Subsurface Structural Elements Research Articles

Geophysical structural interpretation of Esh El Mallaha basin, southern Gulf of Suez: implications for oil potential in South Malak and Rabeh fields

Esh El Mellaha area is located at the western margin of the Gulf of Suez rift system. It is one of the most important potential hydrocarbon resources in the north Eastern Desert. Satellite images, field observations (e.g. measure relevant structures, lineaments mapping, compile maps at the outcrops) and seismic data were used to delineate the surface and subsurface structural elements of the area west of Esh El Mellaha range. The present study revealed that, the main structural trends have the directions NW–SE, NE–SW to NNW–SSE, WNW–ESE and ENE–WSW. The NW–SE trending faults are the major dominating trend which is related to the Gulf of Suez rift opening. The seismic interpretation step led to the identification of four prominent continuous reflectors and five depositional seismic sequences. The recognised seismic reflectors were named; Q, F, R and K and ranging in age from the Lower Miocene to the Middle–Upper Miocene. The petrophysical examination exhibits good reservoir quality for the sandstones of Matulla Formation in Rabeh and South Malak fields, southern Esh El Mellaha area. These reservoirs display low shale volume (5–20%); high effective porosity (10–20%), relatively low water saturation (40–55%) and pay thickness varies between 30 and 85 ft. Accordingly, this study highlights the oil potentiality of the Matulla sandstones for further exploration purposes in both Rabeh and South Malak fields.

Subsurface structural characterization as deduced from potential field data—West Beni Suef, Western Desert, Egypt

The goal of present study is determining subsurface structural elements by analyzing geomagnetic data sets aiming to examine their impacts on geological surface structures characterizing the western region in Beni-Suef Governorate, Western Desert, Egypt. A land-magnetic survey is conducted by two exceedingly sensitive proton magnetometers to measure the total intensity of geomagnetic field at the region under investigation. The measurements of regional gradients and time variation were applied to get the required reduction of daily variation. The regional expansions of subsurface structural units were obtained after applying the reduction to north magnetic pole (RTP) method to the corrected magnetic data acquired from land-magnetic survey along with Bouguer maps (1:100,000 scale and 1-mGal contouring interval). Regional-residual technique was applied depending on the power spectrum analysis. Moreover, the edge detection approach is conducted to depict the structures and subsurface hidden anomalies. Different handling processes were applied for acquired land magnetic datasets such as Euler deconvolution and trend analysis. The results of current study revealed that four significant structural forces across the N-S, NW–SE, NE-SW, and E-W directions affected the region. Estimating the basement depth was accomplished using a number of spectral analysis techniques. The values of estimated depths are used for creating a basement relief map. Moreover, the achieved results show that depths to the basement at the region under study vary between 2.3 and 4.7 km.

Delineation of subsurface structures using gravity interpretation around Nabaa Al Hammara area, Wadi El Natrun, Egypt

ABSTRACT Nabaa El Hammra lies in the northeastern part of Wadi El-Natrun, characterised by low lands and most parts of this area are cultivated with different crops. In the current study, gravity data are used to investigate the subsurface structural features that can directly affect the configuration and distribution of groundwater aquifers and oil reservoirs accumulations. The present study aims to delineate the subsurface structural elements and to define the basins and basement uplifts, which can directly affect the flow of groundwater or oil accumulations. Gravity data are processed and filtered in diverse approaches to outlining the prevailed structure. The results of gravity data interpretation reveal that the studied area is affected by many structural features as NE-SW, NW-SE, N-S and E-W trends. These structural features caused barriers to the groundwater movement from or to the study area. The study revealed that the depth of the crystalline (Pre-Cambrian) rocks ranges from 3800 metres in the south part to 5300 metres in the northeastern region. Meanwhile, the basement rocks represent a bridge of shallow depth of northwest-southeast trend at the centre of the investigated area.

