3D Seismic Data Research Articles

On the applicability of seismic attributes in the description and interpretation of mass-transport deposits

Mass transport deposits (MTDs) have gained economic importance in the last years because of their significance as seals or stratigraphic trapping mechanisms in deep water turbidite prospects. The analysis of MTDs in 3D seismic data provides a better understanding of their characteristics when compared to outcrop or 2D seismic data, as it is possible to capture both internal and external features over large areas in 3D. Moreover, this analysis can be further improved by applying seismic attributes, which have been employed only to describe specific aspects of these deposits. In this study, we applied several seismic attributes systematically in the characterization of an MTD, located in the northern Santos Basin (offshore southeastern Brazil), aiming to identify their applicability in the description and interpretation of 33 characteristics of this kind of deposit. As a result, it was possible to identify which features of the MTD the application of seismic attributes is indispensable, helpful, or redundant.

Fault Identification of U-Net Based on Enhanced Feature Fusion and Attention Mechanism

Accurate fault identification is essential for geological interpretation and reservoir exploitation. However, the unclear and noisy composition of seismic data makes it difficult to identify the complete fault structure using conventional methods. Thus, we have developed an attentional U-shaped network (EAResU-net) based on enhanced feature fusion for automated end-to-end fault interpretation of 3D seismic data. EAResU-net uses an enhanced feature fusion mechanism to reduce the semantic gap between the encoder and decoder and improve the representation of fault features in combination with residual structures. In addition, EAResU-net introduces an attention mechanism, which effectively suppresses seismic data noise and improves model accuracy. The experimental results on synthetic and field data demonstrate that, compared with traditional deep learning methods for fault detection, our EAResU-net can achieve more accurate and continuous fault recognition results.

Growth and transtensional reactivation of a basin-bounding fault: Chengbei Sag, Bohai Bay Basin, East China

Models of extensional fault systems are predominantly based on examples where extension is approximately orthogonal to rift boundaries and deformation can be regarded as plane strain. In contrast, extensional faults in transtensional or strike-slip settings present complex geometric and kinematic features due to rotational deformation, and distinct rift and post-rift phases may be difficult to separate. Well-constrained 3D seismic data from the Bohai Bay Basin, East China reveal the growth history and transtensional reactivation of a basin-bounding fault (Chengbei Fault). During the syn-rift phase, the Chengbei Fault reached its near-final length within ∼24 Ma via the propagation and linkage of six initial fault segments, accompanied by the accumulation of 26% of its total displacement; in the following ∼18.7 Ma of the Paleogene, it accumulated the remaining 74% of displacement without an obvious increase in fault length. Following a phase of relative quiescence in the early Neogene, the Chengbei Fault was reactivated at ∼12 Ma, associated with the enhanced activity of a continental-scale strike-slip fault. At least 17 fault segments developed quickly and linked vertically to the lower fault system of the Chengbei Fault. The plan-view en-echelon and horse-tail configuration, and the flower structure seen in section views of the fault system, indicate that the post-rift activity of Chengbei Fault has had both dip-slip and strike-slip components. A calculation of the rotational deformation using fault heaves and orientations indicates that the tectonic reactivation occurred in a strike-slip-dominated transtensional setting accompanied by an increasing extension component with time. In basins affected by strike slip, kinematic analyses that consider rotational deformation can provide more detailed and convincing information on the tectonic setting.

Seismic characteristics and AVO response for non-uniform Miocene reservoirs in offshore eastern Mediterranean region, Egypt

