The Environmental Impact of Oilfield Formation Water on a Freshwater Stream in Nigeria

A comparative analysis of the physico-chemical parameters of treated oilfield formation water and that of a freshwater stream with no previous history of pollution from oil exploration activities was determined. The environmental impact resulting from the discharge of treated oilfield formation water into freshwater samples collected from this stream with no previous history of pollution from oil exploration activities was assessed in terms of changes in water quality parameters such as Dissolved oxygen (DO), Biochemical oxygen Demand (BOD) and in the microbial populations of the freshwater samples over a period of seven days since oilfield formation water readily mixes with flowing water after discharge. The analyses showed that concentrations of constituents such as chloride, total dissolved solids, total hardness, nitrate nitrogen and ammonium nitrogen alkalinity and silicate of the oilfield formation water were much higher than those of the freshwater source. The oxygen uptake (BOD values) in some stations of the freshwater stream differed significantly only at the 5% level after the treatment. Generally, the microbial populations were also lower after the treatment. Such observations suggest that, there is reduction in the biological activities of the freshwater after the addition of the treated oilfield formation water. @ JASEM Formation water (also called produced water, oilfield brine, oilfield waste waster or connate water) is water that occurs in association with oil and gas in reservoir rocks and is present in the rocks immediately before drilling. The consensus among geologists is that Formation water originated from prehistoric seas (Chilingarian and Yen, 1978). Offshore drilling for oil and gas produces large amounts of Formation water, which is usually discharged into the aquatic environment. Water co-produced with oil and gas and separated for discharged retains up to 50 mg/L of separate-phase oil as small droplets and also may contain up to 35 mg L of dissolved hydrocarbons (Koons et al., 1977). The relative amount of hydrocarbons contributed to the aquatic environment by oilfield-produced waters is so small that any overall environmental effects from these inputs should be minimal (Koons et al., 1977). However, the numerous inorganic and organic constituents dissolved in the Formation water can be potentially or actually far more hazardous than the crude oil itself (Wardley-Smith, 1979). The ecological health of many river systems is threatened by the discharge of toxic compounds and the accumulation of these contaminants in these aquatic environments (Pruell et al., 1990). In Nigeria, sources of contamination are known to include industrial effluents sewage outfalls, urban runoff, rivers and atmospheric deposition. Many freshwater river systems have been classified as unfit for human consumption by the Federal Environmental Protection Agency (Onu, 1991). The recent introduction of environmental pollution discharge charges by the Lagos State Government is an effort to arrest the continued degradation of the environment through the discharge of untreated industrial wastes (Uwejamomere, 1991). The largest contributors are the petroleum and petrochemicalbases industries. In Nigeria were oil exploration activities are being carried out, Formation water is one of the major pollutants of the aquatic environment, which has now attracted much attention of the public. Unlike oil which forms a slick, Formation water readily mixes with flowing water after discharge, Collins (1975; 1980), Koons et al., (1977) and Hunt (1979) provide extensive data on Formation water from many oilfield locations. Nigeria oilfield Formation waters contain 3,000 to 9,000 mg/L chloride ions (Ibiebele, 1985; Oteri, 1985) and the continuous discharge of such wastewaters into a freshwater environment could cause major damage to aquatic and agricultural resources. Courant et al. (1985) provide extensive data for water-type classification for the Niger delta river and creek waters. These are areas that have experienced oil exploration activities over the years. The few oil pollution studies that have been carried out were mainly based in the Niger Delta areas (Snowden and Ekweozor, 1987; Obire, 1988; 1990). These areas have experienced oil exploration activities over the past 30 years. Reliable baseline data for use in assessing the impact of oil production activities are thus completely absent. Pollution incidents are generally monitored in a questionable manner involving measurements taken only after the occurrence of the incident (Snowden and Ekweozor, 1987). In recent years, oilfield formation water has *Corresponding author