Seismic Horizons Research Articles

Seismic horizon tracking using a deep convolutional neural network

Seismic horizons are essential for structural analysis, inversion, time-to-depth conversion, and seismic attribution analysis. However, seismic horizons are obtained commonly by manual tracking or a combination of manual tracking and traditional auto-tracking techniques, which is a time consuming and error-prone process. Although many conventional auto-tracking techniques have been proposed to improve the efficiency of horizon tracking, there are still many challenges to track seismic horizons with complex seismic reflection signatures. A deep convolutional neural network (CNN) method, a typical kind of deep neural networks in the field of deep learning, was proposed in this paper to solve the problems. Seismic horizon tracking is formulated as an image classification task. CNN can take full advantage of the high flexibility in network architecture and hierarchical feature extraction ability to track horizons from seismic volumes in which discontinuities, lateral variations and faults are apparent. We designed a CNN structure for horizon tracking and trained CNN models by using only 1% and 1.5% of the seismic volume to perform a single horizon and multiple horizon tracking. The root mean square error (RMSE) and the coefficient of determination (R2) between the horizon tracked by CNN model and the manual-tracking are 1.78 and 0.998 in single horizon tracking, respectively. The average RMSE and R2 are 2.68 and 0.992 in multiple horizon tracking, respectively. The research we have done suggests that the proposed method can track seismic horizons from 3-D seismic volumes much more accurately and efficiently than conventional methods.

Using recursive inversion as input for gross-rock volume extraction from lithology prediction volumes: How bad can it be?

SummaryReserves and Resources can be directly estimated by using seismic lithology prediction volumes generated from AVO inversion, calibrated to wells, to estimate sand rock volumes within a stratigraphic interval. However, high quality AVO inversion data and studies are not always available. This case study utilises recursive inversion to generate prediction cubes for input to geobody based gross rock volume estimates.Here, relative recursive inversions of the near and far seismic stacks are generated. EEI rotation theory was applied to calculate relative AI and Vp/Vs volumes. These have then been converted to band-limited absolute inversion volumes by adding a low frequency model built using seismic horizons, well logs and rock physics trends. Finally, probability density functions calibrated to wells were estimated to calculate lithology prediction volumes. A sand probability volume is then calculated using these probability density functions. A relative approach has not been applied due to poor separability of different lithologies in cross-plot space.This method is applied to an area where a single multiazimuth PSDM seismic survey covers two gas fields and several deep exploration prospects. However, previous inversion studies were limited to the individual fields (each inverted separately), incorporated fluid contact information and did not cover the deeper exploration, so were therefore considered sub-optimal.Although there is potential for results from this method to be “bad”, this case study was successful. The inversion volumes generated as part of this study enabled a wholistic view of the fields and exploration prospectivity, which had not been previously possible with the available QI volumes. The seismic data used for input was exceptionally good, and there was abundant well control to provide control and for use in blind testing. The amount of validation and quality-control applied to this project cannot be under-stated. It is critically important to be mindful of the limitations and broad assumptions that are applied as part of this work-flow. These include the addition of the low-frequency model, wavelet affects not being taken into account and depth decay of the lithology predictions due to the application of a single PDF.

Origin of seismic reflections in a carbonate gas field, Lower Miocene, offshore Myanmar

The geological origin of seismic reflections, within a carbonate gas reservoir, has been determined on the basis of an integrative analysis of cores, well-logs, pre-production and 4D time-lapse-seismic data. The gas reservoir is subdivided into meter to decameter-thick diagenetic units which are characterized by distinct acoustic properties. Low impedance units are dominant and consist of highly microporous and vuggy foraminiferal/coralline algal floatstones intervals whose porosity has been significantly enhanced in burial diagenetic environments. High to moderate acoustic impedance units (thickness: 1–20 m) are related to various depositional and diagenetic fabrics: 1) early-lithified coral floatstones, 2) foraminiferal rudstone whose intergranular space is occluded by shallow burial sparry calcite and 3) carbonate breccia with neomorphosed corals occurring below an intra-formational subaerial exposure surface. Within the gas zone, seismic reflection horizons may form at the boundary between two diagenetic units with contrasted acoustic impedance or may result from the interference between reflection at base and top of such intervals. A stratigraphy-cross-cutting reflection horizon has been shown to form at a major and laterally continuous shift in porosity which is related to a differential diagenetic evolution between the gas and the water zone, during or after hydrocarbon emplacement. Finally, the analysis of the geological origin of seismic reflections has been proved to help predicting and mapping the major heterogeneities with significant impact on flow during production.

