Anticlinal Structure Research Articles

Geochemistry of organic matter and elements of black shale during weathering in Northern Guizhou, Southwestern China: Their mobilization and inter-connection

Different from previous studies on effect of weathering upon geochemical variation along a single weathered profile, this paper provides a new methodology validated by comparing a weathered outcrop samples and their stratigraphic counterpart un-weathered core samples in a nearby shallow borehole. This outcrop and borehole penetrated the Ordovician-Silurian Wufeng–Longmaxi shales, located in the same anticline structure in the northern part of Guizhou Province, Southern China. The mineral composition, major, trace and rare earth elements (REEs) composition and Rock-Eval parameters of outcrop and core samples were analyzed and compared. Organic matter (OM) was observed in the microscope and extracted for elements analysis. The results show that short-term weathering still has significant influence on OM, mineral and elemental composition of black shales. The elements composition shows the outcrop profile was moderately weathered. The REEs compositions do not alter much during weathering process and the REEs composition and their relative ratios still are valid for rock origin determination. The OM, mainly composed by graptolite and bitumen, even entering the highly-over thermal maturity, is still sensitive to the weathering with a systematic loss 30–50% of TOC along the outcrop profile, which suggests that the OM consumption is predominantly controlled by weathering duration and the distance from the weathering surface. In turn, OM has significant influence on the trace elements transportation behavior during weathering. Some trace elements associated with the OM such as V, Cr, Th, U, Ni and Co, change significantly in their absolute concentration during weathering, but their relative ratios do not necessarily change too much and might be still reliable proxies for paleo-environmental determination. The mobility of shale minerals during weathering is in the following order: plagioclase > potassium feldspar and dolomite >pyrite and OM. Short-term weathering can also result in considerable transportation of elements and significant variation of minerals content in black shale, which may pose potentially high environmental and engineering risk in the regions rich in black shale.

Pressure response of large-scale compressed air energy storage in porous formations

Large-scale compressed air energy storage (CAES) in porous formations can contribute to compensate the strong daily fluctuations in renewable energy production. This work presents a hypothetical CAES scenario using a representative geological anticlinal structure in Northern Germany and performs numerical simulations to estimate pressure response in the storage formation. The results show that the induced pressure changes laterally throughout the storage formation are due to initial fill of the air storage. Because of high air compressibility, the pressure fluctuations caused by daily cyclic operation can only be observed in the gas phase which reaches a distance of roughly 500 m.

Improving the Relationship Between Flow-Zone Indicators With Lithofacies

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 186005, “An Innovative Approach Toward Improving the Relationship Between Flow-Zone Indicators With Lithofacies: A Case Study in a Carbonate Oil Field in the Middle East,” by N.S. Hashim, A.F. Zakaria, and N.A. Ishak, Petronas, prepared for the 2017 SPE Reservoir Characterization and Simulation Conference and Exhibition, Abu Dhabi, 8–10 May. The paper has not been peer reviewed. The F field in the Middle East currently has more than 40 producing wells in the center of the structure. The uneven well distribution limits the understanding of 3D reservoir characterization, particularly in the flank areas. A fit-for-purpose integrated reservoir-characterization study was carried out. The exercise, outlined in the complete paper, confirms the heterogeneity within B formation (the primary oil reservoir within F field), and it captures the changes in reservoir quality laterally and vertically. Introduction F field is located in the northeastern part of the Arabian Peninsula. F field is a low-relief anticlinal structure aligned northwest/southeast, approximately 31 km long and 10 km wide. B formation consists of carbonate-ramp depositional settings, and has an average thickness of 200 m. Multiple development wells were drilled as part of its development plan, and its first oil production was achieved 3 years ago. Issues with reservoir characterization have arisen because of the uneven well distribution, especially in the flank area. Furthermore, only one conventional core with good recovery was available for Reservoir B, which makes it somewhat difficult to delineate the internal architecture of the carbonate ramp. B Formation Stratigraphic Interval B formation subreservoirs include Upper B (UB), Middle B (MB), and Lower B (LB); the MB and LB subreservoirs contain most of the hydrocarbon deposits. UB does not contain any hydrocarbons and is believed to be tight on the basis of log information. Each subreservoir was divided into sub-units (UB-1 and UB-2; MB-1, MB-2, and MB-3; and LB-1, LB-2, and LB-3) on the basis of pressure and fluid information. One conventional core was taken with a total length of 100 m and total core recovery of 97%. This conventional core covers the Middle B to Lower B subunits. Full-core analysis study was conducted on this conventional core, which includes routine geological analysis, routine core analysis (RCA), special core analysis, and digital rock analysis. Lithofacies Analysis The study identified seven lithofacies. Bioclastic Mudstone (BM). BM consists of a mostly micrite matrix. It is light gray to pale brown and is moderately bioturbated. In terms of reservoir characteristics, this lithofacies is poor, with no visible porosity. BM is usually deposited in an open marine slope. Bioclastic Wackestone (BW). As with BM, BW also consists of a micrite matrix. Carbonaceous wispy seams, solution seams, and stylolization are also common in this lithofacies. BW is characterized as tight, with no visible porosity. Its measured porosity ranges from 4 to 21%, with average porosity of only 10% and a permeability range between 0.1 and 7.6 md. BW is likely located in the shallow marine middle ramp.

Petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas, northern deep-water Gulf of Mexico: Traps, reservoirs, and tectono-stratigraphic evolution

The petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas, offshore northern Gulf of Mexico, is controlled by the interaction of salt tectonics and high sedimentation rate during the Neogene and resulted in a complex distribution of reservoirs and traps. We evaluate 87 fields and discoveries: 51 with combined structural/stratigraphic traps (three-way closures), 19 with structural traps (four-way closures), and 17 with stratigraphic traps. Three of these discoveries are in Upper Jurassic eolian reservoirs; the remaining discoveries are in Neogene deep-water reservoirs. The tectono-stratigraphic evolution of the area is analyzed at 11 discrete intervals between 24 Ma and the present. Four stratigraphic external forms—troughs, bowls, wedges, and sheets—are integrated with the structural geology to understand the changing shape of subbasins and minibasins, primarily in a slope setting. This analysis shows how the allochthonous salt systems evolved over time and how salt movement affected sedimentation patterns and subbasin evolution. The study area includes some of the largest fields in the northern deep-water Gulf of Mexico, such as the Thunder Horse field, which produces from an anticlinal (turtle) structure, or the Mars–Ursa and associated fields with greater than 1.5 billion BOE estimated ultimate recovery, which developed with a counterregional allochthonous salt system. The remaining fields have considerably smaller reserves, which are controlled by the area within closure and the number of reservoir intervals. Most of fields in the study area are contained within sheet-shaped or wedge-shaped stratigraphic external forms and have four-way or three-way trapping configurations. These findings indicate the profound effect of mobile salt on the petroleum geology of the region.

Seismic and well logging interpretation for evaluation of the lower Bahariya reservoir, southwest Qarun (SWQ) Field, Gindi Basin, Egypt

This paper focuses on seismic and well log interpretations for evaluating the sandstones of the Cenomanian Bahariya Formation in the southwest Qarun Field, Gindi Basin, northern Western Desert of Egypt. The seismic profiles display a clear anticlinal structure intersected by reverse faults in the study area. This faulted anticline has been interpreted to be one of the Syrian arc system folds formed by Upper Cretaceous tectonic inversion, which resulted from the NW movement of the African Plate relative to Laurasia. This anticline has been recommended as a target for exploration by the present work as it may represent a structural trap for hydrocarbon accumulation. The sandstones of the Lower Bahariya Formation in the southwest Qarun Field display good reservoir characteristics. The interpretation of the available well log data for the SWQ-21 and SWQ-25 wells for the Lower Bahariya Formation reflects a good reservoir quality for oil production in its topmost part. This reservoir possesses low SW (<50%), high porosity (16%), low SW/SXO and low BVW (<0.09) which all reflect a high potential for oil production.

