Regional-residual Separation Research Articles

Interpretation of gravity data to delineate the subsurface structures and reservoir geometry of the Aluto–Langano geothermal field, Ethiopia

The Aluto–Langano geothermal field is located within the central-southern part of the Main Ethiopian Rift, about 200 km southeast of Addis Ababa. This study analyzes gravity data to define the geometry of the geothermal reservoir and subsurface geological structures controlling the geothermal system. A Bouguer anomaly map of the area was generated using a Bouguer density of 2.49 g/cm3, which was obtained from the gravity dataset using different optimization methods. In order to highlight the structures of interest in the calderic system, a regional-residual separation was conducted. The map produced shows two dominant high Bouguer anomalies underlying Aluto caldera associated with the presence of basaltic rocks and the occurrence of fumarolic activity. Analysis of horizontal gradients of gravity data showed that the area is characterized by the presence of high gradient anomalies associated with geothermal manifestations. A 3-D gravity model for assessing the geothermal heat source architecture within the Aluto caldera area is also presented. The model was constrained using the estimated densities of rock cuttings obtained from drilled wells. The results from 3-D modeling imaged a high-density body at depth surrounded by a less-dense body (∼2.55 g/cm3), which is interpreted to be the geothermal reservoir. The model was then interpreted together with surface manifestations, lithology, and geological structures. The less-dense body found west of the Adonsha fault lineament could be the expression of the second reservoir, which is likely deeper than the productive reservoir found along the NNE–SSW trending structure (i.e., the Artu Jawe Fault Zone) in the central area.

Tectonostratigraphic evolution of the new frontier Foram Basin and implications for hydrocarbon potential, Western Desert, Egypt

The Western Desert of Egypt is an important hydrocarbon province as it consists of many petroliferous sedimentary basins. The researchers and petroleum companies are interested in exploring the new frontier sedimentary basins and evaluating their hydrocarbon potential. Given this point of view, the current study attempts to assess the new frontier sedimentary basin in the Western Desert of Egypt, named Foram Basin (FB), using various geophysical and geological methods, including the magnetic, gravity, and seismic methods in addition to the petroleum system and basin analysis modeling. The magnetic data analysis uses various techniques, including power spectrum and source parameter image, total magnetic intensity (TMI), reduction to the pole (RTP), regional-residual separation, and tilt derivative. The used techniques in the interpretation of gravity data include Bouguer gravity, power spectrum, regional-residual separation of Bouguer gravity, tilt derivative of the Bouguer gravity and gravity inversion, and 2D gravity modeling, in addition to the tentative basement depth based on the gravity inversion and 2D gravity modeling for the nine profiles. The main results of these techniques indicate that the main structural trend is NE-SW and the depth to the basement ranges from 1.8 to 5 km comprising two depocenters.Two-thirds of the sedimentary basin fill is a Paleozoic succession and one-third is a Mesozoic-Cenozoic succession. Therefore, the FB is thought to be a Paleozoic basin. The Paleozoic-Mesozoic stratigraphic framework of the FB was classified into six seismic sequences separated by the seven seismic boundaries. The main regional structural trend of the FB is NE-SW, the same trend as that of the Paleozoic Kufra Basin in Libya. In the FB, the major structural trend in the Early Paleozoic is NE-SW, whereas it is E-W in Late Paleozoic. Moreover, in Mesozoic Jurassic time, the dominant trends are E-W and ENE-WSW, and in Middle Cretaceous is ENE-WSW and in Upper Cretaceous are E-W and NE-SW. Regarding the tectonic subsidence rate, the FB passed three tectonic phases. The first tectonic phase has a high subsidence rate that occurred in the Paleozoic, resulting in the deposition of most of the sedimentary succession. The second and third tectonic phases occurred at a relatively low subsidence rate, resulting in the deposition of Mesozoic-Cenozoic deposits. The Paleozoic Silurian Kohla source rock passed the early generation phase in the Early Eocene (50 Ma) and reached a maximum generation rate of 2.77 (mg/gTOC^my) in Late Oligocene (27 Ma) that is considered a very low rate and did not allow for oil expulsion.

