ГЕОТЕРМИЧЕСКАЯ МОДЕЛЬ НЕФТЕГАЗОНОСНЫХ ОТЛОЖЕНИЙ ВИЛЮЙСКОЙ ГЕМИСИНЕКЛИЗЫ

Curie point depth and heat flow from spectral analysis of aeromagnetic data over the northern part of Western Desert, Egypt

Recorded maximum bottom-hole temperatures may vary significantly from true formation temperatures because of the effects of drilling fluid circulation. A theoretical temperature correction technique was applied to log-heading data to compute 191 static temperatures for 64 wells on the Scotian Shelf. A linear regression, performed on 140 computed temperatures, produced an average geothermal gradient of 2.66 °C/100 m; correlation coefficient 0.97. A geothermal gradient map constructed from the corrected data shows that areas of thicker sediment accumulation are marked by high geothermal gradients (e.g., Abenaki, Sable subbasins), whereas areas of shallow basement coincide with low gradients (e.g., LaHave Platform, Canso Ridge).It is proposed that the major control on the distribution of Scotian Shelf geothermal gradients is the thermal conductivity of the sediments. Radiogenic heat production within the sediments and subsurface fluid movement probably contribute to a lesser extent. Within the basins, higher heat flow due to thick salt accumulations at depth and the overall low conductivity of sediments above the salt lead to higher geothermal gradients. Low geothermal gradients in shallow basement areas are caused by the lack of salt and the relatively high conductivity of overlying sediments.A technique for calculating maturation levels of organic matter based on Lopatin's method and corrected bottom-hole temperatures was developed for the Scotian Shelf. A geologic model is constructed by considering the burial history of sediment for time invariant heat flow. From this, TTI (time–temperature index) values are derived to give the maturity level for specific sedimentary horizons. A comparison of 106 calculated TTI values with vitrinite reflectance measurements for 15 wells established a calibration of this technique for the Scotian Shelf. A correlation coefficient of 0.95 was obtained for the relation log TTI = 6.1841 log R0 + 2.6557.Maps showing the depth to calculated vitrinite reflectance values of 0.60 and 0.70% were constructed for the Scotian Shelf. It appears that burial rate, in addition to temperature, controls the location of various maturation levels. As one moves seaward, younger sediments increase in maturity and the oil window thickens. At equivalent depths, sediments at the basin margins are more mature than those farther seaward in the deeper parts of the basin. Sediments of the Canso Ridge area and over much of the LaHave Platform, excluding local downfaulted basins, have not attained sufficient maturity to have generated significant quantities of oil.TTI calibrations were established for the Labrador Shelf, the Grand Banks of Newfoundland, and the Canning Basin of Western Australia as above. Results indicate that tectonic history plays an important role in the calibration and that the slope of calibration lines may represent the departure from true time–temperature conditions in the modeling. Changes in heat flow with time lead to incorrect estimates of maturity when present-day geothermal gradients are used to approximate past temperature conditions. Also, uncertainties in the amount of erosion produce error in maturity estimates. The Scotian Shelf TTI calibration may be applicable to much of offshore eastern North America and parts of offshore western Europe and Africa.

SUMMARY Terrestrial heat flow plays a vital role in determining the present thermal regimes of sedimentary basins, offering a robust foundation for understanding hydrocarbon maturation processes and the geothermal resource potential. The Junggar basin is one of the largest and most petroliferous superimposed petroleum basins in China. However, research on heat flow is scarce. In this study, 94 new high-quality heat flow values are derived from through borehole temperature analysis and thermal conductivity measurements of rocks. The results indicate that (1) the geothermal gradient in the basin varies from 11.4 to 28.3 °C km−1, with a mean value of 20.9 ± 3.4 °C km−1, and the heat flow varies from 23.4 to 64.5 mW m−2, with a mean value of 45.1 ± 8.4 mW m−2. The overall low geothermal gradient and heat flow are attributed to the continuous cooling during the Meso-Cenozoic. (2) At basin scale, the high heat flow values are primarily concentrated in areas characterized by basement uplift, whereas the low heat flow values are mainly located in the depressions. This suggests that thermal refraction is the primary factor influencing the heat flow variations. (3) Although large-scale development and utilization of geothermal resources face challenges, certain local areas in the basin show promise for geothermal resource utilization.