Evidence for Deeper Hydrocarbon Exploration: New Insight from the Hydrocarbon Plays in the North Celtic Sea Basin

This study adds to previously published works, which were based on 1D modelling, by generating 2D models using PetroModTM software. Seismic data have been used to reconstruct the regional structural framework, while the integrated wireline logs and geochemical data provided lithological, porosity, and palaeothermal information. The palaeothermal values and available vitrinite reflectance data have been used to calibrate the models to present-day heat flow of 52mW/m2. Results from this study show that hydrocarbon maturation, generation, and migration were affected by the Triassic and Late Jurassic rifting activities, resulting in a complex charge history and trap modification through time. The Late Jurassic source rocks (PurbecK) attained peak maturation for oil in the late Cretaceous, while the Early Jurassic Source rocks (Liassic and Toarcian) entered the gas window in the Early Cretaceous. Analysis of the petroleum systems for deeper hydrocarbon prospecting suggests that two expulsion phases of hydrocarbons occurred in the Late Jurassic and Early Cretaceous, respectively. This result suggests that there is potential for the charge of suitable reservoir facies at depth if the reservoir quality can be preserved. Hydrocarbon preservation risk is low in anticlinal structures, but there is a high risk of hydrocarbon remigration along modified fault planes in fault-dependent structures. The study demonstrates how basin geometry has changed through time due to multiple tectonic events, leading to modification of older traps.

Reinterpretation of adcoh and cocorp seismic reflection data with constraints from detailed forward modeling of potential field data — Implications for Laurentia-Peri-Gondwana suture

To better constrain the structure of the Laurentian – Peri-Gondwana suture zone, maps and a 2-dimensional regional cross-section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields. The Central Piedmont Suture (CPS), the boundary between the Laurentian Inner Piedmont and the Peri-Gondwanan Carolina terrane is a low-angle thrust fault (~30°) ramping up from an Alleghanian mid-crustal detachment at depths of about 12km. ADCOH and COCORP seismic data image anticlinal structures in the footwalls of the Hayesville thrust and the CPS, above the Alleghanian decollement. The footwall rocks have previously been interpreted as Paleozoic shelf strata on the basis of sub-horizontal seismic reflectors; however, the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of Grenvillian basement. The Appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the Carolina Terrane toward the Appalachian core. A change in lower crustal density is not required, so that Grenville basement rocks may extend farther to the southeast than previously thought. The 5 to 10km of Alleghanian uplift and exhumation predicted by P-T crystallization data compiled in this paper can be easily accommodated by thrusting on four major low-angle thrust systems: Great Smoky Mountain Thrust (GSMT), Hayesville, Brevard, and CPS. Unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation. Alleghanian collision along the southeastern Appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter-clockwise rotation of Gondwanan West Africa, creating head-on collision in the southern Appalachians and at least 370km of shortening.

Seismic interpretation and petrophysical evaluation of SH field, Niger Delta

Three out of the 14 hydrocarbon-bearing sands (A, B and I) in the ‘SH’ field onshore Niger Delta which contain bulk of the hydrocarbon reserves in the field were considered as development candidates. Seismic interpretation and petrophysical evaluation of logs of 13 wells were integrated with the aim of verifying and ascertaining the hydrocarbon reserves prior to field development which involves enormous financial commitment. Results show that the field is structurally controlled by sets of northwest–southeast-trending synthetic faults which dip southwest. Hydrocarbon traps at the three sand levels are rollover anticlinal closures that are generally sealed by a major listric fault that demarcated the field into northwest and southeast blocks. The southern fault block is hydrocarbon bearing; wells drilled in the field targeted these closures and encountered a number of stacked hydrocarbon-bearing sand levels. Reservoir-A developed a hanging-wall rollover anticlinal structure sealed by a major listric fault forming a trap with oil–water contact (OWC) of 1222 m TVDSS. Reservoir-B also shows similar structure as reservoir-A, but it is partitioned into two hydrocarbon compartments by a sealing fault; these two compartments have different OWCs. Reservoir-I exhibits similar structure to reservoir-A. The evaluation of the petrophysical characteristics revealed that the reservoirs are of good quality with average net to gross, porosities, water saturation and hydrocarbon saturation ranging from 0.774 to 0.980, 0.220–0.339, 0.133–0.367 and 0.633–0.867, respectively. Variation in the petrophysical parameters and the uncertainty in the reservoir structure of the three reservoirs were considered in calculating range of values of gross rock volume and in-place volume. The study shows oil-in-place volume in the range of 243.83–357.90 MMstb in reservoir-I, whereas reservoir-A contains 148.98–241.14 MMstb, reservoir-B1 31.31–50.36 MMstb and reservoir-B2 67.79–108.98 MMstb of oil. Conclusively, this study has further confirmed the high productivity and commercial viability of the wells within the field of study to be able to adequately compensate for the cost of development.

