Discontinuous Reflections Research Articles

An artificial intelligence workflow for horizon volume generation from 3D seismic data

Horizon-based subsurface stratigraphic model building is a tedious process, especially in geologically complex areas where seismic data are contaminated with noise and thus are of weak and discontinuous reflectors. Seismic interpreters usually use stratal (proportional) slices to approximately inspect 3D seismic data along seismic reflectors yet to be interpreted. We introduce an artificial intelligence workflow consisting of three deep learning steps to provide a conditioned seismic image that is easier to interpret, a stratigraphic model that outlines major formations, and moreover a relative geologic time volume that allows us to automatically extract an infinite number of horizons along any seismic reflectors within a seismic cube. Depending on the availability of interpreters, the proposed workflow can either run fully unsupervised without human inputs or using sparse horizon interpretation as constraints to further improve the quality of extracted horizons, providing flexibility in both efficiency and quality. Starting from only seismic images and a few key horizons interpreted on very sparse seismic lines, we demonstrate the workflow to generate a stack of complete horizons covering the entire seismic volume from offshore Australia.

Crustal structure beneath the Jiamusi Block and the Nadanhada Terrane from seismic and magnetotelluric studies: Implications for the subduction of the Pacific Plate

The Nadanhada terrane is considered to accrete to the eastern end of the Jiamusi Block during the Pacific Plate subduction. Constraints on the deep structure of the Nadanhada terrane and Jiamusi Block are essential to study the evolution, transformation and current activity of the eastern Asian continental margin. To reconstruct the accretion processes, two magnetotelluric sounding sections and a seismic reflection section were conducted in the eastern part of Jiamusi Block, the middle, and the southern end of the Nadanhada terrane respectively. Geophysical data revealed resistant stable structures and west-dipping discontinuous reflections with a thickness of around 15 km in the upper crust of Jiamusi Block. In contrast, the lower crust of the Jiamusi block exhibited high conductivity and short sub-horizontal reflections that suggest upwelling of mantle material under Pacific Plate subduction. Moreover, the low resistivity zone observed connecting the shallow crust with the upper mantle in the Tongjiang-Yuejinshan fault was interpreted as the boundary line between the Jiamusi block and Nadanhada terrane. The Nadanhada terrane can be subdivided into the Yuejinshan and Raohe complexes based on their distinct geophysical features. The Yuejinshan Complex is characterized by irregular bodies with high resistivity and short arc reflections with a thickness of about 10 km. In contrast, the Raohe Complex displays high-resistivity blocks and west-dipping thrust nappe strong reflections with a thickness of about 5 km. Additionally, the high-conductivity layer located between the Raohe Complex and the underlying basement is believed to be the detachment zone. Since the Cretaceous, the continuous subduction of the Pacific Plate has caused magmatism that has led to the high conductivity crust. The observation of low-resistivity channels and arcuate reflections within the crust supports the notion of upwelling of mantle-derived materials brought about by the subduction of the Pacific Plate in the Cenozoic era.

Exploring for groundwater in sub-Saharan Africa: Insights from integrated geophysical characterization of a weathered basement aquifer system, central Malawi

Study RegionMkonga village, ∼35 km southwest of the capital city of Lilongwe on the central plains in Malawi, Africa, located at the crest of a local topographic-high characterized by crystalline basement. Study FocusGroundwater aquifer systems in the shallow buried crystalline basement are geologically complex reservoir targets with historically low drilling success rates. Understanding the basement weathering profiles and their implications for aquifer architecture is crucial for drilling productive wells. This is particularly critical in developing countries where water demands are rising. This study employs an integrated approach of 2-D seismic reflection and 2-D electrical resistivity imaging, constrained by borehole data to characterize the local basement aquifers in the crystalline-dominated terranes of central Malawi. New Hydrological Insights for the RegionThe integrated geophysical and borehole data reveal a layered weathering profile: shallow thin laterite and sub-lateritic layers, the saprolite, the saprock, and the fractured/fresh basement. We identify four potential water-bearing zones consisting of the base of the sub-laterite layer, the saprolite, the saprock and the fractured basement. The most productive boreholes are those that intersect low resistivity anomalies (< 20 ohm-m) that are collocated with strong but discontinuous reflectors. These targets are interpreted to represent water-bearing zones that connect the saprolite and saprock to recharge pathways at the base of the sub-laterite.