An integrated study of the Chad Basin Nigeria has been carried out using heat flow, Bouguer gravity anomaly, depth to basement maps and interpreted seismic reflection data of the area. The seismic reflection data show two main structural elements: faults and folds whose primary structural orientation is northeast–southwest. Other features such as grabens and horst which are formed as a result of tensional stress and magnetic intrusive are also identified in the sections. The Bouger gravity anomaly ranges from −10 to −50 mgal with a northeast to southwest trend while the heat flow values ranges from 63.63 to 105.4 m Wm−2 with an average of 80.6 m Wm−2. The result shows that areas with relatively low heat flux in the southwest and northeast is associated with Bouguer gravity values ranging from −30 to −50 mgal. These parts of the basin also have a higher depth to basement and are associated with low sediment, buried hills and crest of folds. The range of heat flow values computed for this study shows that the basin sediments are thermally mature and therefore has high prospects for oil and gas generation. The graben in the basin is associated with low heat flow and very low negative Bouguer gravity anomaly. The study reveals that a decrease in heat flow is observed with an increasing sedimentary thickness. Thus, by studying the heat flow map, regions of gravity highs and lows can be identified within the Chad basin. Moreover, areas of gravity lows have greater thickness of sediments than areas of gravity highs. Low geothermal gradient causes the formation of oil to begin at fairly deep subsurface levels, but makes the oil window to be quite broad. The heat flow, Bouguer gravity values and seismically determined structural features suggest that the Chad Basin Nigeria has good prospects for hydrocarbon plays in Cretaceous rocks, with high potentials for both structural and stratigraphic traps. The southwestern and northeastern axis of the basin is therefore recommended for further drilling to deeper depth based on the results of this study.

This study presents the result of the estimation of heat flow from six (6) wells (Well X:001 to 006) in South-Western Niger Delta using values of Geothermal gradient (GG), Geothermal heat flux (Q) and thermal conductivity (K) computed from Sonic and continuous temperature log data for each well. Geothermal gradient was computed from continuous temperature logs using the simple gradient method while geothermal heat flux and thermal conductivity of the rocks in the wells were computed from the sonic log data, using the Relative Heat Flow Model and Fourier One-dimensional Heat Flow Law respectively. The results were analysed and interpreted to investigate the thermal structure and pattern of heat flow distribution of the basin. Results showed that geothermal gradient ranges from 1.45 0 C/100m to a value of 1.61 0 C/100m, with a simple average of 1.55 0 C/100m. Geothermal gradient contour map computed from this result, showed a low thermal gradient at the northern part of the study area where we have Well X-006 and increases outwards in all direction as we move further offshore. These differences reflect changes in thermal conductivity of rocks, ground water movement and endothermic reaction during diagenesis, since geothermal gradient is influenced by lithology or differential rate of sedimentation. Therefore, it was inferred that sediments with a relatively high geothermal gradient (1.55 to 1.61 0 C/100m) will mature earlier (low oil window) than those with low thermal gradient values. By implication, a high geothermal gradient enhances the early formation of oil at relatively shallow burial depths, but causes the depth range of the oil window to be narrow, while low geothermal gradient causes the first formation of oil to begin at fairly deep subsurface levels, but makes the oil window broad. Geothermal heat flux estimated from subsurface temperature and one-way sound travel time, shows heat flux varying between 33.16 mWm -2 to 72.73 mWm -2 with a simple average of 48.43 mWm -2 . Low heat flux was observed at the central part of the study area which increases towards the western and eastern parts of the area with Well X-005 characterized by a higher geothermal heat flux. Therefore, it was inferred that the western and eastern parts of the study area with higher heat flux values may be characterized as zones with maximum sediment thickness and are characterized as having depressions (gravity low) on the geoid which is characteristics of a basin, while the central part of the study area with low heat flux values correspond with zones of minimum sediment thickness. Also, thermal conductivity of rocks in the study area computed directly from heat flux and geothermal gradient results, ranges from 2.28W/m 0 C to 4.76 W/m 0 C with an average of 3.19 W/m 0 C. Thermal conductivity contour map computed from this result, showed low thermal conductivity values observed at the central part of the study area, and increases outwards towards the west and eastern parts. This pattern of thermal conductivity variation suggests probably there exists heavy crude oil at the central part of the study area and lighter crude oil as we move outward in all direction. It was also observed that within each well, thermal conductivity increased with depth and decreased with porosity which may be caused by difference in lithology and fluid content, due to the fact that all pore fillers (i:e gases and liquids) are poor conductors. The estimated values of geothermal gradient, heat flux and thermal conductivity obtained in this study are similar to the results obtained from previous studies in the region and with other passive continental margins of the world. Keywords: Heat flow, Geothermal Gradient, Geothermal Heat Flux, Thermal Conductivity, Continuous Temperature and Sonic log. DOI: 10.7176/JETP/10-2-04 Publication date: April 30 th 2020

