Stratigraphic evolution of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform Region, Malaysia

Seismic attribute analysis of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform region, Malaysia

Mass transport deposits (MTDs) have attracted widespread attention from scholars because of their powerful sediment transport ability and capping effect on shallow natural gas reservoirs. Due to the rich types and development of MTDs, the Qiongdongnan Basin (QDNB) is considered an excellent place to study the triggering mechanisms of MTDs. Based on 2D seismic data, the types, characteristics, distribution, and sources of the Quaternary MTDs in the QDNB are recorded. In addition, the triggering mechanisms and sedimentary evolutionary patterns are examined. There are three types of MTDs in the study area: shelf-attached MTDs, slope-attached MTDs, and magmatic intrusion-triggered MTDs. The shelf-attached MTDs developed in the northwestern slope of the basin, and they are thick and wide in scale. The slope-attached MTDs developed in the northeastern slope area of the basin, and they are thin and wide in scale. A magmatic intrusion-triggered MTDs are developed in the bulge area of the southern basin, with small in scale and large thickness differences. The transport direction of these MTDs is mainly from the northwest-southeast and southeast-northwest. The analysis of the tectonic-sedimentary evolution of the QDNB reveals that the MTDs may have been controlled by the following five factors: first, the bottom configuration controlled the MTDs’ flow direction; second, the amplitude of the sea-level fluctuation and the reactivation intensity of the main fault in the basin may have triggered the large-scale, attached MTDs in the northern slope area; third, the high sedimentation rate controlled the attached MTDs, the shelf-attached MTDs developed when the source supply was strong, but the slope-attached MTDs developed when the source supply was weak. Furthermore, magmatic activity controlled the development and distribution scale of magmatic intrusion-triggered MTDs in the southern QDNB.

Genesis and evolution of the mass transport deposits in the middle segment of the Pearl River canyon, South China Sea: Insights from 3D seismic data

Reconstruction of repeated Quaternary slope failures in the northern South China Sea

A 3D seismic and AUV data integration has been performed for geohazard assessment at an early stage of a field development. The study area is located on the South China Sea, approximately 100 km northwest of the coast of Brunei Darussalam margin characterized by a delta toe fold-thrust belt. Elongated mini-basins are separated by shale-cored ridges created by basin-directed thrusting. The continental slope is characterized steep slopes and affected by large channels, and mass transport deposits (MTD). A regional geohazard assessment was performed on the 3D exploration seismic data highlighting the presence of numerous seabed an sub-seabed features potentially affecting E&P activity. In order to better assess the possible impact of these geohazards on the field development, a detailed AUV survey has been performed on target areas. The study area ranges from 830 m to 2050 m of water depth and is characterized by seabed gradient up to 45°. Several events of buried MTD including more cohesive blocks which result in the hummocky signature on the present-day seabed are observed. The presence of such MTDs may induce vertical and lateral soil variability that may impact both drilling operations or pile/anchor installation and flowlines installation passing through the hummocky seabed. In addition, the slopes are affected by recent instability processes covering 2 km2 to 10 km2. Larger slide scarps with an amphitheatre-like source area are observed and appear to be created by various retrogressive events. The slides initiate on various slope angles, from 2° to 16°, and measured run-out distances show a large range of values, from hundreds to thousands of metres. Evidences of seafloor expulsion features (craters, pockmarks), shallow gas, gas hydrates are also observed within the study area. The 3D seismic dataset has been used to identify at a regional scale particular geohazards areas requiring a more detailed investigation via AUV at an engineering scale. Such engineering scale allows producing favorability maps created from selection criteria and allowing mitigation strategies for safe E&P activities.

The accretionary wedge in the incipient arc‐continent collisional zone offshore southwestern Taiwan is rich in gas hydrates as inferred from reflection seismic data and the geochemical analyses of shallow sediments. In this study, 2D and 3D seismic data were used to investigate the role of structural factors including mud diapirism on the formation of gas hydrates and associated free gas in the Quaternary Lower Fangliao Basin, a semi‐enclosed slope basin situated on the upper accretionary wedge. Albeit limited drilling information on lithostratigraphy and petroleum potential in the area together with seismic reflection data show that mud diapirs have influenced the formation of bottom‐simulating reflectors (BSRs) and the distribution of gas hydrates and free gas. On reflection seismic profiles, five seismic facies were observed and are characterised by: stratified parallel reflections; contorted reflections; semi‐parallel, high‐amplitude reflections; oblique, continuous high‐amplitude reflections; and generally transparent reflections. These seismic facies were respectively interpreted as hemipelagic sediments, mass transport deposits (MTDs), sandstone‐rich turbidites, overbank deposits and mud diapirs. The gas hydrate stability zone (GHSZ) is characterized by (i) high amplitude reflections with an analogous phase to that of seafloor, possibly indicating potential porous sandstone‐rich turbidite reservoirs; (ii) BSRs showing polarity reversal relative to seafloor, suggesting higher impedance gas hydrates overlying lower impedance intervals with free gas; (iii) blanking reflections in fault zones, interpreted as gas‐bearing fluid conduits; (iv) strong reflections on the flanks of mud diapirs (e.g. flank drags) and above buried mud diapirs, demonstrating the presence of gas hydrates; (v) high amplitude reflections dragging on diapiric flanks with reversed phase to that of seafloor, indicating free gas ‐charged zones abutting mud diapirs; and (vi) the presence of focused advection and diffusion flow through mud diapirs and faults, which is interpreted to control the migration of thermogenic gas. Based on the distribution of seismic amplitude characteristics and reflection strength with respect to depth of the BSRs, hydrocarbon prospects can be divided into gas‐hydrate compartments above BSRs, free gas compartments above BSRs, and free gas compartments below BSRs. From a combination of geobody extraction and Monte Carlo simulation, the prospects appear to hold about 2048 Bcf (billion cubic feet) of total gas volume over a study area of 60 km2. These observations provide first‐order estimates of methane resources in the Lower Fangliao Basin offshore southwestern Taiwan.