Structured light 3-D sensing for scenes with discontinuous reflectivity: error removal based on scene reconstruction and normalization.

Structured light-based 3-D sensing technique reconstructs the 3-D shape from the disparity given by pixel correspondence of two sensors. However, for scene surface containing discontinuous reflectivity (DR), the captured intensity deviates from its actual value caused by the non-ideal camera point spread function (PSF), thus generating 3-D measurement error. First, we construct the error model of fringe projection profilometry (FPP). From which, we conclude that the DR error of FPP is related to both the camera PSF and the scene reflectivity. The DR error of FPP is hard to be alleviated because of unknown scene reflectivity. Second, we introduce single-pixel imaging (SI) to reconstruct the scene reflectivity and normalize the scene with scene reflectivity "captured" by the projector. From the normalized scene reflectivity, pixel correspondence with error opposite to the original reflectivity is calculated for the DR error removal. Third, we propose an accurate 3-D reconstruction method under discontinuous reflectivity. In this method, pixel correspondence is first established by using FPP, and then refined by using SI with reflectivity normalization. Both the analysis and the measurement accuracy are verified under scenes with different reflectivity distributions in the experiments. As a result, the DR error is effectively alleviated while taking an acceptable measurement time.

How do fault systems and seafloor bathymetry influence the structure and distribution characteristics of gas chimneys?

AbstractGas chimneys are key pathways for geofluid vertical migration; therefore, deciphering their formation and evolution is crucial for hydrocarbon exploration and geohazard risk assessment. However, the influences of ambient conditions (e.g. bathymetry, tectonics, sediment supply flux) on gas chimney development have not been thoroughly investigated. Using high‐resolution 3D seismic data, we have identified 59 gas chimneys beneath the Shenhu Slope (a gas hydrate test production area on the northern South China Sea margin), 35 of which intersect faults. Above fault interfaces, internal seismic structures are dominated by chaotic discontinuous reflections. Internal structures below interfaces display more continuous reflections, which are also apparent in gas chimneys, not intersecting faults. A higher degree of chaotic or discontinuous seismic reflections may indicate more fragmented networks. This may occur due to increased fluid flow along faults and concomitant fluid overpressure. The present‐day undulating seafloor comprises the inter‐canyon (IT) region, intra‐canyon (IN) region and flat slope (FD) region downstream of canyons. Gas chimneys beneath IT and IN regions exhibit elongated elliptical shapes in the plane, with the long axis azimuth (sub‐) parallel to the main strike of canyons. Chimneys beneath the IT region have larger heights than those beneath the IN and FD regions. Thicker sediment in the IT region corresponds to a higher overburden pressure, which may induce stronger overpressure in the subsurface reservoir region. This overpressure may promote chimneys gathering in the IT region. Canyons' main directions are likely to limit hydraulic fracturing due to maximum gradient boundaries between overlying sediment stress fields. This study provides insights into gas chimney distribution, morphology and structure evolution in relation to bathymetry and fault conditions. It contributes to an improved understanding of how geofluids migrate in marginal ocean basins.

Geophysical evidence for a serpentine mud volcano in the relict slow-spreading center of the South China Sea

The seamounts formed in spreading centers are of basaltic with prominent gravity peaks and high density. But Longmen Seamount, 1.5 km high and ∼ 20 km wide, located in the relict slow-spreading center of the South China Sea, shows a weak gravity peak with a low-amplitude gravity variation (∼19 mGal). To reveal the geological origin of the unusual seamount, we conducted pre-stack depth-migrated image and 3D forward gravity modeling for Longmen Seamount based on the constraint from reflection and refraction seismic data. Our results show that bulk density and seismic velocity of Longmen Seamount is as low as ∼2.1 g/cm3, and 1.6–3.2 km/s, respectively, equivalent to that of poorly consolidated sediments. Furthermore, typical structural elements of the mud volcano system, such as a reflection blank zone, up-bent and downward bending reflections, are observed beneath LM Seamount. For the crust beneath LM Seamount is thin (1.6 km) and highly faulted revealed by numerous clear discontinuous reflections, it is easy for seawater to infiltrate through the thin crust and leads to a high degree of serpentinization of the upper mantle rocks. Combined with serpentine mud volcanoes featuring low bulk density and low seismic velocity, Longmen Seamount is most probably a serpentine mud volcano in a slow-spreading mid-ocean center. For the discovered serpentine mud volcanoes are all restricted to the convergent plate margins, this study will lead to a new understanding of the mechanism of serpentine mud volcanism.