The Karacadag Volcanic Complex (KVC) is the largest volcanic unit in SE Turkey. It is also defined as a shield volcano on the northernmost part of the Arabian Plate. The main goal of this study is to investigate the geothermal potential of this region associated with the magnetic signature of this volcanic complex and surrounding area. Besides this primary objective, the possibility of there being volcanic intrusion into the buried fault zones under the volcanic cover are also investigated to determine the interrelations between the active tectonics and heat flow in the area. A spectral analysis method is applied to the magnetic anomalies of the volcanic rocks to identify the Curie point depth (CPD) and geothermal gradient, as well as to estimate heat flow and radiogenic heat production of radioactive minerals in the complex. A tilt angle map is also presented, in correlation with instrumentally recorded earthquake magnitudes, to indicate tectonic trends that are consistent with the maps of the thermal parameters in this study. In contrast with expectations for the KVC area, the region around Akcakale and Suruc Grabens is the most prolific zone for geothermal potential, despite them not showing strong magnetic anomalies. Curie point depths are shallow, down to 18 km, around the Akcakale Graben, and deeper, down to 22 km, around the Bitlis-Zagros Suture Zone where the geothermal gradients increase from 26 to 32 °C km−1 through the graben area. Heat flows in this zone are in the range from 75 to 90 mW m−2 depending on the thermal conductivity coefficient (2.3, 2.5, 2.7, and 3.0 W m−1 K−1) used. Radiogenic heat production values also indicate slightly changing spectra in the range 0.19 to 0.25 μW m−3). None of these parameters are focused around Mt. Karacadag. However, the earthquake epicenters (generally M ≤ 4) are aligned with the boundary faults of the Akcakale Graben where the CPD, geothermal gradient, and heat flow maps indicate relatively high potential. We thus suggest that this graben area would be good for future geothermal exploration. On the contrary, considering the low geothermal gradient and heat flow values, Mt. Karacadag can be accepted as being an extinct volcano, despite its apparent, high, magnetic anomalies.

Terrestrial heat flow in the Malawi Rifted Zone, East Africa: Implications for tectono-thermal inheritance in continental rift basins

Heat flow and gas hydrate saturation estimates from Andaman Sea, India

The distribution of gas hydrate on a continental slope is often characterized as a wedge that pinches out on the seafloor. This part of the hydrate stability zone is particularly relevant for studies of the dynamics of hydrate accumulations, such as processes related to slope stability or hydrate dissociation leading to methane release into the overlying ocean. For regions with very low geothermal gradients, we have produced a series of thermobaric models of the shallow hydrate stability zone that contain an unexpected geometrical distribution of hydrated sediments. In these models, the shallowest part of the stability field thickens and bulges landward. Such a feature is more likely to happen in regions where low geothermal gradients are further lowered by high sedimentation rates. Also, the effect is greater beneath colder oceans. Although a hydrate stability zone bulge would be difficult to image with conventional seismic methods, there are numerous locations around the world where such a system could develop.

A wide, systematic variation of sedimentary geothermal gradients has been previously observed along the northern continental shelf of the Gulf of Mexico. From east to west, geothermal gradients change from 25 to 30 °C/km off Alabama to lower values (15–25 °C/km) off eastern Louisiana and to higher values (30–60 °C/km) off Texas. In order to assess the mechanism responsible for this variation, the present study first compiled an extensive bottom-hole temperature database from over 6000 wells in the northern continental shelf and constructed a more detailed geothermal gradient map than those published previously. Second, basin models were then constructed for three areas within the continental shelf (off Texas, Louisiana, and Alabama) that show differing geothermal gradients. A basin model is a mathematical model that simulates the heat transport through the crust and the sediments of a basin in the context of its geologic evolution. Previous researchers proposed two possible causes for the observed geothermal gradient variation in the northern continental shelf. The first was the thermal effect of sedimentation: areas with faster sediment accumulation result in low geothermal gradients, and vice versa. The second was that basal heat flow (heat flow that enters from the igneous crust to the bottom of the sediments) varied across the continental shelf. The present study finds that sedimentary geothermal gradients in these areas are primarily impacted by two competing mechanisms associated with sediment accumulation. One is the radiogenic heat production within the sediment that adds to the total heat budget upward through the sedimentary column. The other is the transient effect of fast sediment accumulation, which results in reduction in the upward heat flow. Off Louisiana, the transient effect prevails, and hence the area shows the lowest geothermal gradients. Off Texas, due to slower sedimentation, the positive contribution by radiogenic heat is most significant. Off Alabama, because the sediments there are not as thick, the overall contribution of radiogenic heat is less. The models show that the thermal effects of sedimentation are large enough to explain the observed variation in geothermal gradients. Therefore, corresponding variation in basal heat flow is not required.