Summary Glacial landforms identified in seismic 3D and multibeam data of the Barents Sea have improved the knowledge about past glaciations and associated geohazards. High-resolution P-Cable 3D seismic data were acquired in this area with an inline separation of 6 m, a source frequency range of 5–350 Hz and an source-receiver offset range of 120–160 m. Seabed images derived from the P-Cable data show an increased resolution and sharpness compared to images from conventional 3D seismic and multibeam echosounder data. High-resolution images of the buried Upper Regional Unconformity (URU) were derived from the P-Cable data, revealing previously unrecognized structures such as hill-hole pairs and rhombohedral and transverse ridges. These observations indicate different subglacial thermal regimes, the presence of permafrost, and a strong link with variations in the underlying geology. No reflections are imaged within the intraglacial sediment package in the conventional seismic data. However, reflections interpreted as the top of a shear margin moraine, shear planes, mass transport deposits, and soft beds are visible in the P-Cable data. Meter-scale glacial landforms and layers identified in the P-Cable cubes comprise new information about glacier dynamics, fluid flow, and faults, which are valuable for geotechnical and geohazard evaluations of offshore infrastructure.

Mass transport deposits (MTDs) were identified in Quaternary sedimentary sequences of the southern deep-water (water depth 1,000–1,500 m) region of the Qiongdongnan Basin, South China Sea. Based on high resolution 3D seismic data, seismic amplitude and coherence data are obtained and used to analyse MTDs. Through the seismic profile, two-way-travel time (TWT) time map, time thickness and time slice of target strata, profile characteristics and internal structure of MTDs are revealed. MTDs are characterized of mounded, hummocky, chaotic, low amplitude and discontinuous seismic reflection. MTD-internal thrusts and basal groove marks indicate mass-transport direction from WSW to ENE, suggesting MTD source in the shelf edge/upper slope system offshore central Vietnam, where mountainous rivers deliver high amount of terrigenous clastics. Since about 0.78–1.8 Ma, three depositional cycles characterized by basal MTDs overlain by turbidite channel levee systems have been emplaced in the study area. Timing and source of MTDs suggest a causal link between Quaternary high sedimentation rate to the shelf/upper slope in the Western South China Sea influenced by the eccentricity scale sea-level change and the emplacement of MTDs.

Basal shear zones of recurrent mass transport deposits serve as potential reservoirs for gas hydrates in the Central Canyon area, South China Sea

Submarine Mass Movements and Their Consequences

Three-dimensional (3D) seismic data from the southern Kumano Basin of southwest Japan image a nested series of moderately sized mass transport deposits (MTDs) that slid from a slope along the seaward side of the forearc basin. The deposits are dated to be approximately 0.3 to 0.9 Ma. These MTDs are likely linked to the movement along a prominent out-of-sequence thrust (OOST) fault, regionally steeper slopes that would have existed during deposition, and shifts in sedimentation over the past 0.9 Ma. The spatial resolution provided by the 3D seismic data permits the identification of kinematic characteristics and the internal geometries of the MTDs which total over 2.8 km3 in volume and cover more than 59 km2 of the seafloor at various stratigraphic levels. Each MTD is well imaged and exhibits various kinematic indicators while most of the basal glide planes and original headwall scarps above the deposits have been partially or fully eroded by subsequent MTDs. There are at least seven individual deposits that range in volume from 0.005 to 1.16 km3, in area from 0.2 to 21.8 km2; have runouts between 0.55 and 7.9 km, and generally translate downslope from the SE to NW. Basal, internal, and top surface kinematic indicators, such as grooves, thrust and fold systems, and pressure ridges, show that these MTDs originate from a prominent slide scar recognized in the high-resolution regional bathymetry. This, combined with a regionally shifting depocenter and faulting related to the earthquake cycle, points to regional tectonic activity as being the most likely failure trigger for these nested landslides.