Computing dip-angle gathers using Poynting vector for elastic reverse time migration in 2D transversely isotropic media

Angle-domain common-image gathers (ADCIGs) have wide applications in seismic imaging. For isotropic elastic reverse time migration (ERTM), we can produce dip-angle ADCIGs by using conventional Poynting vectors. Seismic anisotropy widely occurrs in Earth materials, such as in the shales and fractured reservoirs. ERTM based on the isotropic elastic wave equation is unable to accurately image anisotropic structures, leading to noise, discontinuous reflection events and mispositioning in migration results. Hence, conducting ERTM and generating dip-angle ADCIGs for anisotropic media require solving the anisotropic elastic wave equation. However, it is challenging to compute the gathers using the conventional Poynting vector for anisotropic elastic media. In this study, we derive the group and phase Poynting vectors, in which we use the optical flow method to stabilize the phase-related Poynting vectors. This approach admits efficient calculation of dip-angle ADCIG in anisotropic media. It also suppresses noise in anisotropic ERTM. The results of numerical experiments demonstrate the effectiveness of the proposed method.

Multiattribute analysis of channel architectural elements within the deepwater Taranaki Basin, 3D Romney data

The Taranaki Basin is located offshore west of North Island, New Zealand. Within the study area, deepwater channel systems are present as a result of plate boundary movement and clastic deposition during the Plio-Pleistocene. Multiattribute analysis revealed a few interesting features that we identified and interpreted. After refining the horizon of focus, we have concluded some interpretations as noise, whereas others were confirmed as geologic deposits. In one funny-looking thing (FLT 1), we interpreted high energy and high sweetness response along the northwestern portion of the main channel body as a sand-rich levee deposit and, in a second funny-looking thing (FLT 2), scalloping and elongate “finger-like” geometries as noise. The visualization and interpretation of these features through seismic attributes allow for optimized exploration, and therefore an opportunity for hydrocarbon extraction, within the Taranaki Basin. Geologic feature: Deep marine channel system: sandy channel fill to the northwest (FLT 1); interesting features in the center of the time slice (FLT 2) Seismic appearance: Chaotic, discontinuous reflectors with a high-energy response (FLT 1); chaotic high-variance features (FLT 2) Alternative interpretations: Overlapping sand-dominated channel (FLT 1); crevasse splays, fan lobes, distributary channels, ravines, and incisions (FLT 2) Age: Plio-Pleistocene Location: Taranaki Basin, western offshore North Island, New Zealand Seismic data: Provided by Anadarko Taranaki Company Analysis tool: A 3D reflection seismic, geometric, and physical seismic attributes

Automatic Extraction of Seismic Data Horizon Across Faults

Most of the traditional horizon interpretation methods are based on the dip of the seismic data. Since the dip does not correctly reflect the discontinuous reflection characteristics of the events, these methods usually cannot extract the horizons containing faults well. Meanwhile, the field seismic data observed in complex areas are generally with low signal-to-noise ratio (SNR), which makes the extraction of horizons difficult. To address these problems, an automatic horizon extraction approach under fault control is investigated in this article. First, the horizon dip is obtained by using plane wave destruction (PWD), and the dip information can be utilized to control the overall trend of the horizon curve. Based on the dip information, we can also calculate the weight coefficients to characterize the faults. The fault characterization results can better guide the horizon extraction. Then, the dynamic time warping (DTW) is used for phase matching to further obtain the similar slope and describe the details of the horizontal curve. Finally, the horizon extraction equation is developed with the dip and phase information as the guide and solved iteratively to obtain the final horizon curve. The effectiveness of the presented approach is tested by both synthetic and field data. The results demonstrate that the presented approach can accurately pick the horizon information across faults and is more stable in the condition of low SNR compared with previous methods.

