Good Lateral Continuity Research Articles

Enhancing magnetic source edges using the tilt angle of the analytic‐signal amplitudes of the horizontal gradient

AbstractEnhancing magnetic data is often complicated due to the non‐vertical orientation of the geomagnetic field and the orientation of remanent source magnetization. The complication can be reduced by reducing the data to the pole (mathematically making the geomagnetic field vertical), but this reduction process is problematic. The analytic‐signal amplitude can be used to enhance the edges of two‐dimensional sources without a reduction to the pole. However, the shape of the analytic‐signal amplitude is weakly dependent on the magnetization direction for grid data. This study presents an improved technique, namely the tilt angle of the analytic‐signal amplitudes of the horizontal gradient of the vertical integral. This quantity is also only weakly dependent on the magnetization direction and outlines the edges as well or somewhat better than other methods. It also implicitly involves second derivatives of the magnetic field, and we use synthetic data to demonstrate that noise is not amplified as much as it is when using other edge enhancement techniques that implicitly use second derivatives. A dataset of the Apiaí Terrane, Brazil, shows good lateral continuity of features compared with other edge‐enhancement methods, and subtle features like faults are easier to identify in the images generated by our new method. Upward continuation of the field, which is normally required, was not necessary to reduce the impact of noise on this field example.

Deep learning for high-resolution multichannel seismic impedance inversion

Seismic impedance inversion can obtain subsurface physical properties and plays an important role in hydrocarbon and mineral exploration. Due to the inaccurate and insufficient seismic data, the inverse problem is ill posed as characterized by unreliability and nonuniqueness of solutions. Regularization techniques relying on certain prior information often are introduced to force the inverse problem to obtain stable results with predetermined characteristics. However, for complex geologic conditions, these methods usually have difficulty achieving satisfactory accuracy and resolution. We develop a deep-learning (DL)-based multichannel impedance inversion method that flexibly incorporates prior information by training with numerous realistic structural 2D impedance models based on the features of field data. The DL framework is supplemented by the attention mechanism and residual block to automatically learn more features and details from training data. A novel hybrid loss function, combining [Formula: see text] loss and multiscale structural similarity loss, is introduced to enhance the network’s capacity for learning structural features. Synthetic and field data examples demonstrate that our method can effectively produce inversion results with high resolution, good lateral continuity, and enhanced structural features compared with traditional methods.

Borehole-driven sparse-spike deconvolution and seismic bandwidth enhancement

Reflectivity estimation approaches are usually driven solely by observed seismic data, leaving other types of a priori information, such as well-log data, out of the equation. This may result in solutions that honor the observed data but are not properly linked to geology. We provide a method for estimating sparse-spike reflectivity solutions that takes into account the observed data and any given sparse-spike model derived from well-log data. Starting with the well-log measurements, we estimate the reflectivities trace by trace by iteratively perturbing the previous solution with a warping function. This procedure is repeated until the synthetic trace formed by convolving with an appropriate wavelet fits the observed data. The assumption that two consecutive reflectivities have the same number of spikes with similar amplitudes and positions ensures lateral continuity. Because it is expected that reflectivity fluctuates smoothly from trace to trace, the technique is appropriate for areas with low to moderate structural complexity. The resulting sparse-spike reflectivity section can be considered as a product in and of itself. Even so, the interpreter might prefer a borehole-consistent frequency-enhanced seismic image, which can be easily produced by convolving the reflectivity with a suitable broadband wavelet. We rigorously test the technique on 1D and 2D synthetic data as well as on a 3D poststack field data set. The results indicate that we can obtain sparse-spike reflectivities with good lateral continuity that honor the observed data. Most importantly, the resulting reflectivity section (or frequency-enhanced data) is guaranteed to honor the well-log information too, which may aid users in seismic data analysis and interpretation.

