Geothermal Gradients and Heat Flow Variations in Parts of the Eastern Niger Delta, Nigeria

Abstract

Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom – hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1–D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29 – 55 mW/m2 (0.69 – 1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures.

Source rock maturity and petroleum generation in the Dahomey Basin SW Nigeria: Insights from geologic and geochemical modelling

“…Borehole temperature data of the two studied wells were not available. Nevertheless, the average geothermal gradient 39.6 °C/km -1 of the neighbouring Afowo-1 well located on coast north of the X well (Avbovbo, 1978, Onuoha andOfoegbu, 1987), the heat flow of 59.5 + 10.9 mW/m 2 in the Gulf of Guinea area (Herman et al, 1997), the heat flow of 50mW/m 2 reported along the margin of Cote d'Ivoire, Togo and Nigeria, (Macgregor et al, 2003) and the average heat flow of 42.5 mW/m 2 in the contiguous Niger Delta (Odumodu and Mode, 2016) were used as control for the initial modelling based on their proximities and similar tectonic history with the Dahomey Basin. The geothermal gradient in the Afowo-1 (Dahomey Basin) and average heat of Gulf of Guinea basins was described to be higher than some part of the contiguous Niger Delta Basin.…”

Evaluation of poisson’s ratio range for Fracture Pressure Gradient (FPG) prediction for Niger Delta formation

“…The lithostratigraphy of the Tertiary Niger Delta can be divided into three major units; Akata, Agbada, and Benin formations with depositional environments ranging from marine, transitional and continental settings respectively. Their ages range from Eocene to Recent, but they transgress time boundaries [8]. This region due to its hydrocarbon proliferation, then has 'depo-belts'; depositional belts or "depo belts" consists of a series of off-lapping siliciclastic sedimentation cycles or mega-sedimentary belts.…”

“…Evammy, et al [9] referred to this structure as mega structure while [10] were the first to call them depo-belts. There are seven regional depo-belts which are discerned along the north-south axis of the Niger Delta, each with its own sedimentation, deformation and petroleum history [8], and the activity in each depo-belts has progressed in time and space toward the south-south west through stepwise alluvial progradation facilitated by large scale withdrawal and forward movement of the underlying shale. These depo-belts include; the Northern Delta, the Greater Ughelli, the Central Swamp I&II, the Coastal Swamp I&II, and the Offshore depo-belts [8].…”

Curie point depth and heat flow deduced from spectral analysis of magnetic data over Adamawa volcanic region (Northern Cameroon): geothermal implications

“…Several researchers used magnetic data to evaluate spectral CPD in different parts of the world in order to explore gas, oil and others resources [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. In this paper, we estimate CPD, geothermal gradient, and heat flow values using spectrum analysis of the Grid Earth Magnetic Anomaly (EMAG2) for geothermal investigation in the Adamawa volcanic area.…”