A rock physics model to map gross lithology using compaction

ABSTRACTDifferential compaction has long been used by seismic interpreters to infer subsurface geology using knowledge of the relative compaction of different types of sediments. We outline a method to infer the gross fraction of shale in an interval between two seismic horizons using sandstone and shale compaction laws. A key component of the method involves reconstruction of a smooth depositional horizon by interpolating decompacted thicknesses from well control. We derive analytic formulae for decompaction calculations using known porosity–stress relations and do not employ discrete layer iterative methods; these formulae were found to depend not only upon the gross fraction of shale but also on the clay content of the shales and the thickness of the interval. The relative merits of several interpolation options were explored, and found to depend upon the structural setting. The method was successfully applied to an oil sands project in Alberta, Canada.

Automatic extraction of dislocated horizons from 3D seismic data using nonlocal trace matching

Extracting key horizons from seismic images is an important element of the seismic interpretation workflow. Although numerous computer-assisted horizon extraction methods exist, they are typically sensitive to structural and stratigraphic discontinuities. As a result, these computer-assisted methods have difficulties in extracting noncoherent dislocated horizons. We have developed a new data-driven method to correlate, track, and extract horizons from seismic volumes with complex geologic structures. Our method correlates seismic horizons across discontinuities and does not require user input in the form of seed points or prior identification of faults. Furthermore, the method is robust toward amplitude changes along a seismic horizon and does not jump from peak to trough or vice versa. We use a large sliding window and match full-length seismic traces using nonlocal dynamic time warping to extract grids of correlated points for our target horizons. Through computed accuracy measurements, we discard nonaccurate correlations before interpolating complete seismic horizons. Because our method does not require manually picked seed points or prior structural restoration, it does not rely on interpretive experience or geologic knowledge. The proposed method is applied on different real and complex seismic images, with two case examples from the southwestern Barents Sea, and one on the open source Netherlands F3 seismic data.

Semiautomated seismic horizon interpretation using the encoder-decoder convolutional neural network

The seismic horizon is a critical input for the structure and stratigraphy modeling of reservoirs. It is extremely hard to automatically obtain an accurate horizon interpretation for seismic data in which the lateral continuity of reflections is interrupted by faults and unconformities. The process of seismic horizon interpretation can be viewed as segmenting the seismic traces into different parts and each part is a unique object. Thus, we have considered the horizon interpretation as an object detection problem. We use the encoder-decoder convolutional neural network (CNN) to detect the “objects” contained in the seismic traces. The boundary of the objects is regarded as the horizons. The training data are the seismic traces located on a user-defined coarse grid. We give a unique training label to the time window of seismic traces bounded by two manually picked horizons. To efficiently learn the waveform pattern that is bounded by two adjacent horizons, we use variable sizes for the convolution filters, which is different than current CNN-based image segmentation methods. Two field data examples demonstrate that our method is capable of producing accurate horizons across the fault surface and near the unconformity which is beyond the current capability of horizon picking method.

Structurally tailored 3D anisotropic controlled-source electromagnetic resistivity inversion with cross-gradient criterion and simultaneous model calibration

