CLAY MINERALOGY OF THE FORMATIONS OF THREE OFFSHORE WELLS IN THE WESTERN AND CENTRAL BLACK SEA REGION, TURKEY

Clay mineral analyses in the petroleum industry have great importance especially for explorations of oil possibilities in a target area. Some kinds of clay minerals are used as indicators to determine the temperature of oil bearing formations, or to determine the diagenetic conditions of the formations in the area. This temperature and diagenetic condition information is significantly important for understanding the maturity of the oil that is expected to be extracted from a selected area.

Some clay minerals like illite, which contains potassium ions in its structure, can be used as an indicator to understand the burial temperature and pressure of a formation. Smectite, which is a clay mineral formed under surface conditions, starts to convert to illite under increasing temperature and pressure resulting from deep burial. This conversion is basically from the replacement of sodium ions by potassium ions under heating, because a sodium ion is not durable in the structure of a smectite but a potassium ion can be placed in its structure and the new product after the ionic conversion becomes illite.

The Black Sea region has the possibility to contain some petroleum sources under its abyssal plain. The Turkish Petroleum Corporation has many offshore wells along the Turkish shoreline of the Black Sea and we are working on the clay mineralogy and geochemistry of the two wells from the central and one well from the western side of the Black Sea region in Turkey. In this study, we will find out the clay mineralogy and geochemical characteristics of the three wells and we will present a relationship between the diagenetic conditions of the formations of those three wells. By understanding the relationship between the formations, we will interpret the occurrence of the environment that contains the clay-bearing formations. Initial research has been done with X-Ray Diffraction (XRD) in order to determine the clay mineralogy of samples and with X-Ray Fluorescence (XRF) in order to determine the concentrations of major and trace elements of samples. Data from XRD show a slight decrease in the amount of smectite minerals and a slight increase in the amount of illite minerals with increasing depth, and XRF data similarly show a slight decrease in sodium values and a slight increase in potassium values with increasing depth in the three wells.