Abstract

Drilling muds and cuttings derived from Ewan and Dibi off-shore wells in the Niger-Delta petroleum province of Nigeria was studied in order to evaluate their toxicity and possible environmental impacts that may result from their indiscriminate disposal. Oil based drilling wastes (muds and cuttings) were collected at prescribed depths and analyzed for aliphatic hydrocarbon (AH) and polynuclear aromatic hydrocarbon (PAH) using Gas Chromatography Mass Spectrophotometry (GCMS) method. However, both oil based and water-based drilling wastes collected from the same depth were analyzed for metals (iron, copper, zinc, lead, nickel, chromium, manganese, calcium, potassium and magnesium) using Atomic Absorption Spectrophotometry (AAS) method. Results showed that the values of total petroleum hydrocarbon in the two off-shore wells were in the range of 1,004.95 – 2,052.69 mg/kg for the cuttings and 5,759.11 – 6,546.01 mg/kg for the drill mud. It was observed that the concentration ratio of the polynuclear aromatic hydrocarbon to the aliphatic hydrocarbon in the total petroleum hydrocarbon (TPH) is in the ratio of 1:1000 for both the cuttings and drilling muds in both wells. Most of the total petroleum hydrocarbon (TPH), polynuclear aromatic hydrocarbon (PAH) has been found to be relatively lower than the World Health Organization standards. The drill wastes of the Dibi and Ewan off-shore wells also contain high concentration of iron (349.50 mg/kg) calcium (193.72 mg/kg), magnesium (87.50 mg/kg) and potassium (49.31 mg/kg) in that order. It is likely that the drill muds and cuttings wastes will increase the pollution problems in aquatic environment, thereby causing stress for the fish and other aquatic organisms. Therefore, disposal of cuttings and drilling wastes into the offshore environment should be totally discouraged and avoided.

Key words: Drilling muds, cuttings, toxicity, petroleum hydrocarbon