[Biogenic elements and sulfate reduction in a flooded oil carbonate stratum]

Biogenous sulphate reduction and accumulation of secondary H2S were caused by the action of pumping waters with a low content of mineral elements on carbonate collectors with a high concentration of relict H2S during long periods of time. The amount of sulphates, phosphates, and ammonium nitrogen in water from layers of various mineralization is sufficient for active sulphate reduction. Sulphates and phosphates are eliminated from rocks of layers with diluted waters. The maximum increase of SO42- in waters was 1545 mg/litre, that of HPO42- was 0.34 mg/litre. The amount of ammonium decreases with mineralization of the layer waters, remaining within the range of 129-7 mg/litre. The content of CO2 and HCO3- increases in diluted waters to 197 and 695 mg/litre, respectively, correlating with biogenous processes. The highest number of sulphate reducing bacteria (dozens of thousands of the cells per ml) was found in water with mineralization of 19 g/litre. Curves for the content of SO42-, HPO42-, NH4+, and CO2 have a common maximum in waters of the Polaznensky deposit with a salinity of 62 g/litre.