Geologic interpretation of 3D anisotropic resistivity models from conventional marine controlled-source electromagnetic (CSEM) data inversion faces difficulties in low-resistivity contrast sediments and structurally complex environments that typify the new frontiers for hydrocarbon exploration. Currently, the typically reconstructed horizontal resistivity [Formula: see text] and vertical resistivity [Formula: see text] models often have conflicting depth structures that are difficult to explain in terms of subsurface geology, and the resulting resistivities may not be close to the true formation resistivities required for estimating reservoir parameters. We have investigated the concept that an objective geologically oriented or structurally tailored inversion can be achieved by requiring that the cross-product of the gradient of horizontal resistivity and the gradient of the vertical resistivity is equal to zero at significant geologic boundaries. We incorporate this boundary-shape criterion in our 3D inverse problem formulations, implemented within nonlinear model-space and conjugate-gradient contexts, for cases in which a priori calibration data from wells and/or seismically derived subsurface boundaries are available and for cases in which these are lacking. The resulting fit-for-purpose solutions serve to better analyze the peculiarity of a given data set. We applied these algorithms to synthetic and field CSEM data sets representing a fold-thrust environment with low-resistivity and low-contrast sediments. The resulting [Formula: see text] and [Formula: see text] models from cross-gradient joint inversion of synthetic data of appropriate frequency bandwidth without a priori information are structurally similar and consistent with the test models, whereas those from the inversions of band-limited field data are consistent with the available seismic and resistivity well-log data. This particular approach will thus be useful for lithologic correlation in frontier regions with limited a priori information using broadband CSEM data. For these band-limited field data, we found that the anisotropic bulk resistivities of the low-contrast sediments are better determined by incorporating a priori calibration data from triaxial resistivity logs and seismic horizons.

Pore Pressure Prediction in Onshore West Niger Delta Using Inverted Seismic Velocity and Derived Velocity (Vp) - Vertical Effective Stress (VES) Coefficients

In this study, pore pressure has been predicted using seismic data and derived compressional wave velocity (V p ) - Vertical Effective Stress (VES) coefficients. Post Stack Time Migration (PSTM), angle stack gathers, seismic horizons, checkshot, wireline logs, drilling and pressure data from six wells in the Onshore West Niger Delta, Nigeria were analysed and interpreted. Using generated velocity and density crossplots, the active overpressure generating mechanisms for the studied area were deduced. The V p -VES coefficients were modelled using the direct pressure data and the overburden profile computed from density log. Post stack seismic inversion was performed to improve the seismic resolution as well as derive acoustic impedance using well velocities and stacking velocities from velocity analysis of the 3-D seismic data. The derived V p -VES coefficients were used to transform the seismic acoustic impedance velocity into seismic pore pressure volume. Pore pressure profiles were accordingly extracted along well paths so as to test the accuracy of the model. Interpreted density-velocity crossplots revealed a decrease in velocity at constant density of 2.4 g/cc, an indication that unloading mechanisms contribute to overpressure in the field. The Bowers’ V p -VES coefficients of 7.43 and 0.77 were determined for A and B parameters respectively. Based on the results obtained, the top of overpressure occurred at a depth of 3750 ft and 3800 ft in UMO-001 and UMO-002 wells respectively with a corresponding average pore pressure gradient of 0.47 psi/ft for both wells, indicating that the wells are mildly overpressured. Onsets of unloading were observed in UMO-001 and UMO-002 wells at depths of 6250 ft and 6800 ft with pore pressure gradients of 0.51 psi/ft and 0.60 psi/ft respectively. The Derived Seismic Pore Pressure (DSPP) matched the measured pressure value (kick) of 5300 psi at a depth of 7450 ft and this validated and further increased confidence on the values of the V p -VES coefficients derived. These results show that the derived seismic acoustic impedance volume, vertical effective stress and overburden model produce high resolution seismic pore pressure cube in both time and space. The derived models when applied especially, with seismic acoustic impedance volume can be used to plan and drill future wells with great successes in the studied area. Keywords: pore pressure, vertical effective stress, seismic velocity, acoustic impedance DOI : 10.7176/JEES/9-10-07 Publication date :October 31 st 2019

Estimating sedimentary thickness of Lanka Basin using digitised scanned seismic sections

In exploration geophysics, seismic surveys and their interpretations provide the most reliable information of the subsurface structures. Extensive work on the determination of the subsurface structure has been carried out in both Cauvery and Mannar basins of offshore Sri Lanka. Freely available satellite- gravity and magnetic data suggest that the Lanka Basin may have the necessary sediment volume for the occurrence of hydrocarbons. However, without seismic data, this suggestion cannot be tested further. As an alternative to acquiring additional seismic data in the region, this research focused on digitising 50,000 km of vintage seismic lines from the National Geophysical Data Centre (NGDC) data repository and converting them into Seg-Y format. Key seismic horizons on the digitised sections were interpreted to provide details of the seabed and acoustic basement in the time domain. Regional sedimentary thickness maps were compiled in the time domain interpolating the interpreted horizons using ‘kriging’ method. The velocity data acquired in the region were used to convert the maps from time to depth domain. The results indicate that average thickness of sediments in the region varies around 5000 m to 6000 m, where the maximum thickness is around 8000 m in the North Eastern part of the Lanka basin. The thickness maps can be used as a reference dataset to plan commercial seismic surveys in the future for hydrocarbon exploration in the Lanka Basin.