Identifying fault system and basement depth using aeromagnetic data beneath the Jahamah Platform, NE Sirt Basin, Libya

The Jahamah Platform is a part of a structural depression called the Sirt basin, located in the northern central part of Libya. The Jahamah Platform spans latitude 〖29.95〗^° N to 〖30.55〗^° N and longitudes 〖19.32〗^° E to 〖19.77〗^° E with an estimated area of about 2,187 km2. Libyan Petroleum Institute provided the data of aeromagnetic that was used in this study. The data was used to study the structure beneath the Jahamah Platform by using Oasis montaj software. Various filters from the software have been applied to enhance determining the fault system within the study area. An RTP filter was applied to the magnetic data to construct a reduction to the pole anomaly map. The subsurface structural elements underneath the study area were identified using Total horizontal derivative (THD), CET analysis, and Euler deconvolution. 2-D forward modelling of the area was constructed based on gravity data, and then the basement depth was estimated to range from 2.2 km to 3.1 km based on the model. Based on the interpretation of the constructed maps, the area has a number of faults that trend in NE-SW, NNW-SSE, N-S and NW-SE and faults depth ranging between 790 m to 3102 m.

Subsurface geological model of sedimentary and metasedimentary wedge from Mansehra to Battal based on gravity data, Hazara area, Pakistan

This study is aimed to delineate the subsurface structural elements using geophysical techniques in the Haraza area of Pakistan. We investigated the Oghi and Battal thrust faults, sedimentary and metasedimentary wedge, and the absolute crustal thickness based on terrestrial gravity data. Unlike seismic survey relying on wave propagation, magnetic survey is based on both attraction and repulsion, and electrical and electromagnetics on induction. The attractive gravity field produces relatively simpler patterns of anomalies, like a series of highs and lows over regions with undulating basements and buried structures. A qualitative interpretation of gravity data reveals a good deal of information. During the collision of Indian and Eurasian Plates, compressional structures were developed in the Lesser Himalayas or northwest of the Hazara Kashmir Syntaxis. The study mainly focuses on the western limb of the Hazara Kashmir Syntaxis. The regional and local Bouguer anomalies were incorporated to delineate the regional structural units. The gravity model is computed through geophysical technique along with profile A-A' from Mansehra to the Battal area that demarcates the blind Oghi Thrust and emergent Battal Thrust. Tanol Formation of Precambrian age demarcates the Oghi Thrust near Kotli Pine while the Battal Thrust is demarcated within the Mansehra Granite of Cambrian to Ordovician age near Battal. Along with the Battal Thrust, fault gouge and breccias have been observed during the field studies. The total thickness of the sedimentary/metasedimentary wedge in the Mansehra and Battal areas was estimated to be 13.6 km and 14.2 km. In comparison, the total thickness of crust in the Mansehra and Battal areas was 51.6 km and 52.2 km, respectively.

Research on sub-surface recrystallization of single crystal nickel-based superalloy in micro-milling

The micro-structure/parts of single crystal nickel-based superalloy materials are extensively used in high temperature environments. The recrystallization mechanism of the machined workpiece sub-surface is explained through energy storage model. A micro-milling experiment of single crystal nickel-based superalloy DD98 was performed by simulating the working environment at high temperature and setting different heat treatment temperature. By scanning electron microscopy (SEM), the influence of sub-surface structural elements on the properties of micro-milling workpiece was analyzed. Experimental results indicate that the recrystallization layer thickness of single crystal nickel-based superalloy DD98 increases with the increase of heat treatment temperature. When this temperature is between 950 °C and 1150 °C, the recrystallization thickness is 5–20 μm. The recrystallization of sub-surface layer takes the form of equiaxed recrystallization. Those provide basic data for restraining recrystallization of single crystal materials and have good scientific significance.

Radar probing of Jovian icy moons: Understanding subsurface water and structure detectability in the JUICE and Europa missions