The Eastern Mediterranean region, extending from the Offshore Nile Delta Cone of Egypt to the Levant Basin, is a confirmed hydrocarbon-rich territory with several giant gas discoveries. Numerous gas fields have been discovered in the Miocene reservoirs within the Nile Delta Cone, and the Levant Basin. The Miocene sedimentary sequences in this region are extremely heterogeneous, consisting mainly of turbiditic slope deposits, channels, and basin floor fans that were capped by evaporites formed during the Messinian Salinity Crisis. As a result, the seismic characteristics and interpreted properties of this heterogeneous section are ambiguous. The study area is located in the Offshore North Sinai Basin, where a thick Early Miocene section was deposited midway between the Nile Delta province, which includes the El-Fayrouz discovery, and the Levant Basin, which includes Tamar, Tanin, and several other discoveries. This study uses quantitative seismic interpretations methods, such as amplitude variations with offset and fluid replacement modeling, to assess the seismic acoustic impedance trend with depth. Also, determine the seismic amplitude response for the brine and gas sands reservoir of the Early and Late Miocene section to link the unexplored study area within the North Sinai Offshore Basin with the explored Nile Delta and Levant Basins. In addition to evaluate direct hydrocarbon indicator (DHI) of the dimming seismic amplitude that is compatible with the structure’s last closed contour of the Syrian Arc anticline of the Early Miocene reservoirs (EMT-1 prospect). Different vintages of 2D and 3D seismic data, six wells, and various published data were used in this study. The quantitative interpretation shows the pitfalls of the acoustic impedance trend and seismic response dependency on depth for gas and brine sand, which led to the drilling of the EMT-1 dry well. Also, the fluid replacement, P-wave velocity (Vp), and density (ρ) modeling confirmed that the seismic dimming amplitude was due to a seismic processing artifact, which was corrected by readjusting the overburden Messinian salt processing velocity model. This research concludes that the seismic quantitative interpretations are successfully used to assess the acoustic impedance versus depth and understand DHI pitfalls, as well as the processing workflow that could enhance the seismic image.

The Paleozoic Hydrocarbon System in the Gotland Basin (Central Baltic Sea) Leaks

AbstractThe Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking.

Prediction of Favourable Hydrocarbon Transport Pathways of the Jiuzhou Fault in Langgu Sag, Bohai Bay Basin

The Jiuzhou fault in the Langgu Sag of the Bohai Bay Basin is a significant oil-source fault that connects source rocks and reservoirs, and thus it can transport oil and gas during the hydrocarbon accumulation period. The hydrocarbon distribution characteristics along the strike of the Jiuzhou fault differ distinctly, indicating that the transport capacity in different fault segments is also different. In this study, we focused on analyzing the fault development characteristics to accurately predict the location of favorable hydrocarbon transport pathways on the Jiuzhou fault. We found that the zones superimposed by paleo relay ramps developed before hydrocarbon accumulation, active faulting areas during hydrocarbon accumulation, and transport ridges of the fault are favourable along-fault locations for transporting hydrocarbons. Based on this idea and 3D seismic data, we investigated the distribution of the paleo relay ramps of the Jiuzhou fault and the fault activity rate during hydrocarbon accumulation using the maximum throw subtraction method. Then, the burial depth contour was employed to search hydrocarbon transport ridges of the fault and therefore predict the location of favourable hydrocarbon transport pathways of the Jiuzhou fault. The prediction results show that there are totally 4 favorable hydrocarbon transport pathways, where hydrocarbons are more likely to migrate vertically and finally accumulate in the overlying formations. In addition, the pathway locations of the Jiuzhou fault are consistent with the hydrocarbon distribution in the study area, demonstrating that this method is reliable and feasible for predicting the favorable hydrocarbon transport pathways of oil-source faults.

Sedimentary deformation relating to episodic seepage in the last 1.2 million years: a multi-scale seismic study from the Vestnesa Ridge, eastern Fram Strait

Seafloor hydrocarbon seepage is a natural fluid release process that occurs worldwide on continental shelves, slopes, and in deep oceanic basins. The Vestnesa sedimentary ridge in the eastern Fram Strait hosts a deep-water gas hydrate system that became charged with hydrocarbons ∼2.7 Ma and has experienced episodic seepage along the entire ridge until a few thousand years ago, when seepage activity apparently ceased in the west but persisted in the east. Although it has been documented that faults and fractures play a key role in feeding the seeps with thermogenic gases, the mechanisms controlling seepage periodicity remain poorly understood. Here we integrate high-resolution P-cable 3D seismic and Chirp data to investigate the spatial and temporal evolution of high-resolution fractures and fluid flow features in the west of the Vestnesa Ridge. We characterize sediment deformation using a fracture density seismic attribute workflow revealing two highly deformed stratigraphic intervals and associated small-scale pockmarks (<20 m diameter). Chronostratigraphic constraints from the region show that these two highly deformed intervals are influenced by at least three major climatic and oceanic events during the last 1.2 million years: the Mid-Pleistocene Transition (∼1.25–0.7 Ma), the penultimate deglaciation (∼130 ka) and the last deglaciation (Heinrich Stadial 1: ∼16 ka). These periods of deformation appear associated with seismic anomalies potentially correlated with buried methane-derived authigenic carbonate and have been sensitive to shifts in the boundary of the free gas-gas hydrate interface. Our results show shifts (up to ∼30 m) in the depth of the base of the gas hydrate stability zone (GHSZ) associated with major changes in ocean bottom water temperatures. This ocean-driven effect on the base of the GHSZ since the Last Glacial Maximum coincides with the already highly deformed Mid-Pleistocene Transition sedimentary interval and likely enhanced deformation and gas leakage along the ridge. Our results have implications for understanding how glacial cycles impact fracture formation and associated seepage activity.