Spectral structure-oriented filtering of seismic data with self-adaptive paths

We have developed an algorithm to perform structure-oriented filtering (SOF) in 3D seismic data by learning the data structure in the frequency domain. The method, called spectral SOF (SSOF), allows us to enhance the signal structures in the [Formula: see text]-[Formula: see text]-[Formula: see text] domain by running a 1D edge-preserving filter along curvilinear self-adaptive trajectories that connect points of similar characteristics. These self-adaptive paths are given by the eigenvectors of the smoothed structure tensor, which are easily computed using closed-form expressions. SSOF relies on a few parameters that are easily tuned and on simple 1D convolutions for tensor calculation and smoothing. It is able to process a 3D data volume with a 2D strategy using basic 1D edge-preserving filters. In contrast to other SOF techniques, such as anisotropic diffusion, anisotropic smoothing, and plane-wave prediction, SSOF does not require any iterative process to reach the denoised result. We determine the performance of SSOF using three public domain field data sets, which are subsets of the well-known Waipuku, Penobscot, and Teapot surveys. We use the Waipuku subset to indicate the signal preservation of the method in good-quality data when mostly background random noise is present. Then, we use the Penobscot subset to illustrate random noise and footprint signature attenuation, as well as to show how faults and fractures are improved. Finally, we analyze the Teapot stacked and depth-migrated subsets to show random and coherent noise removal, leading to an improvement of the volume structural details and overall lateral continuity. The results indicate that random noise, footprints, and other artifacts can be successfully suppressed, enhancing the delineation of geologic structures and seismic horizons and preserving the original signal bandwidth.

(ChinaVis 2019) uncertainty visualization in stratigraphic correlation based on multi-source data fusion

As a most important step in geological interpretation, stratigraphic correlation plays important roles in reservoir estimation and geologic modeling. A variety of datasets are used for stratigraphic correlation, such as well-logging data and seismic data, which are collected by different kinds of sensors. However, much uncertainty will be generated in the traditional course of stratigraphic correlation, because the complex underground geological structures cannot be comprehensively depicted by single dataset. Therefore, in this paper, we propose a visualization system to present and reduce the uncertainty in stratigraphic correlation based on the fusion analysis of multi-source datasets. First, a synthetic seismogram is modeled for each drilling well and a traditional time-depth conversion is conducted to match the seismic data and logging data. Then, an uncertainty model is proposed to quantify the depth difference between seismic horizons and stratigraphic structures extracted from different datasets. Furthermore, a set of visual designs are integrated into an uncertainty visualization system, enabling users to conduct intuitive uncertainty exploration and supervised optimization of stratigraphic correlation. Case studies based on real-world datasets and interviews with domain experts have demonstrated the effectiveness of our system in analyzing the uncertainty of stratigraphic correlation and refining the results of geological interpretation.

Impact of the East African Rift System on the routing of the deep‐water drainage network offshore Tanzania, western Indian Ocean