Revealing the geological materials properties by a shallow seismic method for investigating slope site effects: a case study of Qiaozhuang town, Qingchuan County, China

This article presents a description of the lithology and weathered features of the subsurface under Qiaozhuang Town through a 2-D interpretation based on a shallow seismic reflection geophysical survey. To obtain the overburden, phyllite, and limestone geological parameters for the dynamic effect assessment of the slope site, twelve shallow seismic profiles were collected in the target area at slope sites where intensive ground damage was caused by the Wenchuan earthquake. To expose the geological features of rock masses with different lithologies, six shots field recordings for each profile were performed. The results showed reflection signals of a seismic wave that exhibited four to five weathered layers within a shallow depth range. The interpretation of velocity analysis of the geological imaging shows that the elastic velocities of the reflection layers increase with depth. The overburden, the first layer of slope surface, had velocities in the range of 724 m/s to 1024 m/s with the thickness changing in a large domain from 5 to 25 m, which was partially revealed in an exploration shaft and in a borehole. In deeper bedrock, the limestone was characterized by a mean velocity of 1470 m/s to 3760 m/s and the phyllite was characterized by a mean velocity of 1440 m/s to 3580 m/s. Moreover, the geological imaging of partial profiles showed that a weak and discontinuous reflection seismic wave may be interpreted as a fractured zone. The interpretation results reveal that the elastic velocity changing with lithology material is clear presence, leading to the impedance contrast varies from the slope inside to the surface. In particular, the presence of lower velocity layer, such as the overburden, which big material impedance contrast (> 1.0) likely formed strong slope site effects. Therefore, the geological material property of the study area was probably another factor causing the slope failure during the Wenchuan earthquake.

3D anatomy and flow dynamics of net-depositional cyclic steps on the world\u2019s largest submarine fan: a joint 3D seismic and numerical approach

Supercritical flows are ubiquitous in natural environments; however, there is rare 3D anatomy of their deposits. This study uses high-quality 3D seismic datasets from the world’s largest submarine fan, Bengal Fan, to interpret 3D architectures and flow processes of Pliocene undulating bedforms that were related to supercritical flows. Bengal undulating bedforms as documented in this study were developed in unconfined settings, and are seismically imaged as strike-elongated, crescentic bedforms in plan view and as rhythmically undulating, upstream migrating, erosive, discontinuous reflections in section view. Their lee sides are overall 3 to 4 times steeper (0.28° to 1.19° in slope) and 3 to 4 times shorter (117 to 419 m in length) than their stoss flanks and were ascribed to faster (high flow velocities of 2.70 to 3.98 m/s) supercritical flows (Froude numbers of 1.53 to 2.27). Their stoss sides, in contrast, are overall 3 to 4 times gentler (0.12° to 0.27° in slope) and 3 to 4 times longer (410 to 1139 m in length) than their lee flanks and were related to slower (low velocities of 2.35 to 3.05 m/s) subcritical flows (Froude numbers of 0.58 to 0.97). Bengal wave-like features were, thus, created by supercritical-to-subcritical flow transformations through internal hydraulic jumps (i.e., cyclic steps). They have crests that are positive relative to the surrounding region of the seafloor, suggesting the predominant deposition of draping sediments associated with net-depositional cyclic steps. Turbidity currents forming Bengal wave-like features were, thus, dominated by deposition, resulting in net-depositional cyclic steps. Sandy deposits associated with Bengal net-depositional cyclic steps are imaged themselves as closely spaced, strike-elongated high RMS-attribute patches, thereby showing closely spaced, long and linear, strike-elongated distribution patterns.