Radar probing of Jovian icy satellites is fundamental for understanding the moons' origin and their thermal evolution as potential habitable environments in our Solar System. Using the current state of knowledge of the geological and geophysical properties of Ganymede, Europa and Callisto, we perform a comprehensive radar detectability study to quantify the exploration depth and the lower limit for subsurface identification of water and key tectonic structural elements. To achieve these objectives, we establish parametric dielectric models that reflect different hypotheses on the formation and thermal evolution of each moon. The models are then used for FDTD radar propagation simulations at the 9-MHz sounding frequency proposed for both ESA JUICE and NASA Europa missions. We investigate the detectability above the galactic noise level of four predominant subsurface features: brittle-ductile interfaces, shallow faults, brine aquifers, and the hypothesized global oceans. For Ganymede, our results suggest that the brittle-ductile interface could be within radar detectability range in the bright terrains, but is more challenging for the dark terrains. Moreover, understanding the slope variation of the brittle-ductile interface is possible after clutter reduction and focusing. For Europa, the detection of shallow subsurface structural elements few kilometers deep (such as fractures, faults and brine lenses) is achievable and not compromised by surface clutter. The objective of detecting the potential deep global ocean on Europa is also doable under both the convective and conductive hypotheses. Finally, for Callisto, radar waves can achieve an average penetration depth of ∼15km, although the current understanding of Callisto's subsurface dielectric properties does not suggest sufficiently strong contrasts to produce unambiguous radar returns.

Evidence of episodic long-lived eruptions in the Yuma, Ginsburg, Jesús Baraza and Tasyo mud volcanoes, Gulf of Cádiz

High-resolution single channel and multichannel seismic reflection profiles and multibeam bathymetric and backscatter data collected during several cruises over the period 1999 to 2007 have enabled characterising not only the seabed morphology but also the subsurface structural elements of the Yuma, Ginsburg, Jesus Baraza and Tasyo mud volcanoes (MVs) in the Gulf of Cadiz at 1,050–1,250 m water depth. These MVs vary strongly in morphology and size. The data reveal elongated cone-shaped edifices, rimmed depressions, and scarps interpreted as flank failures developed by collapse, faulting, compaction and gravitational processes. MV architecture is characterised by both extrusive and intrusive complexes, comprising stacked edifices (including seabed cones and up to four buried bicones) underlain by chaotic vertical zones and downward-tapering cones suggesting feeder systems. These intrusive structures represent the upper layer of the feeder system linking the fluid mud sources with the constructional edifices. The overall architecture is interpreted to be the result of successive events of mud extrusion and outbuilding alternating with periods of dormancy. Each mud extrusion phase is connected with the development of an edifice, represented by a seabed cone or a buried bicone. In all four MVs, the stacked edifices and the intrusive complexes penetrate Late Miocene–Quaternary units and are rooted in the Gulf of Cadiz wedge emplaced during the late Tortonian. Major phases of mud extrusion and outbuilding took place since the Late Pliocene, even though in the Yuma and Jesus Baraza MVs mud volcanism started in the Late Miocene shortly after the emplacement of the Gulf of Cadiz wedge. This study shows that fluid venting in the eastern sector of the Gulf of Cadiz promoted the outbuilding of large long-lived mud volcanoes active since the Late Miocene, and which have been reactivated repeatedly until recent times.

Assessment of subsurface structural elements around greater Cairo by using integrated geophysical tools

Geophysical techniques such as gravity, magnetic and seismology are perfect tools for detecting subsurface structures of local, regional as well as of global scales. The study of the earthquake records can be used for differentiating the active and non-active fault elements. In the current study, more than 2,200 land magnetic stations have been measured using two proton magnetometers. The data are corrected for diurnal variations and then reduced by the International Geomagnetic Reference Field. The corrected data have been interpreted by different techniques after filtering the data to separate shallow sources (basaltic sheet) from the deep sources (basement complex). Both Euler deconvolution and 3-D magnetic modeling were carried out. The results of interpretation indicate that the depth to the upper surface of basaltic sheet ranges from <10 to 600 m, depth to the lower surface ranges from 60 to 750 m, while the thickness of the basaltic sheet varies from <10 to 450 m. Moreover, gravity measurements are conducted at 2,250 stations using a CG-3 gravimeter. The measured values are corrected to construct a Bouger anomaly map. The least squares technique is then applied for regional–residual separation. The third order of least squares is found to be the most suitable to separate the residual anomalies from the regional one. The resultant third-order residual gravity map is used to delineate the structural fault systems of different characteristic trends. The trends show an NW–SE trend parallel to that of Gulf of Suez, an NE–SW trend parallel to the Gulf of Aqaba and an E–W trend parallel to that of the Mediterranean Sea. Taking seismological records into consideration, it is found that most of the 24 earthquake events recorded in the study area are located on fault elements. This gives an indication that the delineated fault elements are active.