Anisotropic full-waveform inversion with tilt-angle recovery

By allowing spatial variations in the direction of the anisotropic fast axis, tilted transverse isotropy (TTI) helps to image complex or steeply dipping structures. Without a priori geologic constraints, however, recovery of all the anisotropic parameters can be nontrivial and nonunique. We adopt two methods for TTI inversion with tilt-angle recovery: one based on the familiar Voigt parameters, and another based on the so-called Chen and Tromp parameters known from regional and global seismology. These parameterizations arise naturally in seismic wave propagation and facilitate straightforward recovery of the tilt angle and anisotropic strength. In numerical experiments with vertical transversely isotropic starting models and TTI target models, we find that the Voigt as well as the Chen and Tromp parameters allow quick and robust recovery of steeply dipping anticlinal structures.

Compressed air energy storage in porous formations: a feasibility and deliverability study

Compressed air energy storage (CAES) in porous formations is considered as one option for large-scale energy storage to compensate for fluctuations from renewable energy production. To analyse the feasibility of such a CAES application and the deliverability of an underground porous formation, a hypothetical CAES scenario using an anticline structure is investigated. Two daily extraction cycles of 6 h each are assumed, complementing high solar energy production around noon. A gas turbine producing 321 MW of power with a minimum inlet pressure of 43 bar at 417 kg s −1 air is assumed. Simulation results show that using six wells the 20 m-thick storage formation with a permeability of 1000 mD can support the required 6 h continuous power output of 321 MW, even reaching 8 h maximally. For the first 30 min, maximum power output is higher, at 458 MW, continuously dropping afterwards. A sensitivity analysis shows that the number of wells required does not linearly decrease with increasing permeability of the storage formation due to well inference during air extraction. For each additional well, the continuous power output increases by 4.8 h and the maximum power output within the first 30 min by 76 MW.

Geology, structure, geochemistry and ASTER-based mapping of Neoproterozoic Gebel El-Delihimmi granites, Central Eastern Desert of Egypt

The Gebel El-Delihimmi granite intrusion, located in the Central Eastern Desert of Egypt, cuts the core of a major anticlinal structure of calc-alkaline metavolcanics and ophiolitic mélange rocks. The intrusion is microscopically differentiated into granodiorite, monzogranite, syenogranite and alkali-feldspar granite. Decorrelation stretch and band-ratio techniques were applied to Advanced Spaceborne Thermal Emission and Reflection Radiometer data. Processing of ASTER-SWIR bands enabled discrimination of El-Delihimmi granite phases and generation of a detailed lithologic map of the study area. The structural and microfabric data suggest that the El-Delihimmi granite underwent at least two phases of deformations. The first was related to the Najd fault system during which the older granodiorite phase of the intrusion was affected by sinistral ductile shearing. During the second phase, monzogranite and syenogranite in the intrusion were affected by brittle E–W compressional deformation. Geochemical data reported here reveal that the granodiorite phase has K2O/Na2O ratio <1 and represents an evolved calc-alkaline granite. The monzogranite, syenogranite and alkali-feldspar granite phases have K2O/Na2O ratio >1. The granite phases are generally I-type, metaluminous to slightly peraluminous and are interpreted as formed above subducted slabs of oceanic lithosphere rather than in continental collision zones.

Seismo-Stratigraphic and Structural Interpretation of Seismic Data of Titas Gas Field, Bengal Basin, Bangladesh