The delta-fluvial evolution of a lacustrine basin with gentle slope and low sedimentation rate: A case study of the Fudong Slope, Junggar Basin, Northwest China

Gentle slope belts of lacustrine basins are important areas for the generation of stratigraphic petroleum reservoirs controlled by sedimentary systems. Based on coring, well logging, 3D seismic and analytical test data, the sedimentary system and sandbody distribution characteristics of the Jurassic Toutunhe Formation (J2t) in the Fudong slope of the Junggar Basin were analysed. The results indicated that the Fudong slope showed the characteristics of low sediment input. Sediments mainly originated from the Shaqi uplift, and the sediment input gradually weakened from the early to the late J2t stages. The sedimentary system evolved from a delta to a meandering river, resulting in a delta front facies in the 1st member (J2t1) and a meandering river facies in the 2nd (J2t2) and 3rd (J2t3) members of the Toutunhe Formation. A sedimentary evolution pattern for the gentle slope with low sediment input was established. Thick deltaic sandbodies developed locally in the J2t1 stage. However, meandering rivers with high sinuosities predominantly developed and resulted in a striped geometry in the J2t2 and J2t3 members. Moreover, the meandering sandbodies exhibited an anastomosing morphology after multistage superposition. The channel and point bar facies in J2t2 were more developed than those in J2t3 because of sediment input differences. Under low-sediment input conditions, the sedimentary environment of the gentle slope belt in the lacustrine basin was controlled by changes in the palaeoclimate, palaeogeomorphology, gradient (slope) and base level. Palaeoclimate was the main factor controlling the evolution of the sedimentary environment. Palaeogeomorphology and slope controlled the distribution of sedimentary microfacies, channel sinuosity and sandbodies. Base-level change restricted the sandbody superimposition style. Under the low sediment input conditions of the Fudong slope, the subaqueous distributary channels of the delta environment and the point bars of the meandering river environment in the transitional belt of the Fudong slope are the main potential targets for stratigraphic petroleum reservoirs, whilst the 2nd member of the Toutunhe Formation (J2t2) is the main favourable interval for stratigraphic reservoir exploration.

SPATIOTEMPORAL DISTRIBUTION OF THE CONGLOMERATE RESERVOIR JATIBARANG FORMATION, MELANDONG FIELD, NORTH-WEST JAVA BASIN, INDONESIA

Subsurface mapping of the distribution of the reservoir is essential to be conducted in order to minimize many risks such as financial losses and also to increase profit from hydrocarbon production. This research was conducted on the Jatibarang conglomerate reservoir in Melandong Field, North West Java Basin, Indonesia. There are three objectives of this study which are to perform elastic impedance (EI) seismic inversion using available 3D seismic data, to determine the most suitable elastic impedance angle for the data, and to map spatiotemporal distribution of the Jatibarang Formation reservoir in the Melandong field, North West Java basin, Indonesia. EI inversion was selected for this study using the inversion angle ranging from the near stack (5º-15º) to the far stack (20º-30º). Results from this study show that EI seismic inversion can help in detecting the distribution of the lithology and hydrocarbon within the target zone. Angle 5º is considered as the best EI angle for the studied data as indicated by a correlation value of 0.65. Moreover, EI angles 15º and 10º are less reliable as shown by their correlation value of 0.6 and 0.56, respectively. These results are expected to provide some new insights into the distribution of the Jatibarang reservoir, and help in exploration, exploitation, and development of oil and gas fields in Melandong Field, North West Java Basin, Indonesia.