Interpretation of aeromagnetic and gravity data in East Qattara Depression, North Western Desert, Egypt

The study area lies to the east of Qattara Depression at the north of the Western Desert, Egypt. It is bounded by latitudes 29°00′ and 30°00′ N and longitudes 28°00′ and 29°30′ E, including Abu Gharadig basin, which is the most petroliferous basin in the Egyptian Western Desert. Numerous exploratory wells show that the area is characterized by a thick sedimentary section, unconformably overlying the basement rocks. The main objective of the present study is to outline the structural parameters controlling the area under consideration. Aeromagnetic and gravity data were subjected to the analytic signal, 3D Euler deconvolution and edge enhancement techniques. The Analytic signal and 3D Euler deconvolution were utilized mainly to locate the main subsurface contact zones and to determine the depth and structural indices of the expected causative subsurface structural elements. However, the edge enhancement technique was used with various windows to enhance the edges of subsurface structures. The structural indices were estimated to be ranging between 0.16 and 0.26, indicating that the area is mainly controlled by faults. The depth of these structural elements was also estimated to be ranging between <1.37 and 5.29 km. It has been shown that the structural elements of the study area have different directions, trending E-W, ENE, NW, and N-S.

Magnetic interpretation of north Gebel El Shallul area, central Eastern Desert, Egypt

The present work utilizes the aeromagnetic data supported by geology and remote sensing satellite data, to delineate surface and subsurface structural elements in north Gebel El Shallul area. Geologically, the area is covered by Precambrian basement rocks to the East (metasediments, metavolcanics, Hammamat sediments and younger granites) and Phanerozoic sediments to the West (Nubian Sandstones and Qouseir clastics). The Landsat image of the area gave additional detailed litholgic information which is very useful in identifying and discriminating the different lithologic rocks exposed in the area. Analysis of the structural lineaments of the Landsat image and the compiled geological map show that most of the well-developed structural lineaments have NW, NNW and ENE trends. The aeromagnetic data were analyzed and processed by several advanced techniques; reduction to the pole, regional-residual separation, second vertical derivative (SVD), analytical signal, Euler deconvolution and shadowgrams. The application of local power spectrum on the reduced to North Pole (RTP) aeromagnetic data indicated that the average depths to the near–surface and deep-seated causative magnetic bodies were found to attain 0.5 and 1.8 km, respectively. Therefore, the filtering of the aeromagnetic data at the two assigned interfaces was conducted to assist the discrimination of the residual (near-surface) and regional (deep–seated) magnetic anomalies. The prepared aeromagnetic maps have been interpreted qualitatively and quantitatively to deduce the structural elements which were used to construct a basement tectonic map for the area. The used analysis techniques helped to reveal many structural elements such as faults of different orders, uplifted blocks (antiforms or horsts) and subsided blocks (basins or synforms). It has been found that the NNW pronounced linear magnetic anomalies, normally and reversely magnetized, are associated with deep-seated diabasic dykes. The interpretation of the basement tectonic map of the area indicated the presence of a set of unexposed subsurface basic dykes running generally in NNW–SSE direction controlling the courses of major wadis in the study area. This set of NNW–SSE basic dykes are dissected by a NE–SW fault system. These two sets of fault systems were found to be matched well with that obtained from the Landsat image and geological map. It was found that the pronounced NNW direction is a predominant structural trend controlling the structural framework of the area.

Geoelectrical Survey for Groundwater Exploration at the Asyuit Governorate, Nile Valley, Egypt

Asyuit area is considered as the most promising area for irrigated agriculture and development in both the Eastern Desert and the Western Desert. Groundwater is the most important resources necessary for such development. Forty-two vertical electrical soundings (VES.'s), using Schlumberger array were carried out in Asyuit area. The main goal of such survey was to elucidate hydrogeological information and to delineate subsurface structural elements. VES. curves were interpreted using a 2-D horizontal layering resistivity model assumption. The interpretation results showed that the geoelectrical succession consists of four layers. The top layer is formed of gravely sand with relatively high electrical resistivity values, the second layer is composed of sand (aquifer) with relatively intermediate electrical resistivity values, the third layer is made up of clay (aquiclude) with relatively low electrical resistivity values and the fourth layer consists of limestone with relatively high electrical resistivity values. As for groundwater potentiality, the second layer is highly promising to be the water-bearing layer. The maximum depth to water ranges between 9.9 to 522 m.