ABSTRACT In the present study, seismic interpretation has been carried out over Titas structure of Bengal basin, Bangladesh to figure out its seismo-stratigraphic and structural behavior. Seven well marked reflecting horizons (R-01 to R-07) have been identified within the Neogene sedimentary sequences using 18 seismic sections and well log data. A new seismic stratigraphy of Neogene sequences has been proposed for the Titas structure ruling out the traditional lithostratigraphy. The studied structure has been divided into 3 megasequences (MS1, MS2 and MS3). Reflector R-01 and R-03 represent the tops of the megasequence 2 (MS2) and megasequence 1 (MS1) respectively. These well marked reflectors are correlated with the top of the traditional litho-groups called Tipam and Surma. Reflectors R-02 and R-04 represent acoustic impedance boundaries within MS2 and MS1 due to lithological gradation. However, R-02 and R-04 are not considered as sequence/ formation boundaries because geologically these are not well defined. Reflectors R-05, R-06 and R-07 represent top of the gas-bearing zones A, B and C that belongs to MS1. All these interfaces or reflectors are anti-form with a central long crestal zone. It forms a north-south trending semi-domal sub-surface anticlinal structure having a semi-dome shaped closure. The structure is asymmetric with steeper eastern flank and gentler western flank. The crestal region is essentially plain with discontinuous reflection. The semi-domal nature of the anticline is in contrast to the neighboring narrow anticlines. Structural pattern suggests its development in relation to the NE-SW trending stress field due to convergence of Indian plate with Burmese plate. Structures of the shallower and deeper reflectors are formed at different phases of structural development.

Hydrogen storage in a heterogeneous sandstone formation: dimensioning and induced hydraulic effects

Large-scale energy storage in the geological subsurface (e.g. by storing hydrogen gas) may help to mitigate effects of a fluctuating energy production arising from the extensive use of renewable energy sources. The applicability of hydrogen (H 2 ) storage in a porous sandstone formation is investigated by defining a usage scenario and a subsequent numerical simulation of a storage operation at an existing anticlinal structure in the North German Basin. A facies modelling approach is used to obtain 25 heterogeneous and realistic parameter sets. The storage operation consists of the initial filling with nitrogen used as cushion gas, the initial filling with H 2 , and six withdrawal periods with successive refilling and shut-in periods. It is found that, on average, the storage can sustain a continuous power output of 245 MW for 1 week when using five storage wells, while peak performance can be as high as 363 MW, indicating that the storage is mainly limited by the achievable extraction rates. The median of the maximum pressure perturbation caused by this storage is around 3 bars and can be observed at a distance of 5 km from the wells.

A study of earthquakes induced by water injection in the Changning salt mine area, SW China

The features of earthquakes induced by water injection in the Changning salt mine area of China were analyzed using the pore pressure diffusion method. The relationships between maximum magnitude, cumulative seismic moment, and cumulative water loss volume were investigated. Results show that increased seismic activities near the Changning salt mine in recent years are closely related to water injection during salt mining. High-pressure water injection over a long period of time caused water to diffuse into rock cracks, which increased pore pressure on faults and induced ruptures. Injection-induced earthquakes were located below the injection sites, mainly aligned NW–SE, with most occurring southeast of the mine area. Such a distribution indicates that seismic activities were affected by anticline structures in the Changning area. Based on pore pressure diffusion considerations, the diffusion coefficient was estimated to be ∼0.15m2/s, with a slightly lower value west of the injection site than to the east. A semi-logarithmic linear relationship was found between cumulative seismic moment and cumulative water loss volume, while maximum magnitude increased with increasing volume of cumulative water loss. This study may provide reference material for analysis of injection-induced earthquakes and evaluation of the danger of earthquakes induced by water injection.

The Greenland–Iceland–Faroe Ridge Complex

Abstract The Greenland–Iceland–Faroe Ridge Complex (GIFRC) has been forming since the opening of the NE Atlantic (&lt;55 Ma), standing out as a prominent feature on all geoscientific datasets. Our interpretations have revealed several new potential abandoned rift centres, mapped as syncline and anticline structures. The synclines are suggested to be manifestations of former rift axes that were abandoned by rift jumps. These appear to be more common inside the GIFRC region than in the adjacent ocean basins, and can be confirmed by observations of cumulative crustal accretion data through time. A major post-40 Ma unconformity is proposed across the East Iceland Shelf, forming a distinct 16–20 myr-long hiatus that is covered by a thick, younger sedimentary section. Several seamounts were identified on multibeam datasets at around 1200 m water depth in the Vesturdjúp Basin, just south of the Greenland–Iceland Ridge. These seamounts appear to be younger in formation time than the surrounding ocean floor, possibly indicating a still active intraplate volcanic zone. Young tectonic features, such as faults, graben and transverse ridges, characterize the area and present a good example of the complexity of the GIFRC in comparison to the adjacent abyssal plain.

