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

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

Gulf of Mexico Seismic Refraction Study, Alaminos Canyon OBS Experiment (Final Technical Report)

The University of Texas Institute for Geophysics has conducted a study to examine the deep sedimentary and basement structure in the Alaminos Canyon area of the northern Gulf of Mexico using large-capacity air guns and ocean-bottom seismographs. We carried out a field experiment (Phase I) in early 1985, and have completed both the standard data reduction and analysis (Phase II) and more detailed advanced analysis of the acquired data set (Phase ill). This final report describes the field experiment and covers all the results including interpreted structural cross-sections along Lines A and B and description of the characteristics and interpretation of several converted shear waves observed using three-component instruments.Industry consortiumInstitute for Geophysic