Neotectonics and Quaternary landscape evolution of the Gödöllő Hills, Central Pannonian Basin, Hungary

Quaternary landscape evolution of the Gödöllő Hills was governed by both structural and climate-related erosional processes. Considerable neotectonic deformation has been documented in the form of inversion of deep-seated earlier normal faults and transpressive reactivation of a syn- to post-rift transtensional strike-slip zone, the Tápió–Tóalmás Zone (TaTZ) and related en echelon folds. The structural inversion is mainly expressed by the folding of the uppermost pre-Quaternary horizons and deformation of the surface, which suggests late Pliocene-Quaternary (∼4–0 Ma) compressional–transpressional deformation with NE–SW maximal horizontal stress axis. Drainage anomalies can be frequently connected to neotectonic structures. The uplift of the anticline hinges led to enhanced surface erosion, river piracy and development of radial drainage networks. Minor amplitude of surface undulations respective to the amplitude of folds in the upper Miocene layers reflects the syn-folding denudation of the surface during the early part of the neotectonic phase (late Pliocene to early Quaternary). On the other hand, the NW–SE-trending rectilinear features of the landscape show no tectonic control, they were shaped mostly by deflation. The combination of preliminary DEM analysis, field studies and the mapping of subsurface structural elements proved to be successful in separating landforms developed under or in absence of neotectonic control. The presence of landforms controlled by neotectonic structures suggests ongoing deformation of the Central Pannonian Basin.

Contrast enhancement of pollen perforations for image analysis

Variation in pollen grain sculpturing constitutes one source of taxonomic evidence. With closely related species, this variation is primarily quantitative. Computerized image analysis produces accurate measurements of pollen surface features, thus making objective comparisons of quantitative sculpture variations possible. This study concerns manual methods that provide necessary contrast to features on reticulate or perforate pollen grain surfaces for image analysis. Repeatability of these methods was tested by statistically analyzing results of seven individuals. Image analysis was conducted using Kevex Feature Analysis software (Version 2.10) on a Delta class computer (Kevex Instruments, Inc., San Carlos, CA).In image analysis, features are designated by “painting” specific regions of the gray scale. A prerequisite for “painting” is sufficient contrast between features and non-features. With pollen, this requirement is often not met because: (1) surface perforations or openings (called lumina if sculpture is reticulate) sometimes contain subsurface structural elements (Fig. 1); or (2) lumina cannot be differentiated based on contrast (Fig. 2).

Seismic Structure and Stratigraphy of Eastern New York-Western Vermont: ABSTRACT

A reconnaissance grid of 550 mi of Vibroseis data extending from northernmost Vermont to slightly north of Albany, New York, provides a framework for analyzing subsurface structure and stratigraphy of eastern New York and western Vermont. Regional stratigraphic analysis based on outcrop sections indicates northward and eastward thickening of the Cambrian-Ordovician shelf sequence. Synthetic seismograms from wells in Quebec and southwestern Washington County, New York, document this change in the subsurface and correlate the seismic stratigraphy. Seismic data indicate thickening occurs north of the Whitehall culmination, an approximately 40-mi long buttress area of Adirondack Grenville basement. Changes in thickness appear to be gradual and not fault controlled. Foreland thrust systems of New York and Vermont relate via a displacement transfer or lateral ramp zone associated with the Whitehall culmination. Both thrust systems accomplish final emplacement of metamorphic sheets, deform them, and transport shelf material, which is predominantly shale in New York with increased percentage of carbonates in Vermont. Deflection of several major structural elements illustrates the culmination's buttress effect. Subsurface structural elements in New York include western graben, central horst block, and eastern fault-zone trends. No analogous trends have been identified in Vermont where predominant faulting is down-to-the-east. Significantly, in southwestern Washington County, New York, preexisting horst blocks do not serve as ramps to deflect thrusts upward. Instead, the Snake Hill-Smiths basin and Schuylerville thrusts shear off the upper sedimentary sequence of the horst and transport it westward. End_of_Article - Last_Page 298------------