Prediction Of Overpressure From Porosity Estimation In Sedimentary Rock Formation In Western Niger Delta, Nigeria

Overpressure prediction is vital for safety during exploration and drilling activities. Porosity indicates the potentiality or fluid storage capacity of rocks. It is the first among essential attributes of a reservoir. This study is aimed at predicting overpressure from porosity estimation in sedimentary formation and was carried out using well log data comprising of gamma ray, density and sonic logs from two exploratory wells in Niger Delta. Gamma ray log was used to delineate the lithology of the sedimentary sequence into sandstone and shale beds at the pre-determined depth intervals, porosity was estimated from interval transit time obtained using sonic log while overpressure was estimated using empirical relation. The results of this study show that porosity decreases with for both sandstone and shale beds, but however, porosity inversion was observed between the depth range of 2100ft and 3171ft. Overpressure zone was detected at the depth range of 2195ft and 3200ft at porosity value from 28% to 32% and 22% to 31% for sandstone and shale bed respectively. The knowledge of this study can be applied in the prevention of drilling activity hazards (blow out and lost circulation) and sedimentary basin analysis.