Distribution Patterns of Porosity and Permeability in the Hydrocarbon Bearing Sands of the Niger Delta Continental Shelf
George A. Chiamogu1 and Olugbenga A. Ehinola2
1Geology, University of Ibadan, Ibadan, Nigeria
2Dept of Geology, University of Ibadan, Ibadan, Nigeria
Based on the wealth of subsurface data generated by the oil and gas industry in Nigeria, the characteristics, variability and distribution patterns of porosity and permeability were analyzed for the Niger delta continental shelf. Investigation depth ranges from 5000 feet to 16,000 feet , spanning the currently known hydrocarbon bearing interval in the region.
The study shows that the reservoir rocks are characterized by a wide range of porosity and permeability values. Porosity ranges from 3.6% to 39.4%, a mean of 21.92%, standard deviation of 8.91. The horizontal permeability ranges from 0.08 to 9990 millidarcy, mean of 1005.81 , standard deviation of 1948 while vertical permeability range from 0.01 to 7940 milidarcy, a mean of 606.5 and standard deviation of 1341.5.
There is an overall decrease of porosity and permeability with increasing burial depth at a rate of 2% every 1000 feet at the shallower level , lowering to 1-1.5% at greater depths(>12,000 feet). For a composite sandstone sequence representing a wide range of depositional environment and subsequent diagenetic histories, porosity shows an exponential relationship with horizontal permeability, but log relationship within a genetic sand unit, and linear relationship with clay content of the reservoir. Horizontal permeability (Kh) shows more or less log relationship with clay content and power-law relationship with quartz content of the reservoir sand
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