Separation of geomagnetic anomalies in the Bashmaq area in northwestern Iran by factorial kriging

Geomagnetic measurements detect the superposition of both regional and residual anomalies. Regional anomalies are caused by deep geological structures, while the residual ones are due to shallow sources. The presence of regional anomalies complicates the interpretation of magnetic data; to this end, a variety of techniques have been proposed for regional-residual anomaly separation. Most of them are based on Fourier transforms. Although valid results can be obtained from these methods, they have some limitations, such as requiring basic knowledge on approximate cut-off frequencies. This study focuses on spatial filtering employing factorial kriging (FK) for geomagnetic anomaly separation. FK employs geostatistical filtering based on spatial dependencies of the data. In contrast to the upward continuation, which is a trial and error method and needs to be checked with different distances of continuations, the utilisation of FK on synthetic data revealed that FK could automatically perform the separation and also helps to find the optimum distance for the upward continuation method. Following experiments with a synthetic model, the method was applied to real magnetic data of Bashmaq in northwestern Iran. Applying FK on a complicated real case study showed that it could separate the regional and residual components satisfactorily. Furthermore, results from the proposed approach have been compared against the Gaussian Separation Method (GSM). The results are compared to borehole information. The lithological columns are presented as part of the geology investigation. As demonstrated in the case study, the FK method has proven to be an accurate tool to better determine the mineralisation zones compared to GSM, which, in turn, facilitates the interpretation.

2D modelling of high resolution aeromagnetic data over northern sector of Bida basin north-central Nigeria

The study was carried out in the northern sector of Bida basin. The study focuses on mapping depths to magnetic basement and basement structural framework that may assist in delineating overlying sedimentary sections that have prospect for hydrocarbon exploration. High resolution aeromagnetic data of the study area was subjected to regional residual separation, analytic signal and 2D modeling using Oasis Montaj geo-software. Results of the analytic signal demarcated the basement/sedimentary contact, interpretation of 2D geologic models revealed a horst and graben structures underlying the sedimentary formations in the northern sector of Bida basin. The graben structures having sedimentary fills to a depth greater than 2 km were viewed as favourable sites for source rock development. In view of the aforementioned areas around Bakoni, northeast of Tshipo, Enagi and southwest of Wuya with thick sedimentary piles were recommended for further application of other geophysical methods of better resolving power to explore the area for hydrocarbon; since the basin has potentials for hydrocarbon generation.

Identification of Cameroon's geological structures through a gravity separation and using seismic crustal models

Residual gravity data provide useful information for a geophysical interpretation of geological sources. Several techniques have been developed and applied to separate a different content in gravity data. Nevertheless, few methods actually incorporate factual geophysical or geological information in gravity data processing. Instead, most of these methods relay only on mathematical techniques that do not necessarily reflect the actual geological composition and problems inherent to gravity inversion, most notably a non-uniqueness of solutions to gravimetric inverse problems (i.e. infinity many geological configurations could theoretically provide the same gravity solution) as well as the fact that gravimetric inverse solutions are generally ill-posed problems that require employment of regularization techniques. To partially address this issue, we apply a gravimetric forward modelling based on available seismic crustal structure models to separate a residual gravity signal from observed gravity data in order to interpret more realistically detailed geological and tectonic features. This procedure involves the estimation of the uppermost mantle gravity contribution that is treated as a regional gravity data. The residual gravity data is then obtained by subtracting the regional gravity data from observed gravity data. In addition, observed gravity data are typically corrected for the gravitational contributions of topography and bathymetry (and possibly other known crustal density heterogeneities, such as sediments and density variations within the underlying consolidated crust). The application of these gravity corrections to observed (free-air) gravity data yields the Bouguer gravity data. We employ this forward modelling approach to the Bouguer gravity disturbances over Cameroon. Furthermore, we apply a regional-residual separation based on a spectral analysis and a robust polynomial fitting. The performance of these three techniques is compared in terms of their interpretational quality. The numerical analysis reveals that the residual gravity disturbance map obtained by applying the forward modelling technique resembles main known geological and tectonic configuration and closely reproduces even more detailed features. The results from using a spectral analysis could to some extent reproduce realistically tectonic and geological structures, except for more localized features otherwise seen in the forward modelling result. A robust polynomial fitting, on the other hand, fails to provide residual gravity disturbances that realistically reflect geological and tectonic configuration of the study area. The reason is that this method produces either only positive or only negative gravity disturbances, but not both. Moreover, this merely mathematical technique does not take into consideration available geological and geophysical information.