Pre-salt clastic systems in the Herodotus Basin, SE Mediterranean Sea

This study is focused on the architectural characteristics of the offshore extension of a late Messinian deep-sea fan system through the analysis of a large set of multichannel seismic-reflection profiles. A 2 km thick Messinian Salinity Crisis sequence occurs on top of a clastic system, indicating that even during the maximum sea-level drop, this part of the basin was still a marine setting. The top of the clastic system is characterized by a sharp surface on which several shear surfaces within the overlying Messinian salt terminate. This is attributed to the northward gliding of the Messinian mobile salt layer from the Nile cone to the deep Herodotus basin. Mapping the base of the clastic system, it is concluded that the bathymetry on which it evolved was complex, forming valley-like structures in the southern half of the study area. The sediment source of this clastic system is interpreted to have originated from the Nile River through gravity flows during the early stages of the Messinian Salinity Crisis that resulted in thick deposits at the deepest parts of the Herodotus basin. Medium to high amplitude discontinuous reflections with multiple sudden terminations representing local (channel-like) to broader-scale erosional surfaces characterize the late Messinian clastic system. Such a seismic character, in combination with its confined nature, indicates the development of a submarine channel complex set. On the other hand, towards the north, the convex top surface of the clastic system and discontinuous internal reflections, exhibit in multiple occasions, bidirectional downlap geometries that point to the basinward evolution of the channel complex set into a lobe complex set at the most unconfined parts of the basin. This clastic system is time equivalent to the fluvio-deltaic deposits of the Abu Madi Formation of the Nile Delta region.

Seismic response to paleo-sand dunes in the Nugget Sandstone Formation, southwestern Wyoming

We have analyzed a 3D seismic survey acquired for a carbon sequestration project on top of the Moxa Arch in southwestern Wyoming. We observed a zone of discontinuous reflectors on vertical slices of seismic amplitude volume, whereas, the northwest–southeast lineations were observed on the time slices. We performed a seismic to well tie that suggested that the lineations occur within the Nugget Sandstone. The Nugget Sandstone is an eolian sandstone deposit of Early Jurassic age, deposited as a subtropical dune field, and equivalent to the Navajo Sandstone of southwestern Utah. Petrophysical analysis indicates that the Nugget Sandstone is dominated by clean sandstone (70%–80%), whereas evaporites, including halite and anhydrite, are present in certain zones. Previous outcrop studies on the Navajo Sandstone indicate the wind direction to be predominantly northeast–southwest. Seismic attributes, including coherence and curvature, displayed on stratal slices within the Nugget Sandstone interval indicate the presence of lineations in the northwest–southeast direction with irregular spacing. These lineations are approximately perpendicular to the inferred dominant wind direction. We computed the dominant wind direction from the average azimuth of the lineations as seen on the curvature attribute in the Nugget Sandstone interval. Geological feature: Eolian sand dunes with interdunal evaporites Seismic appearance: Parallel lineations with irregular spacing on seismic attribute horizon slices Alternative interpretations: Canyons at continental slopes; slope failures Features with a similar appearance: Marine bars; contourites Formation: The Nugget Sandstone — equivalent to the Navajo Sandstone Age: Early Jurassic Location: Moxa Arch, Wyoming Seismic data: Obtained by the University of Wyoming with U.S. DOE funding Contributors: Dhruv Agrawal, Brady Lujan, Sumit Verma, Shuvajit Bhattacharya, and Subhashis Mallick Analysis tools: Coherence and curvature attributes; seismic inversion; petrophysical inversion

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: a case study for the COSC-1 borehole, Sweden

Abstract. Deeply rooted thrust zones are key features of tectonic processes and the evolution of mountain belts. Exhumed and deeply eroded orogens like the Scandinavian Caledonides allow us to study such systems from the surface. Previous seismic investigations of the Seve Nappe Complex have shown indications of a strong but discontinuous reflectivity of this thrust zone, which is only poorly understood. The correlation of seismic properties measured on borehole cores with surface seismic data can constrain the origin of this reflectivity. To this end, we compare seismic velocities measured on cores to in situ velocities measured in the borehole. For some intervals of the COSC-1 borehole, the core and downhole velocities deviate by up to 2 km s−1. These differences in the core and downhole velocities are most likely the result of microcracks mainly due to depressurization. However, the core and downhole velocities of the intervals with mafic rocks are generally in close agreement. Seismic anisotropy measured in laboratory samples increases from about 5 % to 26 % at depth, correlating with a transition from gneissic to schistose foliation. Thus, metamorphic foliation has a clear expression in seismic anisotropy. These results will aid in the evaluation of core-derived seismic properties of high-grade metamorphic rocks at the COSC-1 borehole and elsewhere.