Absorption Attenuation Compensation Using an End-to-End Deep Neural Network

Absorption attenuation compensation is an important part of seismic data processing. It enhances the resolution of non-stationary seismic data by compensating the amplitude energy and correcting phase distortion. The stabilized inverse <i>Q</i> -filter method, a widely used attenuation compensation method, constructs compensation operators based on stratigraphy-related assumptions and compensates seismic data using time-window analysis, which is computationally complex and sensitive to noise. The essence of attenuation compensation lies in the establishment of a nonlinear mapping relationship between attenuated and non-attenuated seismic traces, which strongly benefits from deep learning. This paper proposes a new method for attenuation compensation based on an end-to-end deep neural network to reduce the hand-crafted step of time-window analysis. Instead, the convolutional blocks of the network automatically learn and process seismic data features to achieve simultaneous amplitude and phase compensation. We have constructed two end-to-end network architectures for attenuation compensation: a fully convolutional network (FCN) and a U-Net. As an effective spectrum-broadening method, the compensation method based on the U-Net is shown to enhance vertical resolution with good lateral continuity, to provide reliable compensation results without complex calculations, and to exhibit high noise robustness. Synthetic data tests indicate that the compensation results from the U-Net are better than those from either the FCN or the stabilized inverse <i>Q</i> -filter method at different noise levels. Moreover, the correlation coefficient between the U-Net compensation results of the synthetic profile and the reference non-attenuated profile is higher than that of the FCN and the stabilized inverse <i>Q</i> -filter method. A field data application further verifies the effectiveness of this method.

Compact Smoothness and Relative Sparsity Algorithm for High-Resolution Wavelet and Reflectivity Inversion of Seismic Data

Wavelet and reflectivity inversion (WRI) is an important issue in seismic data processing. To overcome the ill-posedness of WRI inversion with more efficient parameter selection and better lateral continuity of reflectivities, we propose a new WRI algorithm named compact smoothness and relative sparsity (CSRS) algorithm, where a normalized compact constraint and a normalized smooth regularization is proposed for the wavelet inversion, and a relative sparsity constraint is proposed for the reflectivity inversion. The proposed constraints and regularization make the parameters of WRI easy to be selected. The proposed relative sparsity constraint can lead to a reflectivity profile with good lateral continuity as it can be suitable for various seismic data with a fixed sparsity parameter. We also propose an efficient algorithm for solving corresponding WRI optimization problem. The whole WRI problem is divided into reflectivity inversion subproblem and wavelet inversion subproblem by using alternating iterative method, where the initial wavelet is estimated by smoothing the absolute amplitude spectrum of averaged seismic data. The proximal algorithm is applied to solve both reflectivity inversion subproblem and wavelet inversion subproblem. By replacing Toeplitz matrix multiplication with fast Fourier transform (FFT) and using compact wavelet, our algorithm can be efficient for 3D seismic data. The numerical examples on 2D synthetic data, 2D offshore field data and 3D onshore field data demonstrate that, compared to Toeplitz-sparse matrix factorization (TSMF) algorithm, the CSRS algorithm with fixed default parameters can get high-resolution reflectivities with better lateral continuity, and requires much less computational time.

Geochemical Assessment and Lateral Reservoir Continuity of Asmari Reservoir Oils in the Cheshmeh‐Khush Oilfield, SW Iran

AbstractA total of 6 oil samples were systematically selected from six Asmari Reservoir wells in the Cheshmeh‐Khush Oilfield for geochemical evaluation of the hydrocarbon system, based on reservoir geochemistry and oil fingerprints. An investigation of the distribution patterns of normal alkanes and tricyclic and tetracyclic terpanes along with characteristic biomarkers of the depositional environment and sedimentary facies, indicated that the source rock of the studied hydrocarbons was deposited in a reducing aquatic environment with a low input of terrigenous material and predominantly carbonate lithology derived from organic algal matter. The studied oil samples exhibited moderate maturity, as was further confirmed by the parameters extracted from the light hydrocarbons. Statistical clustering based on different biomarker parameters indicated the presence of two oil families. Additionally, the application of branched and cyclic compounds in the light hydrocarbons (C5–C11) to evaluate lateral continuity of the Asmari reservoir further supported the presence of the two oil families. Other evidence proved the presence of a NE–SW trending fault separating wells X5 and X6 from the other wells in the field. In other wells across the field, good lateral reservoir continuity was observed, despite the presence of faults on the northern and southern plunges of the structure.