Quaternary Alluvial Aquifer Study Using Integrated Geophysical Approach in Zaghouan Plain (Northeastern Tunisia)

The study area Zaghouan Plain (northeastern Tunisia) is unique for its strategic Quaternary aquifer, which is, in a great proportion, composed of sand lenses that vary in thicknesses and forms. Conducting an integrative approach based on regional mapping and local studies helped provide precise calibration to identify convenient areas for hydrogeological explorations, which are focused on heterogeneous alluvial and fluvio-deltaic aquifers. To enhance the location and the extension of low density related to sand lenses porous aquifers, a regional gravity analysis supported by focused seismic interpretation was performed. Thus, advanced analyses were conducted in the Zaghouan Plain through the implementation of a regional–residual separation, a radially averaged power spectrum and tilt/TDX filter density models. During the process, two major negative gravity anomalies, associated with developed lenses system between Zaghouan Mountain and Henchir Bouslim anticline, were revealed. The anomalies differed in direction from E–W to NW–SE. They also varied widthwise from 1000 to 3000 m and depthwise from 1500 to 2000 m. Hence, with the aim of highlighting the detailed geometry of sand lenses and locating the most interesting zone for future hydrogeological exploration and/or recharge process, 1D time-domain electromagnetic and 2D electrical resistivity tomography studies were conducted and various techniques were applied in a local area situated in the main negative gravity anomaly.

Remnant plume head under Neoproterozoic Malani Igneous Suite, western India

The plumbing architecture of the Neoproterozoic Malani Igneous Suite (MIS), representing one of the largest, intraplate, anorogenic rhyolitic volcanism in western Rajasthan, is poorly constrained. We present a crustal scale model from gravity anomaly modelling also supported by other geological and geophysical observations. The regional-residual separation using frequency filtering technique reveals the presence of high-density discreet bodies at different crustal levels. A 2½D forward and 3D constrained inversion of the residual gravity anomaly suggests the presence of sediments covering MIS, and 6–8 km thick high-density sills emplaced in upper crust down to ~9 km depth. The high gravity anomalies in the remaining part of the Bouguer anomaly could be explained by the presence of 10–12 km thick high-density magmatic intrusion at the base of the Moho below 32–38 km depth. These high-density bodies may be attributed to mafic/ultramafic cumulates during MIS magmatism. It appears that the magmatic melts migrated upwards from the mantle to lower crustal magma reservoirs may alter the bulk magma composition by crustal assimilation. The ensuing density contrast would lead to the upward migration of the dominant felsic melt and their emplacement at shallower depths.

