Predicting Zones of Overpressure in Coastal Swamp Depobelt of Niger Delta Nigeria, Using Well-Log and Seismic Data

Abstract

Sixty overpressure zones were established in eighteen wells in the EKON and IDUMA fields. The predicted zones gave insight into the determination of overpressure origin and mechanism within the Coastal swamp Depobelt. Results show that increased bulk density observed from the sand sequences at greater depths indicated compaction. Faults and horizons mapped revealed the segregation of wells with similar hydrocarbon contacts into various pressure compartments. This indicated overpressure zones. Also, the good ratings of petrophysical properties within the reservoir units were pointers to overpressure regions. Over pressured zones predicted from the Eaton sonic transit time model tallied with the outcome of results obtained using the seismic method. In addition, the reservoir tops conformed to the upper limits of overpressure while their bases coincided with the lower limits of overpressure. Results obtained from this study, confirmed compaction disequilibrium as the primary mechanism of over-pressure while tectonism and hydrocarbon gradient were inferred as secondary mechanisms.