Determination of Geothermal Gradient from Bore Hole Temperature data in Some Parts of the Eastern Niger Delta Basin

An analysis of Geothermal Gradients in the Eastern Niger Delta basin was done using Bore Hole Temperature (BHT) data from three (3) adjacent oil fields. BHT data was converted to static formation temperature by using the conventional method of increasing measured BHT data by 10% and Geothermal Gradient computed using its simple linear relationship with depth, surface temperature and static temperature at depth. Projections were then made for change in Geothermal gradients at 1km intervals to a depth of 4 km. Results obtained showed significant variations across Idama, Inda and Robertkiri fields with average geothermal gradients of 17.3⁰C/Km, 22.6⁰C/Km and 23.1⁰C/Km respectively. Variation in the geothermal gradients in the area is attributed to lithological control and differential rates of sedimentation during basin evolution. Also, results showed that the Geothermal Gradient in the area are generally moderate and could be a good reason for the occurrence of more oil hydrocarbons than gas in the area.

Supplemental Material: Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico

Information about the sources and processing characteristics of the public seismic, well log, and gas chromatography data; and time-depth conversion parameters, velocity model, and calculations of geothermal gradients.<br>

Supplemental Material: Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico

Information about the sources and processing characteristics of the public seismic, well log, and gas chromatography data; and time-depth conversion parameters, velocity model, and calculations of geothermal gradients.<br>

Geothermal Gradient And Heat Flow Maps Of Offshore Malaysia: Some Updates And Observations

An update of the geothermal gradient and heat flow maps for offshore Malaysia based on oil and gas industry data is long overdue. In this article we present an update based on available data and information compiled from PETRONAS and operator archives. More than 600 new datapoints calculated from bottom-hole temperature (BHT) data from oil and gas wells were added to the compilation, along with 165 datapoints from heat flow probe measurements at the seabed in the deep-water areas off Sarawak and Sabah. The heat flow probe surveys also provided direct measurements of seabed sediment thermal conductivity. For the calculation of heat flows from the BHT-based temperature gradients, empirical relationships between sediment thermal conductivity and burial depth were derived from thermal conductivity measurements of core samples in oil/gas wells (in the Malay Basin) and from ODP and IODP drillholes (as analogues for Sarawak and Sabah basins). The results of this study further enhanced our insights into the similarities and differences between the various basins and their relationships to tectonic settings. The Malay Basin has relatively high geothermal gradients (average ~47 °C/km). Higher gradients in the basin centre are attributed to crustal thinning due to extension. The Sarawak Basin has similar above-average geothermal gradients (~45 °C/km), whereas the Baram Delta area and the Sabah Shelf have considerably lower gradients (~29 to ~34 °C/km). These differences are attributed to the underlying tectonic settings; the Sarawak Shelf, like the Malay Basin, is underlain by an extensional terrane, whereas the Sabah Basin and Baram Delta east of the West Baram Line are underlain by a former collisional margin (between Dangerous Grounds rifted terrane and Sabah). The deep-water areas off Sarawak and Sabah (North Luconia and Sabah Platform) show relatively high geothermal gradients overall, averaging 80 °C/km in North Luconia and 87 °C/km in the Sabah Platform. The higher heat flows in the deep-water areas are consistent with the region being underlain by extended continental terrane of the South China Sea margin. From the thermal conductivity models established in this study, the average heat flows are: Malay Basin (92 mW/m2), Sarawak Shelf (95 mW/m2) and Sabah Shelf (79 mW/m2). In addition, the average heat flows for the deep-water areas are as follows: Sabah deep-water fold-thrust belt (66 mW/m2), Sabah Trough (42 mW/m2), Sabah Platform (63 mW/m2) and North Luconia (60 mW/m2).

Evaluation of geothermal energy resources in parts of southeastern sedimentary basin, Nigeria

Residual aeromagnetic data of parts of Southeastern Nigerian sedimentary basin were reduced to the equator and subjected to magnetic vector inversion and spectral analysis. Average depths of source ensembles from spectral analysis were used to compute depth to magnetic tops (Z), base of the magnetic layer (Curie Point t Depth (CPD)), and estimate geothermal gradient and heat flow required for the evaluation of the geothermal resources of the study area. Results from spectral analysis showed depths to the top of the magnetic source ranging between 0.45 km and 1.90 km; centroid depths of 4 km - 7.87 km and CPD of between 6.15 km and 14.19 km. The CPD were used to estimate geothermal gradients which ranged from 20.3°C/km to 50.0°C/km 2 2 and corresponding heat flow values of 34.9 mW/m to 105 mW/m , utilizing an average thermal conductivity -1 -1 of 2.15 Wm k . Ezzagu (Ogboji), Amanator-Isu, Azuinyaba, Nkalagu, Amagunze, Nta-Nselle, Nnam, Akorfornor environs are situated within regions of high geothermal gradients (>38°C/Km) with models delineated beneath these regions using 3D Magnetic Vector Inversion, having dominant NW-SE and NE-SW trends at shallow and greater depths of <1km to >7 km bsl. Based on VES and 2D imaging models the geothermal system in Alok can be classified as Hot Dry Rock (HDR) type, which may likely have emanated from fracture systems. There is prospect for the development of geothermal energy in the study area. Keywords: Airborne Magnetics, Magnetic Vector Inversion, Geothermal Gradient, Heat Flow, Curie Point Depth, Geothermal Energy.