AbstractThe East African Rift System (EARS) exerted a major influence on river drainage basins and regional climate of east Africa during the Cenozoic. Recent studies have highlighted an offshore branch of the EARS in the western Indian Ocean, where the Kerimbas Graben and the Davie Ridge represent its sea floor expression. To date, a clear picture of the impact and timing of this EARS offshore branch on the continental margin of the western Indian Ocean, and associated sediment dispersal pathways, is still missing. This study presents new evidence for four giant canyons along the northern portion of the Davie Ridge offshore Tanzania. Seismic and multibeam bathymetric data highlight that the southernmost three canyons are now inactive, supra‐elevated relative to the adjacent sea floor of the Kerimbas Graben and disconnected from the modern slope systems offshore the Rovuma and Rufiji River deltas. Regional correlation of dated seismic horizons, integrated with well data and sediment samples, proves that the tectonic activity driving the uplift of the Davie Ridge in this area has started during the middle‐upper Miocene and is still ongoing, as suggested by the presence of fault escarpments at the sea floor and by the location and magnitude of recent earthquakes. Our findings contribute to placing the Kerimbas Graben and the Davie Ridge offshore Tanzania in the regional geodynamic context of the western Indian Ocean and show how the tectonics of the offshore branch of the EARS modified the physiography of the margin, re‐routing the deep‐water drainage network since the middle Miocene. Future studies are needed to understand the influence of changing sea floor topography on the western Indian Ocean circulation and to evaluate the potential of the EARS offshore tectonics in generating tsunamigenic events.

Analysis of active faults based on natural earthquakes in Central north China

As an important part of the integration of Beijing-Tianjin-Hebei, it is very important to analyze the seismic activity of active structures in Central north China. There are two sets of active faults belt in the lot, and there have been devastating earthquakes, which need to grasp the level of seismic activity. Located at the boundary of the third-order tectonic unit, there are a series of faults in the area, such as the north to the east Taihang mountain front fault, the north to the east Xinhe fault and the north to the west Cixian-daming fault, which intersect and cut each other to form fault depression basin. There are different scales of NE, NNE, and NW faults, which are considered to be the birthplace of the earthquake. At the same time, more than 6 magnitude earthquake magnitude have happened in the Cixian and Xingtai. The seismogenic structure of the research shows that these earthquakes associated with deep fault activities, the source location in the deep crust velocity structure mutation. In order to determine and analyze the P-wave velocity structure characteristics and the hypocenter distribution, and the activity characteristics of the deep space of active fault belt, the natural seismic data monitored by seismic network are collected and organized, which are used to analyze the relationship between seismic wave velocity and hypocenter position. Due to the deep migration of the crustal material and the horizontal principal compressive the NEE direction stress in North China, the crustal thickness on the west side of the Taihang mountain front fault is greater than that of the east side, from 1 km to 7 km. Along the trend, the epicenter of the small earthquake is mainly distributed in the crustal thickening area on the west side of this active fault, and the epicenter of the eastern plain is less distributed. The depth of the small earthquake is concentrated in the range of 8–20 Km. Comprehensive analysis shows that the seismic p-wave velocity structure characteristics can be divided into the sedimentary cover, upper crust, the earth's crust and the lower crust structure, thickness of different location have change, the thickness of the sedimentary cover Taihang uplift zone thickness 0.1–3 km, to 5–7 km in Handan fault depression; The thickness of the crystalline basement in the Taihang mountain uplift is 3–5 km, and the Handan fault depression basin is thickened to 7–10 km. The thickness of the crust on the west side of Taihang mountain front fault is significantly greater than that on the east side. The thickness of the crust on the west side is decreased from 36–40 km on the west side to 30–35 km on the east side and about 7–10 km on the east side. Due to the near east-west tension, the zone has disengaging movement, forming the characteristics of shovel-type normal fault combination. In the earth's crust with high-speed and low-speed layer between configuration characteristics, seismic horizon of earthquake preparation 12–18 km deep in the earth's crust, characterized by low speed and high speed layer mutation position, concentrated distribution of small earthquakes, the seismogenic layer a concentration distribution in the crust velocity structure conversion section. Seismic activity is concentrated in the west end of the Cixian-daming fault and the west side of the Xinhe fault, with an average depth of 12–18 km.