Innovative 3D modeling of an old oil field for sustainable production: Case study of Katin-Barbes oil field (KBOF), SE Anatolia- Turkey

The goal of this study is to establish a workflow for the re-interpretation of almost depleted fields targeting the long-term sustainable oil production; in particular, for the oil fields in Turkey and the neighboring Middle Eastern countries located on the fold and thrust belts of the Zagros Mountains. It also fills some of the gaps in our understanding of the northern part of the Arabian Platform by describing the seismic characteristics of the Cretaceous reservoirs that were deposited during the Aptian to Turonian. The Katin-Barbes oil field (KBOF) in SE-Turkey was used as a case study. In this area, 3D seismic data were used for structural interpretation and re-modeling of Cretaceous carbonates sedimented in the complex tectonic region. The well logs from 55 wells in the field were used to create a compilation of formation tops and were used as reference points for two separate sets of 3-D seismic data, acquired in 1991 and 2017. The quality of seismic data was improved with interpretation filters. The structural model was obtained by using various qualifiers from the seismic cubes and seismic facies changes were identified by analyzing a number of seismic attributes. Therefore, seismic data and velocities from the borehole measurements were combined to form a velocity model in building a structural model. Seismic attributes and well logs were used to create a porosity model. Consequently, top and base of two reservoir units; the Derdere and Sabunsuyu Formations have been clarified and re-defined, and potential new well locations were identified. Depending on the results of this investigation, 9 new wells were drilled in the potential areas in the KBOF, recently. Except the last one drilled on the NE boundary of the northern block, all wells have been completed as the “oil producing wells” and top of the reservoir units were encountered at almost the same depths in our depth model. Therefore, results and proposed methods in this research are confirmed by the real, borehole data. This research will be an examplary study for the re-evaluation of older and/or almost depleted oil fields, either in Turkey or in the other Middle Eastern countries.

3D reflection seismic imaging of natural gas/fluid escape features in the deep-water Orange Basin of South Africa

Many features indicative of natural gas and oil leakage are delineated in the deep-water Orange Basin offshore South Africa using 3D reflection seismic data. These features are influenced by the translational and compressional domains of an underlying Upper Cretaceous deep-water fold-and-thrust belt (DWFTB) system detaching Turonian shales. The origin of hydrocarbons is postulated to be from both: (a) thermogenic sources stemming from the speculative Turonian and proven Aptian source rocks at depth; and (b) biogenic sources from organic-rich sediments in the Cenozoic attributed to the Benguela Current upwelling system. The late Campanian surface has a dense population of > 950 pockmarks classified into three groups based on their variable shapes and diameter: giant (> 1500 m), crater (~ 700–900 m) and simple (< 500 m) pockmarks. A total of 85 simple pockmarks are observed on the present-day seafloor in the same area as those imaged on the late Campanian surface found together with mass wasting. A major slump scar in the north surrounds a ~ 4200 m long, tectonically controlled mud volcano. The vent of the elongated mud volcano is near-vertical and situated along the axis of a large anticline marking the intersection of the translational and compressional domains. Along the same fold further south, the greatest accumulation of hydrocarbons is indicated by a positive high amplitude anomaly (PHAA) within a late Campanian anticline. Vast economical hydrocarbon reservoirs have yet to be exploited from the deep-water Orange Basin, as evidenced by the widespread occurrence of natural gas/fluid escape features imaged in this study.

Cenozoic evolution and deformation in the Eastern and Western Depression of the Liaohe Subbasin, Bohai Bay Basin: Insights from seismic data

