Thermal conductivity estimates in the Niger Delta using lithologic data and geophysical well logs

Thermal ock properties and heat flow were determined from 260 wells in the Niger Delta. The thermal conductivity data provides inputs for the determination of heat flow and for thermal evaluation of the Niger Delta basin. A map has been constructed using lithologic data and geophysical well logs to give an overview of its distribution. The thermal conductivity for sand and shale, the predominant lithology in the Niger Delta, shows wide variations from one well to another. In the Benin Formation, thermal conductivity has an average value of 8 W/mK. The lowest values are found offshore westward, while highest values occur northward. The conductivity values, however, decrease towards the marine paralic section, with an average value of 5 W/mK, the region of highest interest. The thermal conductivity values have been used in calculating heat flow. A significant regional trend of relatively low (20-30 mW/m2) heat flow at the central part of the delta, increases both seaward and northward (40-55 mW/m2). The lowest values of heat flow as low as 20 mW/m2 are recorded in the central part of the delta while the highest values exceeding 50 mW/m2 are recorded in the northern part of the delta. Knowl edge of thermal properties has direct relevance for hydrocarbon exploration. It has been established that the bulk of hydrocarbon accumulation in the Niger Delta is of thermal origin, hence the importance of this findings

Thermal State of the Niger Delta Basin

The Thermal State of the Niger Delta Basin is presented. Subsurface temperatures obtained from continuous temperature logs in 260 wells allowed to stabilize for several months were used in determining the Geothermal Gradients in the Niger Delta. Regional gradients are lowest (0.82oC/100m) at the central part of the Delta and increases both seaward and northward up to 2.62oC/100m and 2.95oC/100m respectively in the continental sands of the Benin Formation. In the Marine paralic deposition, Geothermal Gradients range from 1.83oC/100m to 3.0oC/100m at the central portions. The highest values of 3.5oC/100m to 4.6oC/100m are seen northward while intermediate values of 2.0oC/100m to 2.5oC/100m are recorded seaward. The thermal gradients are clearly influenced by the lithology or rate of sedimentation in the area. Regions of low thermal gradient correspond with areas of high sand percentage, primarily because sands are better conductors than shale and therefore show as low thermal gradient. The thermal conductivity for sand and shale, the predominant lithology in the Niger Delta show a wide variation from well to well. In the Benin Formation, conductivity ranges from 5 2 W/mK to 10 4 W/mK with an average value of 8 W/mK. The lowest values are found offshore westward, while highest values are northward. The central portion has between 6 – 10W/mK. The conductivity values however decreases when one approaches the Marine paralic section with an average value of 6 W/mK. A significant regional trend of relatively low heat flow at the central part (20 – 30 mW/m2) increases both seaward and northward (40 - 55 mW/m2) is observed in the area. The lowest heat flow is obtained in the central part of the Delta. The highest heat flow is in the northern part, with values exceeding 50 mW/m2. The present study has shown that temperature can be predicted as a continuous profile unlike the Bottom Hole temperature, which gives values for two or three data points in a borehole. The knowledge of thermal properties has direct relevance for hydrocarbon exploration

Mathematics, Physics and Computer SciencesTemperature variations in the Niger Delta subsurface from continuous temperature logs.

Continuous temperature data from 126 wells allowed to attain a state of thermal equilibrium for several months and 134 wells (stabilisation within thirty days) were used to determine the variations in temperature in the Niger Delta. At about 8,000 ftss., high temperatures of 80 - 120 ºC exist in the Northern and Ughellis depobelts, low temperatures of 46 – 88 ºC are recorded in the Central and Coastal depobelts, moderate temperatures 80 – 100 ºC are seen in the Offshore depobelt. At 6,000 and 4,000 ftss. similar trends are also evident. Regional geothermal gradients range from 1.5 – 2.5 ºC/100 m in the Coastal depobelt and Offshore regions and increases northward to 4.5 ºC/100 m. Vertical geothermal gradients show a continuous but non linear function with depth and increases with diminishing sand percentage from less than 1.0 ºC/100 m in the continental sands through 2.5 ºC/100 m in the paralic section to 5.0 ºC/100 m in the continuous shaly section. Higher gradients are associated with shaly formations primarily because of low thermal conductivity. Global Journal of Pure and Applied Sciences Volume , No 1 January (2001) pp. 137-142 KEY WORDS: Temperature variations, subsurface, temperature logs, sand percentage, depobelts

Geothermal gradients in the Niger Delta basin from continuous temperature logs

Subsurface temperatures obtained from continuous temperature logs in 260 wells allowed to stabilize for several months were used in determining the geothermal gradients in the Niger Delta. Regional gradients are lowest (0.82oC/100m) at the central part of the Delta and increases both seaward and northward up to 2.62oC/100m and 2.95oC/100m respectively in the continental sands of the Benin formation. In the marine paralic deposition, geothermal gradients range from 1.83oC/100m to 3.0oC/100m at the central portions. The highest values of 3.5oC/100m to 4.6oC/100m are seen northwards while intermediate values of 2.0oC/100m to 2.5oC/100m are recorded seaward. The thermal gradients are clearly influenced by the lithology or rate of sedimentation in the area. Regions of low thermal gradients correspond with areas of high sand percentage, primarily because sands are better conductors than shale and therefore show as low thermal gradients. There is a continuous but non-linear relationship between geothermal gradients and depth, from less than 1.0oC/100m in the continental sands through 2.5oC/100m in the marine paralic section to 5.0oC/100m in the continuous shaly section. Key words: Geothermal gradient, temperature, sand percentage, heat flow (Global Journal of Pure and Applied Sciences: 2003 9(2): 265-272