Structural fabric over the seismically active Kachchh rift basin, India: insight from world gravity model 2012

The Kachchh rift basin (KRB), located in the western continental margin of India, is very important due to repeated large magnitude occurrence of intraplate earthquakes. The present study elucidates the subsurface structural features using wavelength filtering, total horizontal derivative (THD) and 2.5 dimensional (2.5D) density modelling of the gravity data. Power spectrum analysis of the gravity data gives the cut-off wavelength of 100 km that has been used for wavelength filtering for regional-residual separation. The residual gravity anomaly significantly enhances the shallow features (like Allah-Bund fault, Kachchh mainland uplift, Wagad uplift, and Pachham uplift) and gives an NW–SE subsurface structural trend. The predominant direction for major lineaments derived by the THD of gravity data shows the ENE–WSW as well as NE–SW and NW–SE directions. The 2.5D density model of the regional gravity anomaly reveals the presence of high-density magmatic underplating layer and intrusive mafic body in the lower crust that is in accordance with the previous studies. The regional slope of the Moho in the KRB is towards the SW direction. An intrusive mafic body in the lower crust and volcanic plugs in the upper crust act as stress concentrator which is responsible for seismicity in the KRB. Several new lineaments have been identified based on the present study, which may be accountable for seismicity over the different part of KRB.

Structural Investigation of Udi LGA of Enugu State, South Eastern Nigeria Using High Resolution Bouguer Gravity and Landsat Data

The focus of this study is to investigate the structures peculiar in Udi, Enugu State, Nigeria. This was achieved by delineating the regional from the residual, determining the lateral and sedimentary thicknesses of causative structures with their lateral boundaries and corresponding lineaments. Regional-residual separation was employed on the aerogravity dataset while Georeferencing and creation of new coordinate system was undertaken on the Landsat data. Causative sources with short and long wavelength trending in the NE-SW, NNE-SSW, E-W, WNW-ESE, N-S and NW-SE directions were found to exist within the study area as qualitative analysis was applied on the aerogravity and landsat data. The NE-SW and NW-SE trends are possible oil and gas rich belt within the area. Quantitatively, two depth source models D1 and D2 were identified. D1 depicting depth to deeply seated sources varies from 0.00071 to 0.0044 km with true thickness of 0.01 km. The shallow related sources expressed using D2 lies between 0.0014 to 0.0034 km with true value of 0.0005 km. If other conditions like structural features and depth parameters are met, a true sedimentary thickness of 0.01 km shows that the area will encourage mineral and water exploration rather than hydrocarbon exploration.

A computation scheme based on field attenuation rate for improving regional-residual separation of potential field data set

AbstractTo further improve the accuracy of regional-residual separation of potential field data set, this paper presents a novel computation scheme based on different attenuation rate of the fields induced from deep and shallow sources respectively. For the new scheme, the observations are first upward continued to a plane above it to get an updated field. Then, the difference between the original field and the updated field is calculated. Next, a controlling parameter is set to select those data points whose amplitudes have been much reduced. The adverse effects from the residual anomalies on the fitting of the regional trend can be reduced by removing the identified local points from the original field. Finally, a low-order polynomial is utilised for approximating the regional trend, and the corresponding residual field can be obtained by simple subtraction. Compared with gradient-based methods, the proposed new scheme has better noise adaptability for distinguishing different anomalies. The accuracy of the presented scheme was tested on synthetic data with and without noise. All tests showed that the new scheme reduces subjectivity and inaccuracy of the conventional methods significantly. In addition, the scheme was applied to Bouguer gravity anomaly of the Dida orebodies in Jilin Province, northeast China. This application also verified the superiority of the proposed scheme.

Determination of hydrocarbon potentials in Masu area northeastern Nigeria using forward and inverse modeling of aeromagnetic and aerogravity data

Aeromagnetic and aerogravity data covering Masu area, which lies within latitudes 12°00′ to 13°00′ North and longitudes 12°30′ to 14°00′ East in Nigerian sector of Chad Basin have been interpreted qualitatively and quantitatively. Regional-residual separation was carried out by applying polynomial fitting (first order), which was fitted by least square method. First order was used because it is the best regional fit for our data as it reflected the available geological information of the area. The residual values of both magnetic and Bouguer anomalies obtained were used to produce the residual magnetic intensity and residual gravity maps respectively. These maps show intrusive basement rocks in the eastern part of Masu. The forward and inverse of aeromagnetic data modeling estimated basement depths for profiles P1 and P2 were 4300 and 1195 m, with respective magnetic susceptibility values of 0.0003 and 0.0250, which indicate minerals like limestone and marble. Similarly, the estimated basement depths from the forward and inverse of aerogravity data modeling are 6524 and 4312 m for P1 and P2 with density contrasts of 0.72 and 0.255 g/cm3. The results from this work indicate that the area has some geologic features suitable for hydrocarbon and mineral deposits. Hence, further geophysical researches need to be carried out to ascertain the type of minerals existing in the area.