Tapping Difficult Oil in a Giant Carbonate Field in Qatar

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18296, “Tapping the Difficult Oil and Enhancing Reservoir-Development Strategy To Maximize Recovery From a Mature Waterflood Giant Carbonate Field in the Middle East: Arab C Reservoir, Dukhan Field, State of Qatar,” by Mohamed Naguib Bin Ab Majid, Carlos Troconiz, Mohammed Nedham Al-Shafei, Gheorghe Luca, and Ariel Cachi, Qatar Petroleum, prepared for the 2015 International Petroleum Technology Conference, Doha, Qatar, 7–9 December. The paper has not been peer reviewed. Copyright 2015 International Petroleum Technology Conference. Reproduced by permission. After 70 years of production, more than 30% of the Arab C reservoir stock-tank original oil in place has been recovered through various mechanisms including natural depletion, waterflooding, gas lift implementation, and horizontal-well development. Extending production into future years requires a strategic approach focusing on innovative development to target the remaining oil saturation. Integration of a recently acquired, high-resolution 3D-seismic survey complements the data available for subsurface description and characterization, positively affecting reservoir-model history-matching metrics. Introduction The large, mature Dukhan field is located onshore Qatar, approximately 80 km west of Doha. The Arab C reservoir interval is a carbonate anticlinal structure lying 5,500 to 7,000 ft below the surface. Areally, the Arab C reservoir has been divided into four structural elements from north to south (i.e., Khatiyah, Fahahil, Jaleha, and Diyab). The first three sectors comprise the continuous oil-bearing extent of the reservoir, while Diyab is water-bearing on the basis of results from wells drilled to date (Fig. 1). Arab C is an undersaturated-oil reservoir. The original oil column ranged from 1,400-ft thickness in the Khatiyah sector to 400 ft in the Jaleha sector. It has a weak to moderate connected aquifer lying below the oil column. Arab C development started with vertical wells, initially completed openhole. Increase in water production led to a well-completion-scheme change; vertical wells were then completed cased-hole and perforated selectively. Horizontal drilling commenced in 1992 to improve recovery and enhance production. As the water front from injection progressed, gas lifting in Arab C was initiated in 2003 to continue producing the high-water-cut wells. Currently, 60% of the Arab C producers are flowing under gas lift assistance. Reservoir Description Arab C is a heterogeneous organization of limestone and dolomite lithologies deposited on a shallow-water Jurassic ramp system. Hydraulically, the 80-ft-thick interval represents a net-work of grainstone conductors compartmentalized by muddy carbonate baffles resulting in layer-constrained dynamic behavior. Lateral ranges of 1 to 4 km for baffling thin beds support a localized layer-constrained dynamic behavior and a high degree of vertical heterogeneity, though communication pathways are impacted by sporadic occurrences of cross-cutting conductive and resistive faults. Reservoir porosity is 15 to 20%, and the average permeability is approximately 150 md, but this varies widely on the basis of reservoir zone.

Construction of a Structural Model for Harir Anticline within Zagros Fold-Thrust belt, Kurdistan of Iraq

Abstract The study area is considered to be a part of Arabian plate, located within High Folded Zone of the Zagros Fold-Thrust Belt in the Iraqi Kurdistan Region. This area consists of a major anticline called Harir anticline. The study of this structure was conducted along five traversal sections through 57 field stations in order to understand the geometry and elucidate structural model for generation and propagation of this fold. Thirteen formations were exposed covering this anticline, ranging in age from Early Cretaceous up to the Pleistocene. Geometrical analysis of Harir fold indicates that this fold is asymmetrical double plunging anticline, gentle to open and non-cylindrical, curvi-planar anticlinal structure. Due to presence of three strike slip-faults cross cutting this anticline, it segmented into four transversal blocks which are namely Batas, Harir, Sheikh-Mamudian and Ashkafta blocks. Each block has its own structural, sedimentlogical, and morphological properties making it different from the other blocks. Detailed balanced and retro-deformable cross sections in the studied area reveal that the shortening increases gradually from northwest toward middle part and decreases towards southeastern part of Harir Anticline. The calculated shortening consecutively is 6.76%, 14.30% and 14.31 % 10.52%, 5.48% from northwestern plunging area to the southeastern plunge. The depth to detachment surface has been calculated, ranging between 10-10.5km below the regional level of Bekhme Formation. This depth coincides with surface of the Upper Paleozoic Ora shale formation, which indicates this anticline is generated from this depth and propagated upwards. Structural model is constructed for this anticline taking into consideration the two mechanisms informing this structure; one is the occurrence of slipping along detachment surface and second is the effect of the strike-slip faults (Tear faults) cross cutting Harir structure. These two mechanisms acted synchronously and beginning at least from Late Cretaceous to the end of the Tertiary.

