干旱区生态环境知识资源中心

The two soil profiles of Al-Ahmadi and Burgan oil fields are alkaline arid soils with similar pH values and bicarbonate contents. Differences between the carbonate (CaCO3), exchangeable cation and sulphate contents of the two soil profiles are attributed to the diversified sources of the soils. Carbonate increments in topsoils of both profiles were probably derived from the new sand dunes formed after the Gulf War and migrated to the vicinity of the study area. Elevated concentrations of calcium, magnesium and potassium cations in topsoils were most probably supplied from the cation-rich formation water associated with the oil spilled in the two fields. The values of pH, electrical conductivity and sodium adsorption ratio for the two soil profiles classify them as saline soils. The high and similar proportions of sodium and chloride ions adsorped in the topsoils and the high salinity of both profiles indicate the accumulation of salts due to the flooding of soils by formation water and sea water used in controlling well fires. The downward oil/water movement and salt accumulation are restricted to the upper (25-95 cm) layer in the Burgan soil profile, whereas oil/water ganglia and associated salts spread over greater depths (150-270 cm) in Al-Ahmadi profile due to variations in the sorting, structure and hydraulic conductivity of the two soils. The sharp decrease in salt concentration below the Gatch (caliche) layer suggests that this layer acts as a moisture barrier impeding any further downward movement for oil/water and associated salts. Gypsum is the prime source of sulphate concentrations in the lower layers of the two soils. The flooding of oil fields by oil lakes containing sour crude and the dry deposition of SO2 gas emitted as soot from the burnt oil could provide source to the sulphate concentrations in the topsoils of both profiles.