English

The aeromagnetic data of Otukpo (sheet 270) and Ejekwe (sheet 289) areas of the lower Benue Trough of Nigeria were interpreted quantitatively. The quantitative interpretation employed spectral analysis technique with the aim of locating specific basement depths to buried magnetic source rocks in the study area. First order polynomial fitting was adopted for regional-residual separation of the total magnetic intensity (TMI) map. The result of the spectral analysis indicates two depth source models; with depths to the deep sources varying from 2546.5 to 4177.3 m, having an average depth of 3058 m; while the depths to the shallow magnetic sources vary from 309.4 to 762.5 m, with an average depth of 527 m. The Otukpo area has greater sediment thickness capable of hydrocarbon accumulation than the Ejekwe area. This is supported by the presence of many intrusions at the Ejekwe area, with large lateral extents, indicative of over mature source rocks. Keywords: Aeromagnetic data, spectral analysis, basement depths, hydrocarbon potential.

Using EGM2008 Gravity Data for Mapping and Detecting Structural Subsurface Anomalies in the Mayo-Kani Division (Cameroon)

To resolve the problem of gravity mapping in the Mayo-Kani Division, we extracted a sample of data from the high-resolution Bouguer anomaly database EGM2008. The objective of this process was to map and detect subsurface anomalies in the region. Regional-residual separation was applied to the data using a third-order polynomial fit. This separation enables to obtain regional and residual maps. Other filtering actions, such as horizontal and vertical derivatives, have been applied to the data to enhance sources of anomalies in the study area. The residual map of the study area was superimposed on the geological map to delineate and interpret the correlation with the shallow geological structures. The main sources of residual gravity anomalies have been recognized. The interpretation of the derived maps revealed the N-S, E-W, NE-SW and NW-SE structural patterns. These trends have been associated with the major structural directions observed in the Far North Cameroon region. The Euler Deconvolution allowed the detection of sources of anomalies and to determine their depths. The fracture map obtained from this method has improved knowledge on the search for buried ores and the geological structures associated with oil and gas deposits. Overall, the generated gravity maps provided a better understanding of the Mayo-Kani geological setting.

Estimation of Geothermal Gradient and Heat Flow for Determination of Geothermal Energy Sources in Monguno Area of Northeastern Nigeria

The aeromagnetic data of Monguno area northeastern Nigeria have been used to estimate Curie point depth, geothermal gradients and heat flow using spectral analysis. These geothermal parameters were subsequently employed to identify areas of geothermal resources. First order polynomial fitting was applied in Regional-residual separation. The Curie point depth obtained in this area ranges from 10.318 to 24.476 km with an average of 13.387 km, the geothermal gradient of the area varies from 23.697 to 56.212°C /km, with an average of 46.195°C /km, while the heat flow ranges from 59.242 to 136.176 mWm-2, with an average value of about 112.364 mWm-2. It was also observed that the deepest Curie depth in the area is identified in the south, while the shallow depth is located in the northeast and spread toward the southwest. On the other hand, the highest geothermal gradient in the area is identified in the northern part of Moguno, while in the south, the lowest, geothermal gradient is located. The highest heat flow in the area is seen in the south-west and north-east, while the lowest heat flow is observed in the south. The high heat flow and geothermal gradient in the area show that geothermal energy could be found in Monguno region of the northeastern Nigeria.