Inversion tectonics in Central Africa Rift System: Evidence from the Heglig Field

The Mesozoic-Cenozoic tectonic history of the Muglad Basin, is dominated by extension and inversion tectonics, but evidence of the inversion tectonics has not been well documented yet. In some other rift basins of CARS and WARS the phase of the inversion tectonics is well documented by several authors.This paper presents a structural study of the Heglig field area located on the eastern flank of the Muglad Basin. Detailed 3D seismic interpretation allows a better understanding of the structural style of the Heglig field. The new structural analysis has shown that the Heglig field has a complex structural framework reflected in the presence of a combination of two structural styles. The extensional structure is influenced by inversion tectonics during the Santonian time that creates four-way dip anticline structure, overprinted by the subsequent extensional movement that creates tilted fault block. The presence of inversion tectonics has supported by different means including seismic reflection, velocity, and source rock maturity data. The authors attributed the trapping of oil in the Lower Bentiu reservoir, that requires a horizontal seal, to the presence of the four-way dip anticline structure created by the inversion tectonics.The current interpretation of the Heglig field 3D seismic data sheds new light on the development and evolution of a key structure in the Muglad Basin. The results help to resolve long-standing discussion concerning hydrocarbon accumulation of the lower part of Bentiu Formation that lacks horizontal sealing.

Mapping Sub-Surface Geology from Magnetic Data in the Hides area, Western Papuan Fold Belt, PNG

Horizon mapping using magnetic data was conducted over a part of the Western Papuan Fold Belt, in an area of rugged terrain, where the geological structures are of relatively low complexity. Energy spectral analysis was used to detect magnetic susceptibility contrasts that were laterally merged to form magnetic interfaces corresponding to horizons derived from seismic and well data.Numerous magnetic interfaces were detected corresponding to: magnetic layers within the Darai Limestone, top of Ieru Formation, intra-Ieru and deeper intra-sedimentary boundaries. These mapped sedimentary surfaces form an anticlinal structure which plunges towards the south-east. A major thrust fault, mapped from magnetic data using automatic curve matching, truncates the anticline in the south-west. Sedimentary magnetic layers were mapped on both sides of this fault. The results obtained from the interpretation of the magnetic data are consistent with structures mapped from seismic and well data.

Perspectives of using the geological subsurface for hydrogen storage in Poland

The increasing share of renewable energy in electricity production in Poland is part of the growing interest in the hydrogen underground storage. In the search for suitable locations for this purpose it is useful to have the knowledge on the geological structures for underground storage of gases, including carbon dioxide.This article presents the possibilities of geological storage of hydrogen in underground geological structures in Poland (salt caverns, depleted oil and natural gas fields, and deeply seated aquifers). The study results confirm that there are favorable conditions to achieve this goal – in many areas of Poland it is possible to realize some type of hydrogen underground storage.The paper presents prospective areas for different options of hydrogen underground storage at specified conditions. For locations in salt caverns, rock salt deposits from the following areas are proposed: Łeba Elevation, Fore-Sudetic Monocline, Carpathian Foredeep, and salt stocks in the Polish Lowlands. For depleted oil and natural gas fields in the Polish Lowlands, Carpathians and Carpathian Foredeep, a few tens of fields are indicated, most of them are natural gas deposits. In the Polish Lowlands, several anticlinal structures in the Lower Cretaceous and Lower Jurassic formations have been selected. These pre-designated locations may be the basis for further work and detailed considerations in order to find the best and most appropriate locations intended for hydrogen underground storage.