Thermomechanical Controls on the Timing of Magma Reservoir Failure in a Viscoelastic Crust

&lt;p&gt;As volcanic systems undergo unrest, understanding the conditions required for reservoir failure, the associated timescales, and the links to geophysical observations are critical when evaluating the potential for eruption. The characteristics and dynamics of a pressurised magmatic system can be inferred from episodes of surface deformation, but this process is heavily reliant on the assumed crustal rheology. In volcanic regions, shallow or long-lived magmatic systems can significantly perturb the regional geothermal gradient, altering the rheology of the surrounding crustal rock. Viscoelasticity incorporates a time-dependent viscous deformation response, accounting for the increased ductility and thermomechanical heterogeneity induced by the modelled reservoir.&lt;/p&gt;&lt;p&gt;Here, we investigate the influence of an imposed thermal regime on the critical reservoir overpressure (OPc) required to facilitate failure in elastic and viscoelastic models, alongside the predicted critical surface uplift (Uc). By evaluating tensile and Mohr-Coulomb failure criteria on the reservoir walls, we can determine the mechanical stability of the magma reservoir and identify the conditions that are susceptible to failure. We explore a range of reservoir temperatures (representing felsic, intermediate, and mafic magma compositions) and background geothermal gradients, to simulate varied volcanic regions, and use the Standard Linear Solid viscoelastic rheology together with a temperature-dependent viscosity structure, calculated from the thermal constraints. The models incorporate mechanical heterogeneity in the form of a temperature-dependent Young&amp;#8217;s modulus, accounting for the thermal weakening of the surrounding crustal rock. We use an overpressure rate of 10 MPa yr&lt;sup&gt;-1&lt;/sup&gt;, in excess of lithostatic pressure, that produces an average elastic volumetric strain rate of ~3-7x10&lt;sup&gt;-12&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, depending on the imposed thermal regime.&lt;/p&gt;&lt;p&gt;We show that reservoir failure is systematically inhibited by incorporating viscoelasticity, with OPc for Mohr-Coulomb failure increasing by up to 65% with respect to the corresponding elastic model. The greatest increases in OPc, and Uc, are observed when pairing cool reservoir temperatures (i.e., felsic composition) with low background geothermal gradients. In contrast, stress partitioning due to the viscoelastic crustal rheology promotes failure at the ground surface, decreasing the required OPc for tensile failure by up to 32%. The greatest reductions in OPc are produced in models that couple a hot reservoir temperature (i.e., mafic composition) with low background geothermal gradients. By resisting mechanical failure on the reservoir wall, temperature-dependent viscoelasticity impacts the conditions required for dyke nucleation and propagation. Further to this, a viscoelastic crustal rheology dramatically reduces the timescales for throughgoing failure; complete brittle failure connecting the reservoir to the ground surface. This occurs much earlier than suggested by elastic models, which could have implications for interpreting the conditions, and onset, of a potential eruption.&lt;/p&gt;

Curie depth and heat flow analysis of Ikot Ekpene and environs, Eastern Niger Delta Basin, using airborne magnetic data

Aeromagnetic dataset over Ikot Ekpene and environs, Eastern Niger Delta Basin, was processed to compute the basement depth, Curie isotherm depth, geothermal gradient and heat flow within the area in order to investigate the depth to magnetic sources, geothermal prospect and the hydrocarbon potential of the place. The adopted computational method transformed the spatial data into frequency domain and provided a relationship between radially average power spectrum of the magnetic anomalies and the depths to respective sources. The results of the analysis showed that the depths to centroids and top boundaries range from 7.84 to 13.38 km and 0.233 to 0.459 km respectively. Curie depths within the basin undulate and vary between 15.42 and 26.49 km. The geothermal gradients range between 20.758 and 35.649 ⁰C/km while the corresponding heat flow is about 51.896 mWm⁻² within east of Ikono, north of Mbak and west of Abak Areas and 89.124 mWm⁻² within Amawum, Ndoro, Isiala, Ogbuebule and east of Uyo Areas. Based on the computed sedimentary thicknesses, high geothermal gradients and delineated major faults and fractures which could serve as migratory pathway for hydrocarbon or hydrothermal fluid, some parts of the study area have been demarcated for geothermal prospect and detail hydrocarbon exploration.