Geothermal Energy Potential of the Chad Basin, North-Eastern Nigeria

In this research paper, the sub-surface heat flow of a part of the Chad Basin, in North eastern Nigerian was estimated using spectral analysis. This was obtained from twenty (20) digitized High Resolution Aeromagnetic (HRAM) data sheet covering the study area. Regional-residual separation using first order polynomial fitting method with three coefficients was carried out on the data map before the application of statistical spectral analysis. Result shows that the centroid depth varies between 9.39 km and 18.31 km. The depth to the Curie temperature isotherm varies between 15.14 km and 33.46 km below the mean sea level. It was also found that the Curie temperature isotherm within the basin is not a horizontal level surface but an undulating surface with geothermal gradients and heat flow ranging between 15.77 and 38.31°C/Km, and 39.41 and 95.77 mWm -2 respectively. Thus, the calculated average geothermal gradient and heat flow for this area are 23.39°C/Km and 58.47 mWm -2 respectively. Since average heat flow in thermally normal continental region is 60 and the values in excess of 80 mWm -2 – 100 mWm -2 are associated with anomalous geothermal conditions, hence the study area can generally be considered as a thermally normal region. But, the northeastern part of the study area with values in excess of 80 mWm -2 is recommended for further investigation Keywords: Geothermal energy, Spectral Analysis, Chad Basin. Curie point depth

New Insights from Gravity Data on the Geodynamic Evolution of Northern African Passive Margin, Case Study of the Tajerouine Area (Northern Tunisian Atlas)

In Northern Tunisia, geological structuring is very diverse. This diversification is due to its localization, which is situated within the convergence zone between Africa and Eurasia plates. This situation allows to a complicated geodynamic evolution from Permian Tethy’s opening to the quaternary. Our study area is a key zone because we find several structures (Triassic extrusions, reefs, folds, grabens). The Surface studies (structural, sedimentology, etc.) leave controversies and many directions are only indicated as supposed faults. Thus, to understand geodynamic evolution is very important for petroleum and mining exploration. For this purpose geophysical method, which corresponds to a gravity data interpretation, is used to explore the subsurface structures. In this study, different techniques (regionalresidual separation, Horizontal gradient magnitude, upward continuation, Euler DE convolution) were applied to the gravity anomaly map. The results obtained allowed to draw up a structural map showing faults system responsible for structuring the study area. The obtained structural map is consistent with several faults already identified in previous studies and shows new directions. This map leads to better understanding the geological structures and the geodynamic evolution of the region and is a very useful document to guide future mining and hydrocarbons operations research.

Filter assisted bi-dimensional empirical mode decomposition: a hybrid approach for regional-residual separation of gravity anomaly

Adequate separation of regional-residual components from observed gravity anomaly is always a challenging task in gravity interpretation. Several techniques have been developed for effective regional-residual separation, however, no single approach can perfectly accomplish the job. In this work, a hybrid approach has been proposed with an objective to enhance the performance of Bi-dimensional Empirical Mode Decomposition (BEMD) in decomposing gravity anomaly by jointly employing low pass filter and BEMD. The paper discusses the efficacy of this hybrid approach in gravity anomaly separation from noisy synthetic and field data. Synthetic studies involving forward modelling of asymmetrically placed shallow and deeper spherical bodies with added Gaussian noises of different levels demonstrate that the proposed approach is more efficient in separating the regional-residual components from observed gravity anomaly compared to the individual application of filtering or BEMD. It has an added advantage of suppressing the unwanted noises significantly. After successful test with synthetic data the proposed approach has been applied to field data and satisfactory results are obtained. Thus, the proposed hybrid approach is more effective in delineating gravity signature related to complex near surface features even from noisy gravity data.