New high-resolution 2D seismic imaging of fluid escape structures in the Makran subduction zone, Arabian Sea

ABSTRACT Seabed fluid escape is active in the Makran subduction zone, Arabian Sea. Based on the new high-resolution 2D seismic data, acoustic blanking zones and seafloor mounds are identified. Acoustic blanking zones include three kinds of geometries: Bell-shaped, vertically columnar and tilted zones. The bell-shaped blanking zone is characterized by weak and discontinuous reflections in the interior and up-bending reflections on the top, interpreted as gas chimneys. Vertically columnar blanking zone is interpreted as side-imaged gas chimneys associated with focused fluid flow and topped by a seafloor anomaly expressed as a localized reflection discontinuity, which may together serve as a vent structure. Tilted acoustic blanking zone could be induced by accretionary thrust activity and rapid sedimentation surrounding slope. Seafloor mounds occur at the sites of bell-shaped acoustic blanking zone and may be associated with the material intrusion. Bottom simulating refectors (BSRs) are widely distributed and exhibit a series of characteristics including diminished amplitude, low continuity as well as local shoaling overlapping with these acoustic blanking zones. The large amount of gases dissociated from the gas hydrates migrated upwards and then arrived at the near-seafloor sediments, followed by the formation of the gas hydrates and hence the seafloor mound.

Analyzing the architecture of point bar of meandering fluvial river using ground penetration radar: A case study from Hulun Lake Depression, China

The point bar is one of the most important reservoirs in a meandering depositional system, and accurately building a 3D architecture model for point bars is crucial to predict hydrocarbon distribution within the reservoir. Unfortunately, we can only obtain a qualitative description about the internal architecture of the point bar due to the limited information or the low resolution of available data (such as reflection seismic data). To build a 3D prototype point bar reservoir model, we analyze the architecture of point bars by integrating high-resolution ground penetrating radar (GPR) data and modern deposition. We found that our GPR data have five main reflection patterns (GPR facies), and GPR facies can be used to relate with architectural elements (the depositional facies and geobodies within depositional facies). The concave-down GPR facies is usually related to the abandoned channel. The continuous, subhorizontal, subparallel GPR facies is commonly related with lateral-accretion sand bodies within the point bar. The multiple stacked small-scale, discontinuous reflections GPR facies is interpreted to be shale drapes within the point bar. We further analyzed the geometry parameters of the identified channels. We found that the nonsymmetric [Formula: see text] of abandoned channel near the channel axis is related to the ratio between the curvature of channel radius [Formula: see text] and channel width [Formula: see text] ([Formula: see text]). Finally, we built two 3D channel reservoir models and our models could provide useful guidance for the architecture analysis of buried meandering fluvial reservoirs.

Gas occurrence and shallow conduit systems in the Western Sea of Marmara: a review and new acoustic evidence

Based on 3D and 2D high-resolution multichannel seismic reflection data in the Western High-Sea of Marmara, this study reviews shallow gas occurrence and related structures and classifies gas conduit systems within the upper, few hundred meter-thick sediment layers below the seafloor. Acoustic anomalies including high amplitude-reverse polarity reflections (bright spots), low amplitude transparent zones, chaotic or discontinuous reflections, pull-down effects, and plumes in the water column are interpreted in terms of natural gas occurrence and fluid flow structures (e.g., mud volcanoes, pockmarks). The gas occurrence is thought to be mostly of thermogenic origin. Mud volcanoes are one of the primary gas conduits forming craters on the seabed due to overpressure of fluidized gassy sediment flows. Following the reach of the Northern Branch of the North Anatolian Fault (NAF-N) to the Western High, the thermogenic fluids are believed to migrate vertically and horizontally to shallow depths mainly through the faults. Natural gas most probably originates from the Thrace Basin Eocene source rock or the Eocene-Oligocene reservoir rock, which extends below the Western High. Shallow gas is distributed by minor faults and gas pipes. Gas, to some extent, emanates from the seafloor via pockmarks and mud volcanoes or is trapped by the crests of the anticlines coinciding with erosional surfaces, impermeable sediments, and gas hydrate-bearing layers. Shallow traps below the tectonized “Western High” structure are likely located in thin layers of sands imbedded with impermeable silty clay layers. However, there is no shallow reservoir in the usual sense within the upper layers imaged by the 3D seismic data (< 300 ms two-way travel time). The existence of gas is an indicator of hydrocarbon-rich layers at depth and of active tectonics, and it also impacts the global climate and marine life conditions.