Increasing the accuracy of estimated porosity and saturation for gas hydrate reservoir by integrating geostatistical inversion and lithofacies constraints

Abstract Porosity, saturation, thickness of gas hydrate-bearing layers and their spatial distributions are key factors for production tests. The gas hydrate-bearing layers ranging from a few to tens of meters thickness are confirmed by Logging While Drilling (LWD) data and core samples at Sites W11 and SC-03, in the Shenhu area, South China Sea. Gas hydrate-bearing layers of two wells (about 200 m) show that not all layers exhibit good lateral continuity. Several thin layers (~4 m) with low gas hydrate saturations (15–20% of the pore space) or non-gas hydrate are laterally discontinuous. The interbedding of gas hydrate-bearing and non-hydrate layers with different saturations, thickness and random distribution cause the heterogeneities in the reservoir. The gas hydrate saturation and distribution inverted from deterministic and traditional geostatistical inversion have high uncertainties due to the limitations of the empirical relationship and probability density functions (PDFs). A better understanding of spatial distribution and saturation for each gas hydrate layer is useful to build a realistic net hydrate pay and resource estimation. In this study, we first divide gas hydrate saturations, porosity, acoustic impedance into low and high values based on the estimated LWD results, which is call as lithofacies. Then, we propose to create multivariate PDFs by lithofacies constraints. The acoustic impedance, saturation, thickness, porosity of gas hydrate-bearing layers and non-gas hydrate layers are inverted by displaying geostatistical inversion with lithofacies constraint. We found the spatial variations and heterogeneous distributions with a thickness ranging from 4 to 35 m and the laminated gas hydrate layers with saturations ranging from 10% to 40% are clearly shown from seismic data, which are useful for the horizontal well development method of a hydrate production test.

High-resolution reflectivity inversion based on joint sparse representation

High-resolution reflectivity inversion is termed as a fundamental yet essential step for the prediction of thin-bedded hydrocarbon reservoirs. However, algorithms suffer from two key issues: (1) seismic inversion is an ill-posed problem that has multiple solutions, and the results of trace-by-trace seismic inversion are quite poor in lateral continuity, and (2) algorithm stability is likely to be decreased owing to the noise and distortion associated with the acquisition and processing flows. In the current article, we formulate a new joint sparse representation through the combination with L2,1-norm misfit function, which possesses superior noise robustness, in particular in the presence of outliers. On the basis of the L2,1-norm regularization, this specific approach enforces a common sparsity profile, together with consistently lowering the multiplicity of solution. Subsequent to that, the resultant algorithm is applied to the multi-trace seismic inversion. Besides, the wedge model trial and practical applications suggest that the proposed inversion algorithm is stable, in addition to having good noise robustness and lateral continuity; moreover, the vertical resolution of λ/8 is realized under the noise and outliers interference. The logging data calibration illustrates that the proposed methodology is accurate and credible.

Petrophysical properties of heavy oil-bearing carbonate rocks and their implications on petroleum system evolution: Insights from the Majella Massif