Three-dimensional gravity inversion using automatic regional-residual components separation with application to the Iwaki area in Fukushima Prefecture, Japan

We have developed a simple method for analysing gravity data to define 3D subsurface structures consistent with geological maps and reflection seismic survey results. This new method makes it possible to automatically separate gravity anomalies caused by structures that are the target of analysis (residual gravity) and not subject to gravity anomaly analysis (trend surfaces or regional gravity variations). This separation is achieved by assuming that the gravity anomaly trend surface is extremely smooth prior to analysis. In addition, this analysis can be carried out automatically, so it is possible to use a boot-strap simulation to evaluate the effect that gravity data accuracy and survey point distribution have on the analysis results. Using this newly developed method, we conducted a 3D subsurface structural analysis based on newly obtained gravity survey data in an area around Iwaki City, Fukushima Prefecture. The results of the 3D structural analysis revealed sharp depressions in the basement rock and basin-shaped underground structures along the Yunodake and Yamada faults. Finally, we were able to estimate the influence of survey point distribution and abrupt changes in the structure on the analysis results using a boot-strap simulation of the 3D analysis.

Determination of Geothermal Energy Sources in Masu Area Northeastern Nigeria Using Spectral Analysis of Aeromagnetic Data

The incessant power outage and power rationing in Nigeria has affected the economic development, hence the need to seek for other sources of electricity generation such as geothermal energy which is environmentally friendly and renewable. The wide range of geologic formations in the north-eastern Nigeria provides an avenue for exploration of geothermal energy. Hence, this work carries out an investigation of Curie point depth, geothermal gradient as well as heat flow in Masu, which is located within Nigerian sector of Chad Basin (lat. 12°00' to 13°00' N and long. 12°30' to 14°00' E) using spectral analysis. Application of minimum curvature in gridding the total magnetic field intensity data was done using the Oasis Montaj 6.4.2 software. First order polynomial fitting was applied in Regional-residual separation. The Curie point depth obtained ranges from 12.233 to 16.184 km with an average of 13.993 km, the geothermal gradient of the area varies from 35.838 to 47.413°C /km, with an average of 41.821°C /km, while the heat flow ranges from 89 to 117.80 mWm^-2, with an average of 104.551 mWm^-2. The 2D contour maps reveal that the Curie point depth is lowest in the southeast and increases towards the northwest, while the geothermal gradient and heat flow on the other hand are highest in the southeast and decrease towards northwest. The high geothermal gradient and heat flow values in the area are indications that the area might be suitable for geothermal energy generation as an alternative power supply in the area and in the country at large.

Structural interpretation of aeromagnetic data for the Wadi El Natrun area, northwestern desert, Egypt

The Wadi El Natrun area in Egypt is located west of the Nile Delta on both sides of the Cairo–Alexandria desert road, between 30°00′ and 30°40′N latitude, and 29°40′ and 30°40′E longitude. The name refers to the NW-SE trending depression located in the area and containing lakes that produce natron salt. In spite of the area is promising for oil and gas exploration as well as agricultural projects, Geophysical studies carried out in the area is limited to the regional seismic surveys accomplished by oil companies. This study presents the interpretation of the airborne magnetic data to map the structure architecture and depth to the basement of the study area. This interpretation was facilitated by applying different data enhancement and processing techniques. These techniques included filters (regional-residual separation), derivatives and depth estimation using spectral analysis and Euler deconvolution. The results were refined using 2-D forward modeling along three profiles.Based on the depth estimation techniques, the estimated depth to the basement surface, ranges from 2.25 km to 5.43 km while results of the two-dimensional forward modeling show that the depth of the basement surface ranges from 2.2 km to 4.8 km. The dominant tectonic trends in the study area at deep levels are NW (Suez Trend), NNW, NE, and ENE (Syrian Arc System trend). The older ENE trend, which dominates the northwestern desert is overprinted in the study area by relatively recent NW and NE trends, whereas the tectonic trends at shallow levels are NW, ENE, NNE (Aqaba Trend), and NE. The predominant structure trend for both deep and shallow structures is the NW trend.The results of this study can be used to better understand deep-seated basement structures and to support decisions with regard to the development of agriculture, industrial areas, as well as oil and gas exploration in northern Egypt.