Seismic Time Slices Research Articles

Alluvial development during climate fluctuations depicted with spectral decomposition of the Middle Triassic to Lower Jurassic post‐rift succession in the Horda Platform (Norway) and the impact on reservoir properties

AbstractFor the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi‐humid, with increasingly fluctuating precipitation, controlled sedimentation, and run‐off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties

Combined inverse and forward numerical modelling for reconstruction of channel evolution and facies distributions in fluvial meander-belt deposits

The sedimentary record of meandering rivers contains a diverse and complex set of lithological heterogeneities, which impact natural resource management. Different methods exist to model such accumulated successions present in the subsurface by integrating knowledge of system evolutionary behaviour and geometries visible on seismic time or stratal slices. With reference to case-study examples, we review, discuss and employ two of these methods: (i) ChaRMigS generates possible scenarios for channel evolution and meander cut-offs by a reverse migration process; (ii) PB-SAND is a forward stratigraphic model which simulates fluvial point-bar geometry and facies distributions from known palaeo-channel geometries. We introduce a workflow to demonstrate how these two methods can be applied in combination to predict fluvial meander-belt facies distributions, using a subsurface dataset on a Pleistocene succession from the Gulf of Thailand where abandoned channels are visible on seismic time slices, but for which bar-accretion geometries and the exact timing of channel abandonment are unclear. Results show the value of a combined modelling approach to automate the stochastic generation of facies distributions constrained by seismic interpretations.

PETROPHYSICAL AND ROCK PHYSICS ANALYSES FOR CHARACTERIZATION OF COMPLEX SANDS IN DEEPWATER NIGER DELTA, NIGERIA

Characterization of complex sand reservoirs in deepwater of Niger Delta was carried out through petrophysical and rock physics evaluation of well log data from three wells. Petrophysical analysis to determine clay volume, porosity, lithologies, and hydrocarbon saturation were made. Rock physics was studied in a velocity-porosity plane to analyze the influence of depositional and diagenetic features on the reservoirs. Cross-plots of different elastic parameters, using linear regression and cluster analysis, were generated for lithologic and fluid fill identification and to differentiate between the hydrocarbon bearing sands, brine sands, and shale. Variance attribute was extracted on seismic time slice in order to image the complex sand distribution in the area. Three reservoirs of turbidite origin were identified within the upper fan to lower fan area. Petrophysical results revealed gas bearing reservoir units with less than 20% shale volume and porosity of 25-31%. Lambda-Mu-Rho (LMR) cross-plots for the reservoirs show gas saturated data cloud and trend. Ratio-Difference (R-D) cluster analysis of elastic rock properties shows a distinct trend and data cloud that represents lithofacies units and fluid fills. The study concludes that the reservoirs simulated contact cement and friable models with properties that ranged from highly porous, well sorted and poorly consolidated sand to fairly sorted and highly cemented sands. The results provide a model that increases the possibility of finding reservoir sand while mitigating the risk involved in finding hydrocarbons. Keywords: Rock Physics, Petrophysics, Deepwater, Reservoir, Niger Delta, Cross-plot http://doi.org/10.35180/gse-2019-0009

Reconstructing basin-scale drainage dynamics with regional subsurface mapping and channel-bar scaling, Aptian, Western Canada Foreland Basin

An extensive subsurface dataset from the Lower Cretaceous McMurray Formation of northeastern Alberta, Canada, is leveraged to provide new insights into the Aptian drainage arrangement of the Western Canada Foreland Basin. Regional-scale stratigraphic mapping is supplemented with paleodrainage area estimates obtained using quantitative relationships between fluvial bankfull flow depth and drainage area in order to reconstruct paleocatchments, including those of a continental-scale river system and its tributaries. Using channel geometries delineated in high-resolution 3D seismic time slices, we test for evidence of a tidal prism within Aptian-aged drainage systems in order to assess the applicability of fluvial scaling relationships to the McMurray Formation.Refined paleogeographic reconstructions incorporate catchment estimates for the southerly-sourced trunk drainage system of the McMurray Formation, which corroborate the claim that the unit was associated with a continental-scale drainage network. Drainage area estimates for southwesterly-sourced tributary systems are, however, up to an order of magnitude smaller. These tributaries likely had headwaters in the North American Cordillera. This work demonstrates the applicability of combining regional mapping, sedimentological analysis, and fluvial scaling relationships to reconstruct sediment-routing systems from source-to-sink in the deep time record.