Abstract In this work, we investigate the role of hydrocarbons in changing the petrophysical properties of rocks by merging laboratory measurements, outcrops characterization, and subsurface data focusing on a carbonate-bearing reservoir (Bolognano Formation) of the Majella massif. This reservoir represents an interesting analogue for subsurface carbonate reservoirs and is made of high porosity (up to 32%) ramp calcarenites saturated by hydrocarbon in form of bitumen. We have characterized in the laboratory density, porosity, compressive strength, Young's modulus and Poisson's ratio of both clean and heavy oil-bearing carbonate rocks of the Bolognano Formation. At ambient pressure the Vp are in the range of 3.49 km/s to 5.06 km/s for clean samples with an inverse relation with porosity, whilst the Vp range for HHC-bearing rocks are from 3.56 km/s to 4.56 km/s without any relation with measured porosity. These data show that porosity and presence of HHCs within the samples both affects seismic waves velocity. In particular, Vp and the derived dynamic Young's modulus generally strongly decrease with increasing porosity for clean samples and, for a fixed porosity, tends to increase with the presence of heavy-oil. This is confirmed also at higher (up to 100 MPa) confining pressure that has not a significant effect on Vp and Vs. Cyclic loading-unloading experiments show that the average compressive strength is 25 MPa and 38 MPa and average static Young's modulus are 5.7 GPa and 9.9 GPa, for clean and HHC-bearing samples respectively. Additionally, the permanent strain is always larger for clean samples. Field work, consisting in measuring fracture orientation in 11 outcrops of the same lithology, shows that both heavy oil-bearing and clean outcrops are characterized by two main trends NW-SE and NNE-SSW. However, the spacing data show that heavy-oil-bearing outcrops are much less fractured respect to clean outcrops. This suggests, assuming that the deformation occurred under the same stress state, that heavy oil-bearing outcrops are stiffer respect to clean outcrops, as supported by the laboratory measurements. We thus infer that in the study area hydrocarbons migration predates the last stage of deformation, limiting the fracturing in bitumen-bearing portions of the Bolognano Formation. At regional scale, the presence of buried oil fields located few kilometres away from the heavy-oil-bearing outcrops and pertaining to the same petroleum system, suggests a good lateral continuity of the reservoir giving clues about the key role played by primary porosity in the secondary migration that acted in this area.

The stratigraphic significance of paralic deposits in the Precipice–Evergreen succession, Surat Basin, Queensland

The Precipice Sandstone and Evergreen Formation in the Surat Basin, Queensland, are being examined as a reservoir-seal option for future geosequestration of CO2. Effective reservoir modelling, and prediction of dynamic storage capacity, however, depends upon accurate depositional interpretations relating to an understanding of the stratigraphic architecture. Throughout most of the basin, the Precipice Sandstone is generally considered to have good reservoir properties and lateral continuity. Refined depositional models and a widely-applied sequence stratigraphic framework will enhance prediction of the most prospective play segments for CO2 injection. We utilize integrated ichnological-sedimentological facies analysis from core to interpret the Precipice Sandstone as a braided fluvial to braid-delta succession, overlain by lower delta plain to subaqueous delta and estuarine embayment deposits of the Evergreen Formation. Facies successions and core-calibrated wireline logs show brackish-water influenced deposits at several stratigraphic intervals. Brackish-water influenced deposits overlie upper delta plain or braid-plain sediments. They occur laterally adjacent to subaerial lower delta plain strata, and generally cap parasequence-sets. Seismic surveys resolve lower-order cyclicity, showing parasequence-sets within the Precipice succession that retrograde or aggrade and onlap the basal-Surat unconformity. This stratal arrangement reflects the lowstand and early transgressive systems tracts of a 2rd order depositional sequence or a distinct 3th order sequence. Late transgressive and early highstand systems tracts are more abundant within the lower Evergreen Formation and are interpreted to consist of restricted or estuarine central basin deposits; but these may also represent a 3th order sequence. Additional chronometric data is needed to differentiate between these interpretations. Depositional and sequence stratigraphic interpretations suggest the Precipice Sandstone has a higher degree of heterogeneity than previously appreciated. Moreover, we show that the Evergreen Formation is not a simple basin-wide sealing unit due to the presence of sandstone geobodies that complexly cross-cut each other (i.e., the ‘Boxvale Sandstone Member’) that may act as vertical fluid conduits. The sequence stratigraphic characteristics of the reservoir-seal pair should be carefully considered when selecting locations for CO2 sequestration.

Stratigraphic framework and petrophysical analysis of Oligocene-miocene turbidite systems in the eastern Marlim oilfield (SE Brazil)

