An Estimate of Oil Window in Nigeria Niger Delta Basin from Recent Studies
J.O. Adedapo, A. E. Ikpokonte, K. Schoeneich, E. Kurowska

Abstract
Niger Delta sedimentary Basin is a large arcuate delta of the destructive dominated wave type that has been explored for oil and gas and exploited since 1958. During the following decades the temperature measurements in boreholes were an important element of the hydrocarbon prospecting. In this paper, subsurface temperatures measured from continuous temperature logs in six hundred and wells drilled to date were used for the study of natural subsurface temperature of rock formations after applying the appropriate temperature correction factors. Geothermal gradients are then calculated and best presented on maps, to show the flow direction of the subsurface heat. Then, the depths to temperature range of the oil and gas generation (windows) in the Delta were assessed and presented on the maps for temperatures of 65^OC, 100^OC and 150^OC. Minimum geothermal gradient value of 1.2^OC/100m is found at the central part of the basin while maximum value is 7.62^OC/100m obtained at the northeastern part of the basin, very close to Abakaliki anticlinorium, Oban massif and Afikpo syncline showing regions of high heat. The mean background geothermal gradient value over the area is 3.29^OC/100m; median is 2.53^OC/100m. The interpretation of the minimum depths (2-4km) to temperatures (65^OC to 120^OC) contour maps constructed shows that about 80% of the total area of Niger Delta favour the generation of hydrocarbons generation. These results also show that higher temperatures (120-150^OC) necessary for hydrocarbon gas generation are obtainable therein at shallower level in the north to northeastern and eastern parts of the basin. This study confirm the fact that temperature depth data can be used to further prospect for hydrocarbon in other parts of the sedimentary basin.

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