Quaternary deposits in southern Orphan Basin include complex mass transport deposits (MTD) comprising both glaciogenic debris flows (GDF) and blocky MTD. 3D seismic reflection data were used to highlight the difference between the two types of MTD. The main MTD in southern Orphan Basin were sourced from the slope off Trinity Trough in the west of the basin. On the Trinity Trough-mouth Fan, a succession of GDF was deposited above horizon B5, interpreted to date from Marine Isotope Stage (MIS) 12. Beyond the direct influence of Trinity Trough, MTD unit 2 below horizon B5 is confined within pre-existing channels, which are in approximately the same location as the modern Bonanza Channel and Sheridan Channel. Blocky MTD are characterized by linear and divergent basal grooves and chaotic internal facies. Dispersed blocks, less than 1 km2 in area, are commonly present within the blocky MTD on the southern Orphan slope. The tongue of the main Sheridan MTD is sharp-edged, with a series of closely spaced pressure ridges. 3D seismic data of GDFs show few features diagnostic of blocky MTD. Both stacked GDF lobes and channelized GDF are observed on Trinity Trough-mouth Fan.

This paper describes the full cycle of 4D seismic data integration comprised of workflows related to 4D data analysis, quality control of reservoir models and reservoir model updating using both 4D seismic and well production data. These workflows are applied to a deepwater field, where high quality 4D seismic data is available. In the first step, we analyze 4D seismic data and extract multiple attributes to image changes in reservoir properties. Next, we apply different workflows which link 4D seismic data with the reservoir model. Finally, we update the reservoir model automatically by simultaneously honoring the 4D seismic and well production data. We use a novel approach which incorporates 4D seismic amplitude differences without explicitly modeling the full physics in a joint history matching workflow. Introduction Reservoir monitoring using 4D seismic data is becoming an increasingly important tool for reservoir management (Calvert, 2005). Nevertheless, the quantitative integration of both 4D seismic and historical production data into reservoir simulation models is a challenging task, which recently has become an active direction of research. Huang et al. (1997) applied a stochastic optimization method to minimize the mismatch between synthetic and observed seismic data over a reservoir to achieve simultaneous history-matching of 4D seismic and well-by-well production data. Landa (1997) proposed a gradient-based method to integrate both 4D seismic and pressure transient data. Stephen et al. (2006) developed a workflow for multiple-model history matching through simultaneous comparison of spatial information extracted from 4D seismic data as well as individual well-production data. Employing the Neigbourhood Algorithm (NA) as the sampling engine this workflow was applied to the North Sea Schiehallion field. Skjervheim et al. (2007) presented a version of the Ensemble Kalman Filter (EnKF) for continuous model updating capable to match a combination of production and 4D seismic data. They tested the method on a synthetic case and a North Sea field case. Jin et al. (2007, 2008) proposed the combination of the Very Fast Simulated Annealing (VFSA) method with pilot-point parameterization to solve the 4D seismic history-matching inverse problem and applied the workflow to a synthetic case. Castro (2006) proposed a probabilistic approach to perturb a high-resolution 3D geocellular model for integrating data from diverse sources, such as well logs, geological information, 3D/4D seismic, and production data. This workflow was successfully applied on a reservoir of the Oseberg field. Jin et al. (2011) also proposed a flood front based 4D seismic history matching workflow. In this paper, we present a case study of the full cycle of 4D seismic data integration ranging from basic and qualitative 4D attribute analysis to the advanced 4D seismic history matching workflow. 4D seismic attributes analysis This workflow provides an analysis of 4D seismic differences related to changes in reservoir properties. First, timeshifts between baseline and monitor 3D seismic volumes are computed through cross-correlation. Some initial data preparation usually takes place before the cross-correlation of the datasets, including automatic gain control and trace stacking for signal to noise ratio enhancement. Next, the computed timeshift is removed from the monitor survey in order to obtain meaningful 4D difference attributes. At that point, 4D seismic attributes can be extracted from a given gate around time horizons of interest - usually reservoir tops. For reservoirs with large lateral thickness change, top and base reservoir horizons should be used for attribute calculation. Different types of attributes can be extracted, such as the root mean square (RMS), the normalized RMS difference (NRMSD), etc.

Transversely-sourced mass-transport deposits and stratigraphic evolution of a foreland submarine channel system: Deep-water tertiary strata of the Austrian Molasse Basin

Machine learning is a tool that allows machines or intelligent systems to learn and get equipped to solve complex problems in predicting reliable outcome. The learning process consists of a set of computer algorithms that are employed to a small segment of data with a view to speed up realistic interpretation from entire data without extensive human intervention. Here we present an approach of supervised learning based on artificial neural network to automate the process of delineating structural distribution of Mass Transport Deposit (MTD) from 3D reflection seismic data. The responses, defined by a set of individual attributes, corresponding to the MTD, are computed from seismic volume and amalgamated them into a hybrid attribute. This generated new attribute, called as MTD Cube meta-attribute, does not only define the subsurface architecture of MTD distinctly but also reduces the human involvement thereby accelerating the process of interpretation. The system, after being fully trained, quality checked and validated, automatically delimits the structural geometry of MTDs within the Karewa prospect in northern Taranaki Basin off New Zealand, where MTDs are evidenced.