The Eastern Marlim oilfield, located in the northeastern offshore of the Campos Basin, is a portion of the Marlim Complex, one of the most important oil accumulations ever found in Brazil. This paper presents findings from lithofacies, sequence stratigraphy and petrophysical analyses for the Oligocene-Miocene section of the Eastern Marlim oilfield. Here, we evaluate at least four main lithofacies associations and three major zones recognized in the latter section, presenting sedimentological and stratigraphical interpretations based on stratigraphic correlations, distribution and sand proportion maps, and accompanying petrophysical analysis. Our findings suggest at least two bipartite turbiditic flows representing different stages of deposition associated with a deep-water turbidite sequence, composing the elements of a submarine lobe complex. Massive unconsolidated amalgamated sandstone bodies, displaying very good porosity, lateral and vertical continuity, reflecting excellent reservoirs. The final depositional model of the studied Oligocene-Miocene interval in this work is part of the first-order Highstand System Tract (HST) of the Campos Basin, which in turn represents a second-order, exploration-scale depositional sequence. Finally, the sequence stratigraphic model of the Oligocene-Miocene section of the Eastern Marlim oilfield has an architecture similar to those that have been developed from Oligocene-Miocene global sea level changes.

Characterizing the Middle–Upper Miocene Reservoir Intervals of a Producing Field in the Niger Delta Basin: An Application of Facies, Sequence Stratigraphic and Petrophysical Analyses

Well log and core data were used to carry out detailed facies, sequence stratigraphic, and petrophysical analyses of the “Iota field” in the onshore Niger Delta Basin. The aim was to recognize facies distribution, environments of deposition, stratigraphic framework, reservoir continuity, and property distribution for better understanding of reservoir characteristics across the field. Sedimentological evidence reveals the occurrence of fifteen lithofacies, which were further classified into eight facies associations. The facies associations depict deposition in the offshore, offshore transition, lower shoreface, upper shoreface, estuarine channel, tidal channel, and fluvial channel environments. Sequence stratigraphic analysis reveals the occurrence of three maximum flooding surfaces and three sequence boundaries, which reflect series of transgressive and regressive episodes during the Serravallian–Tortonian age. Two depositional sequences comprising lowstand system tract, transgressive system tract, and highstand system tract packages were recognized. The sand and shale of the fluvial, tidal, estuarine, shoreface and offshore deposits, constitute the reservoir and seal/source rock packages. Correlation indicates that the reservoir packages have good lateral continuity, except where channel incision has occurred. Petrophysical analysis shows that the reservoir units have fair-to-good porosity and good- to-excellent net-to-gross qualities. Dominance of oil-bearing zones were detected at shallow to deeper interval at the northern section of the study area, with few gas-bearing intervals occurring at the intermediate intervals of the southern section. Overall, integrated analytical approach has provided more insight into the facies and reservoir quality distribution, thus reducing subsurface reservoir uncertainties.

Optimalisasi Proses Komputasi Pelebaran Pita Frekuensi Data Seismik Refleksi Berbasis Inversi Beresolusi Tinggi untuk Penafsiran Stratigrafi Seismik

Resolution capability of seismic reflection data is becoming more interesting topic to discuss even for today. Several methods and approximations to attempt bandwidth extension of seismic reflection data have been proposed in wide variety. Among them is a non-stationary reflectivity inversion based on basis pursuit decomposition technique. The need of the method is increasing as it can provide realistic resolution of seismic data. The main advantages of the method are consistancy with log data, good lateral continuity, preserve amplitude and capable in denying artificial reflection feature. Nevertheless, its computational process is very expensive thus most pratitioners tend to avoid the method and look for another method that could serve quicker instead of better results.This paper attempt to propose a set of computational scheme which can be used flexibly for any prospective user to reduce the computational cost of the method.

Near-surface and anisotropy modeling for efficient land seismic depth imaging in low-relief geology