AbstractIn rift basins with multiphase extension, the reactivation of pre‐existing faults plays an important role in the evolution and partitioning of deformation. The Liaohe Subbasin is located in the northeastern Bohai Bay Basin, and the Tanlu Fault Zone (TLFZ) runs through it and experienced extension and right‐lateral strike‐slip during the Cenozoic. Therefore, it is an ideal region for studying the deformation and evolution of rift basins. Based on 3D seismic data, we document the structure and fault characteristics of the Eastern and Western Depressions of the Liaohe Subbasin, identify periods of activity on normal and strike‐slip faults, and analyse the evolution and mechanisms of the Cenozoic evolution of this subbasin. Our main results show that (1) the main faults in the Western Depression exhibited extensional motion throughout the Palaeocene, while the Eastern Depression exhibited significant right‐lateral motion during the Oligocene following the early extension stage. (2) The Cenozoic evolution of the Liaohe Subbasin can be divided into four stages: (i) an initial extension stage (the Palaeocene to the Eocene), (ii) an extension stage with initial strike‐slip (Early Oligocene), (iii) a right‐lateral strike‐slip stage (Late Oligocene) and (iv) a postrift stage (after the Neogene). (3) The upwelling of mantle material caused by the subduction and rollback of the Pacific Plate led to the extension of the Liaohe Subbasin from the Palaeocene to the Eocene. The TLFZ began right‐lateral motion at 40 Ma and experienced strong right‐lateral deformation when rifting was weak in the Oligocene and enhanced deformation after 12 Ma. (4) In this multiphase rifting process, under moderate obliquity, strike‐slip deformation is obvious in the areas close to pre‐existing faults, while extensional deformation is obvious in areas farther away. (5) Cenozoic extension and strike‐slip deformation due to partitioning of strain are caused by obliquely reactivation of TLFZ. This study suggests that the reactivation of pre‐existing strike‐slip faults plays a major role in evolution and strain partitioning. Moreover, the results will contribute to future hydrocarbon exploration in multiphase rift basins.

Delineation of oil–water contact within Tipam reservoir: A study from Upper Assam Basin, North‐East India

Fluid contacts within a reservoir can vary either because of compartmentalization by faults, lithological variations, hydrocarbon fill history or changes in the hydrodynamic activity of fluids. Their detailed interpretation is significant for estimating potential reserves and developing an explored hydrocarbon field. This study uses high‐quality three‐dimensional (3D) seismic reflection data to decipher the fluid contact zones and their types from the well‐known Tipam reservoir in the petroliferous Upper Assam foreland basin. Different seismic attributes are used to understand the seismic response of fluids and associated structures that structurally control the reservoir geometry. Fluid contact analysis is performed by amalgamating these responses within the target interval. The analysis indicates that the south‐west part of the reservoir is a promising hydrocarbon‐bearing zone and consists of oil–water contacts. These contacts possess a dominant trend of NE–SW within the reservoir. Further, a decreasing trend in the density, velocity and an increasing trend in the resistivity and porosity logs of the wellbore SC‐2 calibrates these inferences and confirms the presence of oil‐bearing zones underlain by water in the SW part of the Tipam reservoir. Thus, the Upper Assam foreland basin is a promising area for hydrocarbon exploration, in which Mid‐Miocene sequences are the potential leads that can be unlocked. The analysis presented through this research could be efficiently and similarly carried out in onshore basins worldwide.

Data Assimilation of Production and Multiple 4D Seismic Acquisitions in a Deepwater Field Using Ensemble Smoother with Multiple Data Assimilation

Summary In recent years, time-lapse (4D) seismic (4DS) data have been widely used for reservoir monitoring to provide relevant information on dynamic changes occurring during production. In complex reservoirs, multiple seismic monitor surveys are usually available. Updating reservoir models with these data can be very beneficial to improve the field’s management. In the quantitative integration of 4DS data into the data assimilation (DA) process, it is crucial to define how to deal with more than one seismic monitor. In this work, we continue a series of investigations about seismic DA procedures and expand on them by analyzing ways to assimilate more than one seismic monitor. More specifically, we evaluate different ways of using production data and two monitor surveys (M3 and M5) to calibrate the dynamic models of a real Brazilian reservoir using the ensemble smoother with multiple data assimilation (ES-MDA) method. We performed the following experiments: (1) sequential assimilation of M3 and M5 with parts of well history divided according to the seismic acquisition dates; (2) assimilation of M3 with the entire well history and subsequent assimilation of M5; (3) assimilation of well and M3 data; and (4) assimilation of well and M5 data. For comparison purposes, we also assimilated only well data. From the results, we observed that well and 4DS data misfits were reduced when assimilating both monitors, compared to the cases where only a single monitor (any of them) was used with production data. This conclusion is also true in the comparison with results obtained when only assimilating well data. This indicates that both seismic monitors are important data to be quantitatively considered in DA. In this particular field, using a previous DA run to solely assimilate the newly available monitor (Case 2) delivered better models and long-term forecasts. Therefore, this would be our recommendation. This study highlights the importance of several 4DS acquisitions for reservoir monitoring and management and shows the challenges of their application in seismic DA for better life cycle field applications.