Full-volume 3D seismic interpretation methods: A new step towards high-resolution seismic stratigraphy

Following decades of technological innovation, geologists now have access to extensive 3D seismic surveys across sedimentary basins. Using these voluminous data sets to better understand subsurface complexity relies on developing seismic stratigraphic workflows that allow very high-resolution interpretation within a cost-effective timeframe. We have developed an innovative 3D seismic interpretation workflow that combines full-volume and semi-automated horizon tracking with high-resolution 3D seismic stratigraphic analysis. The workflow consists of converting data from seismic (two-way traveltime) to a relative geological time (RGT) volume, in which a relative geological age is assigned to each point of the volume. The generation of a horizon stack is used to extract an unlimited number of chronostratigraphic surfaces (i.e., seismic horizons). Integrated stratigraphic tools may be used to navigate throughout the 3D seismic data to pick seismic unconformities using standard seismic stratigraphic principles in combination with geometric attributes. Here, we applied this workflow to a high-quality 3D seismic data set located in the Northern Carnarvon Basin (North West Shelf, Australia) and provided an example of high-resolution seismic stratigraphic interpretation from an Early Cretaceous shelf-margin system (Lower Barrow Group). This approach is used to identify 73 seismic sequences (i.e., clinothems) bounded by 74 seismic unconformities. Each clinothem presents an average duration of approximately 63,000 years (fifth stratigraphic order), which represents an unprecedented scale of observation for a Cretaceous depositional system on seismic data. This level of interpretation has a variety of applications, including high-resolution paleogeographical reconstructions and quantitative analysis of subsurface data. This innovative workflow constitutes a new step in seismic stratigraphy because it enables interpreters to map seismic sequences in a true 3D environment by taking into account the full variability of depositional systems at high frequency through time and space.

Multiresolution neural networks for tracking seismic horizons from few training images

Detecting a specific horizon in seismic images is a valuable tool for geologic interpretation. Because hand picking the locations of the horizon is a time-consuming process, automated computational methods were developed starting three decades ago. Until now, most networks have been trained on data that were created by cutting larger seismic images into many small patches. This limits the networks ability to learn from large-scale geologic structures. Moreover, currently available networks and training strategies require label patches that have full and continuous horizon picks (annotations), which are also time-consuming to generate. We have developed a projected loss function that enables training on labels with just a few annotated pixels and has no issue with the other unknown label pixels. We use this loss function for training convolutional networks with a multiresolution structure, including variants of the U-net. Our networks learn from a small number of large seismic images without creating patches. Training uses all seismic data without reserving some for validation. Only the labels are split into training/testing. We validate the accuracy of the trained network using the horizon picks that were never shown to the network. Contrary to other work on horizon tracking, we train the network to perform nonlinear regression, not classification. As such, we generate labels as the convolution of a Gaussian kernel and the known horizon locations that communicate uncertainty in the labels. The network output is the probability of the horizon location. We examine the new method on two different data sets, one for horizon extrapolation and another data set for interpolation. We found that the predictions of our methodology are accurate even in areas far from known horizon locations because our learning strategy exploits all data in large seismic images.

3-D structural and seismic attribute analysis for field reservoir development and prospect identification in Fabianski Field, onshore Niger delta, Nigeria

An integrated 3-D seismic data, suite of eleven well logs and checkshot data from Fabianski field, Coastal Depobelt, Niger Delta basin Nigeria were analysed and interpretations carried out using relevant algorithm models in the Petrel workstation for detailed 3-D structural and seismic attribute analysis. The method adopted involves well log interpretation for identification of reservoirs tops and base, well correlation for determination of lateral continuity of the reservoirs, seismic structural mapping, seismic attribute analysis, lead(s)/prospect(s) mapping and risk assessment. Twenty-three (23) faults were interpreted to offset the stratigraphic packages within the field at different seismic horizons. These faults created structures that are favourable for hydrocarbon trapping and accumulation. Three reservoirs have been identified: FAB-1, FAB-2 and FAB-3. Correlation of the reservoirs across five wells along depositional dip shows that the reservoirs are laterally continuous with varying thicknesses at well points. FAB-1 reservoir was studied in detail because it corresponds to a seismic flat spot identified in seismic volume. Four prospects were identified within the FAB-1 reservoir based on structural contour closures: FAB-1 southern prospect, FAB-1 northern prospect, FAB-1 northeastern prospect and FAB-1 northwestern prospect. Only FAB-1 southern prospect shows evidence of hydrocarbon accumulation. FAB-1 southern reservoir is characterized by localized bright amplitudes of root mean square (RMS) and envelope attributes which indicates porous and fluid filled lithologies; constant drop-off high frequencies of instantaneous frequency (12 Hz–25 Hz), and very bright localized high values of sweetness attribute indicative of hydrocarbon saturated sand. Positive values of apparent polarity attribute validate the presence of hydrocarbons in the southern prospect. Spectral decomposition analysis shows that the FAB-1 southern reservoir is better imaged by a frequency range of 15 Hz–25 Hz. It is therefore concluded that spectral decomposition techniques integrated with seismic attributes can unravel subtle indications that are not independently conclusive, and delineate hydrocarbon charged reservoir geometry and structural discontinuities within complex tectonic settings.