Prestack depth migration of land data presents unique characteristics and challenges that distinguish it from the workflows applied for marine data. Such unique characteristics are primarily related to the near surface. In areas of low-relief geology, near-surface velocity variations can obscure the reservoir structure. The remaining deeper earth model section has good lateral continuity and can be described effectively by smooth velocity fields. Strategies for estimating the near-surface effects and incorporating them into a processing workflow are of primary importance for the successful depth imaging of land seismic data. The second important aspect of a depth imaging workflow is that the seismic image must honor the well markers or formation tops. The subhorizontal fine-scale layering of low-relief structures can cause anisotropy that needs to be taken into account to achieve accurate well ties and good image quality. We have evaluated the application of an efficient workflow to achieve fast and reliable depth imaging in layered geology; this involves the decomposition of the near-surface velocity into short-, medium-, and long-wavelength terms followed by reflection velocity analysis and anisotropic parameter scanning. The long-wavelength components are solved by dynamic velocity analysis, whereas the medium- and short-wavelength terms are evaluated by surface-consistent analysis applied to refracted and reflected data. Interaction with seismic interpreters and geology-consistent updates mitigates the possibility of introducing errors in areas not covered by wells. The workflow is applied to a structure-controlled wadi in central Saudi Arabia showing complex near-surface conditions and imaging problems. The study incorporates high-resolution helicopter-borne transient electromagnetic data that are used to constrain seismic traveltime inversion through cross-gradient structural regularization (joint inversion). Fast and robust depth imaging constrained by well data is obtained through accurate estimation of near-surface velocities, anisotropy, and geology-consistent analysis.

Stratigraphic analysis and calculation of reserves in the Colorado field, MMV, Colombia

Based on review of previous information and correlation of 7 lithostratigraphic sections from well data, it was possible to establish the presence of channels in fluvial environments of the Mugrosa Formation, with good lateral continuity, in the B and C zones, in the Middle Magdalena Valley Basin (VMM). The results of well log interpretation (NSP logs) indicate the presence of channel sands and proved the previous sedimentological model of the field. In the sedimentological model proposed, zones B and C (Mugrosa Formation) show a very good lateral continuity of sands. The reserve calculations of original oil in place (OOIP) and original gas in place (GOES) indicates that the largest reserves of oil and gas are located in the zone C, with reserves of 118 million bbl and 33.9 Gigas of cubic feet respectively.

Evolução estratigráfica da Sequência Neocarbonífera-Eotriássica da Bacia do Parnaíba, Brasil

RESUMO: A Sequência Neocarbonífera-Eotriássica corresponde ao terceiro grande ciclo sedimentar da Bacia do Parnaíba e concerne litoestratigraficamente ao Grupo Balsas. Essa sequência é descrita como um conjunto de rochas cujos sedimentos foram depositados em um ambiente complexo, clástico/evaporítico de mar raso, gradando para um ambiente lacustre/desértico. O principal objetivo deste trabalho foi realizar uma análise estratigráfica da Sequência Neocarbonífera-Eotriássica, visando uma melhor compreensão da sua evolução. Tal análise teve por base dados de poços e algumas seções sísmicas. Para o intervalo estratigráfico em questão foram identificadas três sequências deposicionais. A Sequência 1 corresponde a rochas que foram depositadas inicialmente a partir de um sistema fluvial, que passa para um sistema marinho raso implantado durante uma fase transgressiva e, posteriormente, evolui para um sistema deltaico. A Sequência 2 corresponde a rochas que foram depositadas a partir de um sistema deposicional lacustre/desértico, representando uma fase regressiva importante que culmina com a implantação de um sistema desértico, o qual corresponde à Sequência 3. Na análise sismoestratigráfica foi possível reconhecer as superfícies cronoestratigráficas e os tratos de sistemas identificadas em poços e analisar a sua expressão lateral. De modo geral, as sismofácies reconhecidas nas seções sísmicas apresentam-se com configurações paralelas a subparalelas, com grande continuidade lateral, sugerindo uma homogeneidade nas taxas de sedimentação durante a deposição dessas sequências, nesse setor da bacia.

Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)

Abstract Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelf.

Carbonate Deposition In Restricted Basins: A Pliocene Case Study From the Central Mediterranean (Northwestern Apennines), Italy

