Reservoir Characterization from Abnormal Pressure in Parts of Eleme, Southeastern Nigeria, Using Well Log Data

Pressure in Geophysics is mostly explained in terms of hydrostatics. It is a three dimensional stress state in which the magnitude of stress is the same in all directions. The pressure of a fluid is said to be “abnormal pressure” if it is greater or lower than normal. Normal pressure is regarded as the rate of increase of formation density where the pore pressure remains hydrostatic. The determination of zones of abnormal pressure was done using geophysical well log method in the Eleme area. Sonic log and density log formed the porosity log and consequently the porosity data. The logs were interpreted and plotted against depth. The trends were analysed for wells and abnormal pressure. Overpressure was determined in between particular depths. For the two wells used, it is found between 2185m and 2785m for well A and 1805m to 2525m for well B. Abnornally high pressure zones have density of formation greater than 1.07kg/cm3. They also have pressure gradients exceeding hydrostatic pressure gradients of 0.433psi/ft to 0.435psi/ft for fresh and brackish water with less than 20000ppm of salt and 0.465psi/ft for salt water with about 80000ppm salt content. The determined abnormal pressure can be taken as a guide in the Eleme area of Nigeria when oil wells are to be drilled.