Local ground-water temperatures and bottom-hole temperatures for oil and gas wells present two lines of evidence indicating regional high geothermal anomalies along the Balcones-Ouachita trend in central Texas. Analysis of the variables in the heat-flow equation, however, indicates that these anomalies are probably not due to conductive heat flow; most of the rock units for which data exist are limestones and sandstones, and thus, should have high thermal conductivities and low geothermal gradients. Measurements of heat flow are few along this trend, but because the strata for which bottom-hole temperature data exist generally contain fluids, it is reasonable to assume that hydrodynamics also is a factor in creating these apparent thermal anomalies. In short, Darcy's law, not the heat-flow equation, may control thermal conditions: rocks having high thermal conductivities generally also have high hydraulic conductivities, so upwelling warm waters may account for the observed thermal anomalies. Since upwelling waters also may be important conveyors of hydrocarbons, these geothermal and/or hydrodynamic anomalies also indicate promising areas for petroleum exploration. Detailed investigations, however, demonstrate that these regional anomalies have high-frequency perturbations; local areas within a regional high may have anomalously low temperatures. Local faulting not discernible on a regional scale may control detailed hydrodynamic conditions, and in effect, these faults may form structural traps for hydrothermal fluids as well as for hydrocarbons. However, they can also localize downwelling recharging waters that impart a low thermal anomaly. Clearly, a radius of influence exists within which any well senses the ambient thermal regime. Within a fault zone, this radius is probably small, dictated by detailed stratigraphic dislocations. Although complex perturbations affect the prevailing thermal regime in ways not yet completely understood, some of these geothermal anomalies indicate general loci of long-term upwelling from deep within the Gulf Coast basin. Studied in detail, thermal anomalies may prove to be indicators of economic geothermal resources. They also may indicate hydrodynamic traps, in which warm waters might have filtered through a trap zone during the process of petroleum accumulation. In this way, these thermal anomalies may point toward hydrocarbons in a downstructure direction. End_of_Article - Last_Page 1431------------

The Malita Graben is located in the northern Bonaparte Basin, between the Sahul Platform to the northwest and the Petrel Sub-basin and Darwin Shelf to the south. The wells Beluga 1, Heron 1, Evans Shoal 1, Evans Shoal 2 and Seismic Line N11805 are selected to determine the thermal history and potential of hydrocarbon generated from the Plover, Elang, Frigate Shale (Cleia and Flamingo), and Echuca Shoals formations source rocks. The modeling was performed by using Basin Mod 1-D and 2-D techniques. The model results show that the geothermal gradients range from 3.05 to 4.05°C/100 m with an average of 3.75°C/100 m and present day heat flow values from 46.23 to 61.99 mW/m2 with an average of 56.29 mW/m2. The highest geothermal gradient and present-day heat flow values occurred on a terrace north of the Malita Graben. These most likely indicate that hot fluids are currently variably migrating into this structure. The lower geothermal gradient and heat flow values have been modeled in the southeast sites in the well Beluga 1. The northern Bonaparte Basin experienced several deformation phases including lithospheric thinning; hence, heat flow is expected to vary over the geological history of the basin. The higher paleo-heat flow values changing from 83.54 to 112.01 mW/m2 with an average of 101.71 mW/m2 during Jurassic rift event (syn-rift) were sufficient for source rocks maturation and hydrocarbon generation during Cretaceous post-breakup sequence (post-rift) in the study area. The Tuatara (Upper Frigate Shale) Formation source rock with type II & III kerogen dominantly showing mixed oil- and gas-prone, and Plover Formation with type III and gas prone have never reached the peak mature oil window in the well Beluga 1. This area indicates that the maturity of source rocks is low and considered to be from poor-to-good organic richness with poor-to-fair potential for hydrocarbons generation. The post mature Cleia (Lower Frigate Shale) and Echuca Shoals formations source rocks in the well Evans Shoal 1 and an early mature oil window Echuca Shoals formation source rock in the well Evans Shoal 2, characterized by type III kerogen dominantly showing gasprone are a fair-to-very good source richness with poor potential for hydrocarbons generation. The low to high maturity of Echuca Shoals and Petrel (Frigate Shale) formations source rocks in the well Heron 1, Plover Formation source rock in the Evans Shoal 1 well, and Cleia (Lower Frigate Shale) and Plover formations in the well Evans Shoal 2, showing gas-prone with type III and II & III kerogens predominantly, have reached the late mature oil and wet gas generation stages at present day. These last five formations source rocks are seen from poor-to-very good organic richness with poor-to-very good potential for hydrocarbons generation in the Malita Graben.