Abstract Carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness, because of their significance in petroleum geology. However, spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic-dominated or mixed carbonate–siliciclastic systems. Pliocene successions of Tuscany and the Tyrrhenian shelf (Northern Apennines, Italy) record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation. This study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves. Analyses of the extension, composition, facies, and sequence stratigraphic architecture of the studied Piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data, which document the slightly diachronous development of the carbonates within Mediterranean planktonic foraminifera Subzones MPL4b and MPL5a and magnetic polarity Chron C2An. The carbonate units are part of a regionally defined, tectonically controlled sequence, and represent the first transgressive unit overlying the basal sequence boundary, but are also found in the regressive portion of the sequence. Collectively, the units document the establishment of a shallow-marine carbonate factory, dominated by calcareous red algae, the larger benthic foraminifer Amphistegina, and heterozoan skeletal components, along the margins of a complex, archipelago-like coastal domain. A review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by: a) spatial discontinuity; b) an overall skeletal association consistent across separate basins, but with local variability in dominant skeletal components; c) preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems; d) predominance of low- to moderate-energy facies; e) preferential onset of deposition during transgression, with possible development of mixed carbonate–siliciclastic facies; and f) differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins. These observations built upon the study of mid-Piacenzian carbonate units from the central Mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis.

Geological setting and characterization of a methane hydrate reservoir distributed at the first offshore production test site on the Daini-Atsumi Knoll in the eastern Nankai Trough, Japan

To obtain basic information for methane hydrate (MH) reservoir characterization at the first offshore production test site (AT1) located on the northwestern slope of the Daini-Atsumi Knoll in the eastern Nankai Trough, extensive geophysical logging and pressure coring using a hybrid pressure coring system were conducted in 2012 at a monitoring well (AT1-MC) and a coring well (AT1-C). The MH-concentrated zone (MHCZ), which was confirmed by geophysical logging at AT1-MC, has a 60-m-thick turbidite assemblage with sublayers ranging from a few tens to hundreds of centimeters thickness. The turbidite assemblage is composed of lobe/sheet-type sequences in the upper part and relatively thick channel-sand sequences in the lower part. Well-to-well correlations of sandy layers between two monitoring wells within 40 m of one another exhibited fairly good lateral continuity of sand layers in the upper part of the reservoir. This suggests an ideal reservoir for the production test.The validity of MH pore saturation (Sh) evaluated from geophysical logging data were confirmed by comparing with those evaluated by pressure core analysis. In the upper part of the MHCZ, Sh values estimated from resistivity logs showed distinct differences between the sand and mud layers, compared with Sh values from nuclear magnetic resonance (NMR) logs. Resistivity logs have higher vertical resolution than NMR logs; therefore, they are favorable for these types of thin-bed evaluations. In the upper part, Sh values of 50%–80% were observed in sandy layers, which is in fairly good agreement with core-derived Sh values. In the lower part of the MHCZ, Sh values estimated from both resistivity and NMR logs showed higher background values and relatively smoother curves than those for the upper part. In the lower part, Sh values of 50%–80% were also observed in sandy layers, and they showed good agreement with the core-derived Sh values.

Quantifying the transferability of hydraulic parameters using geostatistics: The Boom Clay Case

The Boom Clay is currently investigated as potential host formation for the deep disposal of high-level and/or long-lived radioactive waste in Belgium. As such, the formation is expected to play a role of natural barrier, to slow the migration of radionuclides towards the biosphere for a sufficiently long time when the man-made barriers are no longer effective. In this context, the Boom Clay aquitard requires to be precisely characterized in terms of hydrogeological parameters, to confirm its role of geological barrier between its surrounding aquifers. Therefore, hydraulic conductivity and migration parameters have been intensively measured over the years in a few boreholes in Belgium; the latter are mainly located in the Mol-Dessel area, assuming historically a good lateral continuity of the geology. Combining these measurements with more densely acquired geophysical information allows quantifying their spatial variability and consolidating the continuity assumption. From a methodological point of view, the modeling of hydrogeological parameters requires to solve several issues. First, it is required to find a consistent geo-reference coordinate system allowing to laterally correlate thin observations derived from boreholes separated by several tens of kilometers. Then, in order to provide a reliable 3D model, it is compulsory to integrate the correlation between the scarcely sampled target parameters (core measurements) and numerous geophysical logs (gamma ray, resistivity). Geostatistics provides a suitable framework to analyze and solve these issues. Finally, a 3D model of the target parameters is proposed, together with an uncertainty envelope. This uncertainty quantification is of significant added value to assess the efficiency of the geological barrier. Besides the actual modeling of target parameters, the paper also presents sampling recommendations for forthcoming boreholes.