Seismic forward modeling for investigating and interpreting thin beds in a carbonate reservoir in SW Iran

High-frequency contents of reflections are essential in the investigation and interpretation of thin-bed reservoirs. These beds can be even more complicated in carbonate rocks, as pore geometries influence final seismic responses. To address these complexities, we propose a seismic forward modeling workflow to investigate several thin-bed reservoirs in a carbonate oilfield with variable pore geometries. The new workflow enhances the existing forward models for the investigation of thin beds by integrating seismic petrophysics, geological model building, and 2D finite-difference elastic modeling. We used seismic petrophysics to ensure the consistency between petrophysical well logs and seismic data using rock physics modeling. Then, we introduced a new high-resolution workflow for velocity modeling to build a reliable geological model. Finally, the 2D finite-difference elastic modeling is employed to generate synthetic traces based on our geological model to obtain seismic responses for the existing thin-bed reservoirs. The forward models used in this study are a powerful tool for investigating thin layers because they enable high-resolution investigation of the given geological model in distinguishing lateral and vertical lithofacies changes. The new velocity modeling workflow, implemented in this research, is more reliable and effective than the conventional velocity property modeling approaches, which resulted in synthetic seismic sections with increased lateral and vertical resolutions and enhanced data from a thin bed. The main features of this workflow are the incorporation of well-log data into geological model building, combining the high-resolution data of horizontal seismic stacking velocity with vertical well logging, and the incorporation of a residual model to improve the seismic stacking velocity. We produced a more coherent section resembling the acquired 3D seismic data by applying the proposed workflow to data from an oil carbonate reservoir in the Fahliyan Formation within the Abadan Plain in SW Iran. It is concluded that the higher frequency synthetic sections from the proposed workflow can assist in resolving the seismic interpretation challenges. By applying the proposed workflow to the current data set, four thin-bed carbonate reservoirs were investigated with corresponding thicknesses of approximately 25, and 17 m at peak frequencies of 60, and 90 Hz, respectively.

Determination of effective seismic wave velocities using time gradients obtained from response and CDP reflection hodographs

Seismic wave velocities, including effective velocities, play a critical role in the kinematic processing and interpretation of 2D and 3D seismic data. Along with other parameters of elastic waves, the geological efficiency of seismic exploration also depends on the level of knowledge of the velocity model of the medium, on the accuracy of information about velocities. The article briefly lists the main methods for determining the effective velocities according to the seismic wave field, developed and applied in the practice of seismic research. The methods used to determine the effective velocities of reflected waves can be divided into two groups: methods for determining the effective velocities based on automatic or visual tracking of the in-phase axes (i.e. hodographs) of reflected waves on seismic records, then their approximation by hyperbolas constitute the first group, and the second the group consists of methods based on the application of the analysis of the seismic wave field in controlled directions on the seismograms of a common depth point (CDP). Each proposed method for determining effective speeds has advantages and disadvantages. The article focuses on the industrial method, widely used at present, based on the analysis of the wave field in controlled directions, which do not provide sufficient information to solve the main problems of kinematic interpretation. The main disadvantages of the existing methods are indicated. The article describes a new method for determining the effective velocity, which is fundamentally different from the methods that are still used in the practice of seismic exploration. The fact is that in this method, seismic survey data of single and multiple profiling are not used separately, as it was in the methods used in seismic survey practice so far, but together. Formulas have been derived for determining the effective velocity based on the time gradients of the travel time curves of the CSP and CDP of reflected waves, which makes it possible to determine the speeds even from incomplete travel time curves. A technique for determining the effective speed has been developed and a sequence of procedures has been determined for solving the problem. The results of research are given on a specific example by solving the direct and inverse problems for the Sazhdag area between the Kura and Gabyrra rivers. The influence of errors in the values of the parameters included in the formula for calculating the effective speed on the final results is studied. At the end of the article, the main advantages of the proposed method are indicated.

Simultaneous off-the-grid regularization and reconstruction for 3D seismic data by a new combined sampling operator

Seismic samples are generally designed to be placed on perfect Cartesian coordinates, that is, on-the-grid. However, sampling geometry is disturbed by obstacles in field applications. Large obstacles result in missing samples. For small obstacles, geophones or sources are placed at an available off-the-grid location nearest to the designed grid. To achieve simultaneous off-the-grid regularization and missing data reconstruction for 3D seismic data, we develop a new mathematical model based on a new combined sampling operator, a 3D curvelet transform, and a fast projection onto convex sets (FPOCS) algorithm. The sampling operator is combined with a binary mask for on-the-grid samples reconstruction and a barycentric Lagrangian (BL) operator for off-the-grid samples regularization. A 2D BL operator is obtained using the tensor product of two 1D BL operators. The inversion problem is efficiently solved based on FPOCS. This method is tested on synthetic and field data sets. The reconstruction results outperform the methods based on the binary mask in terms of signal-to-noise ratio and visual effect.