Seismic Facies Analysis for Lithofacies Prediction, Okam Field of Niger Delta, Nigeria

Seismic facies analysis constrained with well log information have been used to predict lithofacies distribution across the Okam Field of Niger Delta. Density and gamma ray logs were cross-plotted and the seismic section was subdivided vertically into different seismic facies. The delineated lithologies, from well logs were correlated with seismic facies signatures using lines of intersection across the wells. Gamma ray and resistivity logs were used to identify the interfaces between the lithofacies and correlated across the field. Structural interpretation was carried out. Time slices were generated and examined at different intervals within the identified reservoirs. Stratigraphic related attribute and envelope were extracted on these time slices. Three seismic facies type (facies A, B and C) were identified based on reflection amplitude, reflection patterns and continuity. Seismic facies A represents the undisturbed sediments in the Uppermost Benin Formation (parallel continuous, moderate to high reflections). Seismic facies B corresponds to the sand-shale pairs of the Agbada Formation which is diagnostic of moderate to high amplitude subparallel-parallel discontinuous reflections. The chaotic seismic facies signature (facies C) beneath this represents the overpressured mobile deformed Akata shales. The time slices show lateral variation in amplitude from high amplitude continuous reflections to low amplitude chaotic reflections from the southwest to northeast direction of the field. The extracted stratigraphic related attribute and envelope show lateral changes in amplitude from the northeast direction depicting increase in shaliness towards the northeast direction. The lateral variation in lithofacies across the field suggest varied and spatial changes in key reservoir parameters such as porosity and permeability that suggest changes in reservoir qualities across the field.

Role of short periodic orbits in quantum maps with continuous openings.

We apply a recently developed semiclassical theory of short periodic orbits to the continuously open quantum tribaker map. In this paradigmatic system the trajectories are partially bounced back according to continuous reflectivity functions. This is relevant in many situations that include optical microresonators and more complicated boundary conditions. In a perturbative regime, the shortest periodic orbits belonging to the classical repeller of the open map-a cantor set given by a region of exactly zero reflectivity-prove to be extremely robust in supporting a set of long-lived resonances of the continuously open quantum maps. Moreover, for steplike functions a significant reduction in the number needed is obtained, similarly to the completely open situation. This happens despite a strong change in the spectral properties when compared to the discontinuous reflectivity case. In order to give a more realistic interpretation of these results we compare with a Fresnel-type reflectivity function.

Tectono-Sedimentary Evolution of the Offshore Hydrocarbon Exploration Block 5, East Africa: Implication for Hydrocarbon Generation and Migration

Sedimentary deposits in Block 5, offshore Tanzania basin have been imaged using two-dimensional (2D) seismic data. The seismic data and well data reveal four tectonic units representing different tectonic events in relation to structural styles, sedimentation and hydrocarbon potential evolved in Block 5. Results show that during Early to Late Jurassic, Block 5 was affected by the break-up of Gondwana and the drifting of Madagascar as evidenced by patterns of sediments and structural features. The chaotic and discontinuous reflectors are characteristics features on the sediments pattern indicating a possible transitional setting following the breakup of Gondwana. From the Late Cretaceous, Block 5 sits in more stable subsiding sag as the consequence of the high thermal subsidence. The period displayed continuous parallel reflectors with few markable faults. This was followed by the late post rift sedimentation that occurred after Middle Eocene Unconformity characterized by high wavy and sub parallel reflectors. The evolution of Block 5 through major tectonic events reveals a more complete petroleum system towards the south. Thus, Block 5 responded in both space and time to a complex interplay between tectonics and sedimentation. This indicates that structural styles and associated features are potential control for hydrocarbon generation and migration.