PORE-PRESSURE PREDICTION FROM SEISMICS: A Case Study of an X-Field in the Niger Delta
*Nfor Bruno Ndicho Department Of Geology, Ojukwu University, Anambra State, Nigeria
*Corresponding Author: Nfor Bruno Ndicho
Department Of Geology, Ojukwu University, Anambra State, Nigeria Email:email@example.com
Published on: 2018-06-27
In this work Pore pressure prediction of an X- oil field in Niger Delta Basin was evaluated from seismic reflection data, using the Bower’s and Gardner’s technique of velocity- to-pore pressure gradient. Results show that, the top of overpressure zone is lies at depths varying from 1500m in well 01, through 2048m in well 03 to 1722m in well 05. Sonic log deflections at these intervals all showed significant deflection common with pore pressure zones. These overpressure zones are interpreted to correspond to the Comparison of the overpressure zone with available geophysical logs shows that the interval is under-compacted and has lower bulk density, low interval velocity and high porosity. Considering the young age of the basin, these overpressure zones are attributed to low mechanical compaction, chemical compaction and hydrocarbon generation zones, associated with shale-rich region of the Agbada Formation of the Niger Delta basin. The advantage of pore- pressure prediction from seismic is that, it provides alternative method of determining the expected pressure in a location where there are no well data, or even in areas where there are logs; it complements the prediction that is based solely in offset well logs. The seismic velocity intervals were derived from the seismic check-shot data. The computed pore pressure results derived from seismic were later compared with the available sonic and resistivity logs of the boreholes. Parameters in the velocity-to-pore pressure transform were then estimated using the seismic interval velocity.
The importance of reservoir pressure in hydrocarbon exploration and exploitation has drawn attention of petroleum geoscientists and reservoir engineer scholars due to the obvious need to make the petroleum Industry environmentally friendly. Opara and Onuoha (2009), opinioned that health hazards due to kicks and mud loss during drilling pose industrial challenges. Opara and Onuoha (2009) suggested that accurate overpressure zone prediction is vital for successful and safe drilling of wells. Before now, the practice has been to monitor overpressure zones during drilling, with attendant consequences of unpreparedness to combat extremely high pressure zones. The potential high impact of drilling through overpressure zone and its implication on cost, health and ecological system thus necessitates an alternative method of pre-drilling pressure zone detection from seismic data. The advantage of pore- pressure prediction from seismic is that, it provides alternative method of determining the expected pressure in a location where there are no well data. Even in areas where there are logs, it complement the prediction that is based solely in offset well logs. This study thus attempts to predict pore pressure belt of X Oil field from seismic data. This information on pore pressure condition of a field, even before drilling, enhances better safety preparedness by the drilling crew prior to actual drilling.