Abstract
Geothermal gradient and heat flow were computed from bottom hole temperatures in an oil field in Niger Delta, Nigeria. The statistical analysis of computed geothermal data was carried out. The computed geothermal gradient vary from 17.3±0.14 to 24.33±0.70°C/Km with an average of 22.24±0.57°C/km. The heat flow ranges from 38.06±0.31 to 56.39±2.41 mWm-2 with an average of 50.15±1.25 mWm-2. The computed variance of the geothermal gradient and heat flow are 0.499 and 2.447 respectively. The standard deviation for the geothermal gradient and heat flow are also 0.79 and 1.564. The values of the geothermal gradient and heat flow are low in the south and high in the northern parts of the field. The geothermal values increase towards the north. The possible causes of geothermal anomalies are variation in thermal conductivity, presents of geological structures such as growth faults and rollover anticlines and movement of fluid in the subsurface. The least geothermal gradient and heat flow values occur in the edge of the south east region. The region with high heat flow may be attributed to low sedimentary thickness while area with low heat flow may be associated with high sedimentary thickness. The geothermal analysis shows that the sediments in the area has attained hydrocarbon generation stage of temperature interval of 150 to 300°F (65 to 150°C). In the concept of the hydrocarbon-liquid window, the depth range within which liquid hydrocarbons are likely to be present is 1550-4500 m.
Highlights
The study of subsurface temperature, geothermal gradients and heat flow is crucial in understanding the thermal maturation of sediments and the past thermal regimes in a basin
The heat flow increases from the south towards the north with the least heat flow occurring in the edge of the south east
The basic statistical techniques applied to the data are mean, variance, standard deviation and error analysis
Summary
The study of subsurface temperature, geothermal gradients and heat flow is crucial in understanding the thermal maturation of sediments and the past thermal regimes in a basin. The temperature history of a sedimentary basin controls it’s maturation and its subsequence conversion to hydrocarbon. The sources of heat in a sedimentary basin are the heat flow from the earth’s interior and those generated by the radioactive elements present in the sediments. The thermal history of a sedimentary basin is related to the processes of basin formation (Sleep, 1971). Heat flow is usually transfer from the basement rock into the overlying sedimentary sequence. The temperature in sedimentary basin increases downwards with depth while heat is transported upwards by a process known as heat flow. Heat flow is mainly transported in sedimentary basin by conduction
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