Oscillations of global sea-level elevation during the Paleogene correspond to 1.2-Myr amplitude modulation of orbital obliquity cycles

The mechanisms involved in the formation of 1- to 2-Myr-long third-order stratigraphic sequences through the Phanerozoic have been extensively debated, but the main underlying forcings remain uncertain. In this study, we investigated third-order sequences of Paleocene-Eocene age in the East China Sea Shelf Basin, identifying a prominent ∼1.2-Myr periodicity in the 405-kyr-tuned gamma ray profile of the WP-1 borehole. We infer that this ∼1.2-Myr cycle, which corresponds to long-period amplitude modulation of obliquity, was the main driver of third-order sea-level changes and sequence development. This modulation entails variation in the range of obliquity amplitude between a maximum of 2.4° (i.e. 24.5°–22.1°) and a minimum of 0.3° (i.e. 23.3°–23.0°) as a result of interactions among the three primary parameters of Earth's orbit (i.e., eccentricity, obliquity, and precession). We anchored our floating astronomical time scale (ATS) to the T42 seismic horizon, a major sequence boundary between the Lin Feng and Mingyuefeng formations that corresponds to the top of Nannofossil Zone NP8 (reported age of 57.7 Ma). This yields a fixed ATS for the late Paleocene-to-middle Eocene interval spanning 60.84 to 48.71 Ma. Finally, we evaluated our findings relative to the third-order sequence stratigraphy of the East China Sea Shelf Basin and to records of early Cenozoic eustasy and global events.

Seismic delineation and well logging evaluation for albian Kharita Formation, South West Qarun (SWQ) field, Gindi Basin, Egypt

The present work focuses on the integration between seismic and well log interpretations for evaluating the sandstone of Albian Kharita Formation in the southwest Qarun Field, Gindi Basin, Western Desert, Egypt. The applied methods in the present work include; seismic interpretation for the Kharita Formation and mapping its corresponding seismic horizon over the study area. This step has been followed by qualitative and quantitative well logging data interpretations for the entire sandstone of the Kharita Formation within South West Qarun Field. The time structure map on top of the Kharita Formation in the study area within the Gindi Basin has revealed NE-SW trending anticline plunge toward the NE. This anticline bounded and intersected by two NE-SW reverse faults. This compressional feature was formed during the Late Cretaceous tectonic inversion which resulted as a response to the NW movement of the African Plate relative to Laurasia Plate. The interpreted anticline probably creates a structural closure for hydrocarbon accumulation in the study area. Through qualitative and quantitative interpretation of the well log data, the sandstones of the Kharita Formation in the southwest Qarun Field display good reservoir characteristics with high potential for oil production in its uppermost part (zone I) with net pay thickness equals 36 ft. This reservoir possesses shale volume lower than 11%, low water saturation values varies between 18 and 46%, effective porosity ranges between 10 and 14%, low Bulk Volume of Water (BVW) < 0.05, irreducible water saturation varies between 16 and 22%, and permeability varies between 6 and 56 MD. Since the water saturation values in the zone I are below the critical water saturation (Scw = 47%), it is expected that the whole zone will transmit hydrocarbon at valuable rate.

