective in reducing oil concentration to 1 mg·L−1. Filtration and adsorption stages resulted in further improvement of water quality. Most of the polymer used for EOR was believed to have been removed along with oil and suspended solids.

Polymer-enhanced-oil-recovery (EOR) operation has been implemented for the production of oil from difficult mature oil fields in Oman. The polymer used to sweep oil toward production wells in this EOR technique is resulting in the generation of polymer-flood produced water (PFPW) of increasing viscosity. Current methods of treating oilfield produced water must be reconsidered for the effective treatment of PFPW of such changing quality. In a previous study, the use of polyaluminum chloride (PAC) was proposed for the coagulation of oil in produced water to be separated by flotation and filtration. As such, laboratory tests were conducted to evaluate the applicability of PAC and other chemicals for treatment of PFPW with higher viscosity than ordinary oilfield-produced water. These tests indicated clearly that aluminum sulfate (AS) was more effective for treatment of such higherviscosity water. A pilot plant developed during the earlier study was used to conduct coagulation/flocculation-, flotation-, filtration-, and adsorption-treatment trials for PFPW from an oil field at which polymer EOR was under way. For the final trial, the inlet PFPW viscosity was 1.4 cp at 40°C and oil concentration was greater than 200 mg/L. AS was applied for the coagulation/flocculation and flotation stages, and was found to be effective in reducing oil concentration to 1 mg/L. Filtration and adsorption stages resulted in further improvement of water quality. Most of the polymer used for EOR was believed to have been removed along with oil and suspended solids.

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