Examination of conodont colour alteration (CAI) in samples from more than 40 petroleum exploration wells and extensive outcrop collections along the northern margin of the Lennard Shelf forms the basis for a study of the thermal maturation and geothermal history of the Canning Basin of Western Australia. The thickness of the measured CAI intervals is variable and does not conform to the 1200 m standard of the Appalachian Basin. The CAI interval 1 is thick and indicates a low geothermal gradient in the basin but CAI intervals 1.5 and 2 are thin and indicate higher geothermal gradients. A major thermal event of Miocene Age, associated with the intrusion of the Fltzroy Lamproites in the Fitzroy Graben and Lennard Shelf, may be the source of the increased heat flow and also explain an area of high heat flow in some parts of the Graben and shelf.Using the vertical and horizontal distribution of trends of the CAI intervals it is suggested that over large areas of the basin the oil generation window is restricted to an interval about 1100 m thick and, except where migration has taken place, that liquid hydrocarbons will be restricted to the interval between 1600 and 3000 m. In areas affected by the intrusion of the Fitzroy Lamproites, the top of the oil generation window may be as shallow as 800 m.

The Curie depths of the United Arab Emirates: Implications for regional thermal structures and tectonic terranes

Geothermal energy, as a renewable and green source for power generation and district heating and/or cooling, is available all year round, at all times of the day, and has great potential for development in any country. However, the exploitation of deep geothermal resources is only possible after detailed characterization of the potential reservoir. In fact, knowledge of the thermo-physical properties of the underground reservoir is crucial for generate a forecast  estimation of the geothermal reservoir thermodynamic behavior, as well as for mining risk reduction and optimization of the sound design of geothermal energy production systems.The InGEO project (Innovation in GEOthermal resources and reserves potential assessment for the decarbonisation of power/thermal sectors) aims to develop an innovative exploration workflow integrating geophysical data and other direct and indirect information, organized to make available a sort of decision support system of geothermal projects. It consists of the reconstruction of the crustal and subcrustal structures by joint analyses and interpretations of available and acquired geological and geophysical data (e.g., those provided by mechanical and thermal rock samples laboratory analyses, seismic and gravity anomalies), taking advantage of the different sensitivity that geophysical methods have on physical rock's parameters (temperature and composition). The results will be the input for the geothermal model that will quantify the deep geothermal resource potential of the area. The designed workflow will be tested in a case study area and partially calibrated with developed (hydrothermal) available data. The methodological approach proposed by InGEO is also expected to define the potential local use of geothermal systems by Deep Closed-loop Borehole Heat Exchangers (DBHE) for power generation, district heating and/or cooling. The InGEO results will contribute to the second mission of PNRR “MISSION 2: GREEN REVOLUTION AND ECOLOGICAL TRANSITION”, by expanding the business planning of deep geothermal resource use in Italy.The test area, chosen because it is considered particularly representative of the project topic and of potential reproducibility, includes the sector of the Northern Apennine buried structures, belonging to the Romagna and Ferrara Folds (RFF). The RFF area has been the target of previous geothermal studies highlighting relatively low geothermal gradients within the deep carbonate units (on average 14 °C/km) and more significant thermal gradients (on average 53 °C/km) in the overlying impermeable formations [1-2]. This feature in temperature distribution with depth is clear evidence for fluid thermal convection occurring in the deep-seated carbonate units of Mesozoic age, which constitutes the local geothermal reservoir.[1] Pasquale et al., 2013. Evidence for thermal convection in the deep carbonate aquifer of the eastern sector of the Po Plain Italy. Tectonophysics, 594, 1-12.[2] Pasquale et al., 2014. Heat flow and geothermal resources in northern Italy. Ren. Sust. Energy Rev., 36, 277-285.