Crossline Reconstruction of 3D Seismic Data Using 3D cWGAN: A Comparative Study on Sleipner Seismic Survey Data

In seismic data acquisition, data loss can occur, particularly with the use of streamer systems in marine seismic exploration. These systems often cause spatial aliasing problems by having close inline intervals and wide crossline intervals to maximize the exploration range. To improve the resolution of seismic data in the crossline direction, various machine learning techniques have been employed for crossline data reconstruction. In this study, we introduce a 3D cWGAN (conditional Wasserstein generative adversarial network) for interpolating 3D seismic data. We evaluate the model’s performance by comparing it with 2D cWGAN and 3D U-Net. In this study, two interpolation strategies are employed to reconstruct missing data in the crossline direction. The first strategy uses a 2D network, which trains a model using inline data and applies the trained model to the crossline direction via 2D cWGAN. The second strategy employs a 3D network, which uses the 3D volume of the seismic data directly via 3D cWGAN and 3D U-Net. We demonstrate the effectiveness of the proposed method using the Sleipner CO2 4D seismic survey dataset. Our results show that the 3D cWGAN is more efficient in enhancing resolution and computation compared to the 2D cWGAN or 3D U-Net.

Petrophysical properties of igneous rocks in continental rift basins – a case study from the Mesozoic sequence of the Browse Basin, North West Shelf of Australia

Capturing the ubiquitous distribution and properties of igneous rocks is necessary to succeed in hydrocarbon exploration, field development and underground gas storage when dealing with magma-rich rift margins. In recent years, numerous researches have revealed detailed morphologies of intrusive and extrusive rock units embedded within sedimentary basins owing to advances in 3D seismic data. Outcrop studies have also provided deeper understandings of their occurrence and geometries. However, there has been comparatively little focus on the rock physics of igneous bodies and their relationships to seismic expression. To bridge this gap between the outcrop and the seismic information, we undertook a well-log-based petrophysical study of igneous rocks using subsurface dataset from the Browse Basin located in the Australian North West Shelf. In this contribution, we describe a classification of volcanic facies (e.g. lava flows, volcaniclastics, intrusive sills) based on well log motifs and textures apparent in borehole image data. Statistics of the petrophysical properties of each volcanic facies are also analysed in order to examine their correlation to seismic patterns. Our study implies the importance of detailed characterisation of igneous petrophysical properties of igneous rock units where concentrated within a sedimentary basin, which will help reconcile interpretations of seismic data.

Timanian Fold-and-Thrust Belt and Caledonian Overprint in the Selis Ridge Imaged by New 3D Seismic Attributes and Spectral Decomposition

The present study is a detailed structural analysis of 3D seismic data in the Selis Ridge in the western Loppa High in the Norwegian Barents Sea, to which new seismic attributes and spectral decomposition were applied. The analysis reveals that pre-Devonian basement rocks are crosscut by a 40–50 kilometers wide, several kilometers thick, E–W- to WNW–ESE-striking fold-and-thrust belt, including a steep, kilometer-thick, top-SSW shear zone. The folds display dome- and trough-shaped geometries, the thrusts appear to have been reactivated dominantly as top-west structures, and the main shear zone warps over the top of the Selis Ridge. The fold-and-thrust belt is interpreted as part of the latest Neoproterozoic (ca. 650–550 Ma) Timanian Orogeny, which potentially reworked preexisting Neoproterozoic rift basins and highs, and was reworked during E–W Caledonian contraction in the Ordovician–Silurian. The results are analogous to recent findings in the northern Norwegian Barents Sea and Svalbard. The presented interpretation provides the basis for discussing Neoproterozoic–Paleozoic plate tectonics reconstructions, the influence of Precambrian–early Paleozoic structures on post-Caledonian fault complexes, the location of the Timanian and Caledonian suture zones, Neoproterozoic rifting, and the origin of the Seiland Igneous Province.