Deposition and sea-level evolution models for Upper Pleistocene/ Holocene in the São Sebastião Channel (SE Brazilian coast) inferred from 5th order seismic stratigraphy

In this paper, we used seismic stratigraphy for the study of deposition and sea-level evolution on the São Sebastião Channel (SSC), southern Brazilian coast. About 60 km of high-resolution single-channel seismic lines were acquired to establish a 5th order seismic stratigraphy model for the area. After graphical processing for noise attenuation and enhancing of deep-reflections, we could interpret six seismic horizons and the acoustic basement which together defined six seismic units. Studying those units in a late Quaternary relative sea-level oscillations context, we propose a 4-phase deposition evolution model that took place since the Marine Isotopic Stage (MIS) 5e in the SSC area. The first phase comprises the deposition of seismic units U1 and U2 prior to MIS 4 with the deposition of one lowstand systems tract (LST) and one highstand systems tract (HST). Before the second phase, the sea-level dropped eroding the top layers of the previous units. During the second phase, after the Last Glacial Maximum (LGM), another LST (unit U3) was formed in one of the three stabilization periods of Upper Pleistocene/early Holocene sea-level rise on the Brazilian coast. Following an increase in sea-level rise velocity, we interpreted a transgressive system tract (unit U4) and another HST (unit U5) developed until the maximum sea-level of the Mid-Holocene, at 6 ky B.P during the third phase of our model. During the fourth phase, sea-level fall evolved to the present level, giving conditions to the deposition of the last HST (unit U6) interpreted in the region.

Western Davis Strait, a volcanic transform margin with petroliferous features

Abstract We present a compilation of the western Davis Strait region offshore southeastern Baffin Island, Nunavut, Canada with new subsurface geological structural details and observations regarding past hydrocarbon occurrences from scientific and commercial exploration. This consists of seismic mapping with archival data correlated with a filtered marine Bouguer anomaly gravity compilation and magnetic data sets covering northern Saglek Basin, the western part of the Lady Franklin Basin and the Ungava Fault Zone from south of Baffin Bay. A regional seismic horizon for mapping basin architecture comes from the top of the Paleogene volcanic syn-magmatic zone, where pervasive volcanic flows and intrusions are intermingled with the sedimentary section. The seismic depth map to the top of the regional volcanic seismic horizon shows pre-rift sedimentary basins having maximum depths of approximately 4–5 km flanking the shallower Ungava Fault Zone. Correlation of Bouguer anomaly gravity and magnetic data interpretations with the seismic mapping, indicate that over some areas true crystalline basement is deeper than can be determined by reflection seismic, as the base of the syn-magmatic section is not resolvable for seismic mapping. Extensive Paleogene mafic intrusives and extrusive basalts dominate the architecture of this volcanic rifted margin as seen by the dominant high amplitude magnetic anomalies associated with many deeper structures. The over 250 km long Davis Strait Fault is recognised as the key structural element of the Ungava Fault Zone (UFZ) and valley complex. The adjoining Davis Strait High maps on seismic as a continuous structure running the length of Davis Strait plunging southwards to a Bouguer gravity high feature that terminates the western end of the extinct Eocene spreading zone south of Davis Strait. This horn shaped structural feature establishes the presence of an accommodation zone with multiple faults and localised thrust faulting as required to fit the complex mechanics for strike-slip motion that occurs along the south end of this transform fault system. The revised marine Bouguer anomaly gravity data set also defines two new, near shore grabens east of Cumberland Sound, the southern Tariut Basin and the northern Imaqpik Basin, each extending over 100 km in length with sediment thicknesses of at least 4 km. These pre-rift basins most likely originate from the Paleozoic based on seafloor dredge and nearby shallow drill cores from previous studies. The hydrocarbon charge of a previously unexplained petroliferous shallow marine drill core that is adjacent the eastern edge of the Tariut Basin is attributed to Paleozoic source rocks that have undergone enhanced thermal maturation from sill intrusion associated with rifting. The Imaqpik Basin shows strong evidence of a hydrocarbon system from the proximity of clustered interpreted sea surface oil slicks, mapped from satellite radar images, and a local zone of anomalously high dissolved methane measured within the water column that originates from the seafloor immediately east of Cape Dyer at the northern limit of that basin. The overlying Cape Dyer flood basalt field extends from limited onshore exposures into the offshore and maps with magnetic data over an area of approximately 13,000 km2. This extrusive feature and it's implicit underlying intrusive components are likely the unconventional heat source for the anomalous enhanced thermal maturation of Paleozoic to Paleogene source rocks in these pre-rift basins that host this previously unrecognised petroleum system.