Channel edge detection using 2D complex shearlet transform: a case study from the South Caspian Sea

Channels are important sedimentary features in hydrocarbon plays either as targets for drilling or geohazards that should be avoided, depending on burial depth and fluid-fill. Either way, for well design purposes it is important to image channels before drilling. Shearlet transform, as a multi-scale and multi-directional transformation, is capable of detecting anisotropic singularities in two and higher dimensional data. In this study, the complex-valued shearlet-based edge measure was implemented for the aim of channel boundary detection. The method was applied to synthetic seismic time-slices containing channels with different signal-to-noise ratios as well as a real time-slice from the South Caspian Sea. The performance of the shearlet-based algorithm was compared both qualitatively and quantitatively with well known gradient-based edge detectors such as Sobel and Canny, resulting in successfully localising edges and detecting less false positives.

THE EVOLUTION OF CHANNEL SYSTEM IN THE NORTHEAST MALAY BASIN, TERENGGANU OFFSHORE

This study aims to evaluate the evolution of the channel system in the Pleistocene-Recent succession in the northeast Malay Basin based on channel morphologies. The variable types of channel morphologies were determined from seven seismic time slices of study area. The fluvial channel became wider and low-sinuous when the sea-level rise. Meanwhile, the fluvial channel became narrower and high-sinuous when sea levels decreased. The point bars are seen in the meandering curve of the high-sinuosity channel. This occurred because of the sea-level decrease and more sediment being deposited in the study area. The point bars morphology do not appear in the transgressive event. An oxbow lake appeared in the 525 ms seismic time slice and is labelled as the oldest channel system. The channel morphologies then changed, and the oxbow lake does not appear in the younger system channel (Recent). The channel morphology changes have been proven to be affected by global sea-level changes.

Semiautomatic interpretation of 3D sedimentological structures on geologic images: An object-based approach

The characterization of sedimentary structures is an important step in constructing quantitative models of sedimentary deposits from digital images, such as 3D seismic data, satellite images, or digital outcrops. However, the interpretation of these structures generally consists of tedious line pickings followed by surface modeling to define geobodies. Automatic geobody extraction is an alternative, but it is sensitive to image noise, and it does not account for prior sedimentary knowledge. We decided to combine minimal picking by an interpreter with object-guided image processing and optimization to achieve fast and semiautomatic geobody interpretation. Our approach used a realistic volumetric geobody representation based on nonuniform rational basis splines, which can easily be deformed by the interpreter and numerical optimization. Custom edge detection guided by some initial rough interpretations was performed to strengthen the most relevant edges in the picture. Automatic optimization was then computed to fit the initial geobody to these highlighted edges. This approach was applied on satellite pictures showing alluvial channels, and some preliminary results on 3D seismic time slices were also presented. The interpreted channels were then used in a retrodeformation process to automatically reconstruct the point bars. This semiautomatic method opens new perspectives to help interpreters rapidly come up with 3D models of sedimentary structures from subsurface and analog surface data sets.

Imaging subtle faults using azimuthal coherence attribute: A case study from Central Saudi Arabia

ABSTRACT The coherence attribute is an edge detection method that is widely used for interpreting faults on 3-D seismic time slices. The traditional coherence attribute is calculated on migrated volumes using traces from all available azimuths. It has recently been shown that calculating coherence along specific azimuths can enhance the detection of faults running perpendicular to those azimuths. In this study, we applied azimuthal coherence attribute analysis on a 3-D seismic data set from a gas field in Central Saudi Arabia. We generated four migrated 3-D data volumes sorted by azimuth in addition to a conventional full-azimuth volume. We then calculated the coherence attribute for all volumes and compared each azimuthal coherence volume to the conventional full-azimuth coherence volume. The azimuthal coherence results exhibited an improved definition for faults whose strikes are perpendicular to the sorting azimuth. More specifically, systems of NW-trending discontinuities were imaged more clearly in the NE-SW oriented coherence volume than it was in the full-azimuth coherence volume. The reason for this enhancement is the fact that seismic waves tend to avoid passing through the fault when they propagate parallel to the fault strike therefore missing the effects of the fault while they must pass through the fault when propagating perpendicular to the fault strike which results in better illumination of the fault.

Seismic geomorphology and sedimentology of a tidally influenced river deposit, Lower Cretaceous Athabasca oil sands, Alberta, Canada

The bitumen of the Lower Cretaceous McMurray Formation in Alberta arguably represents one of the most important hydrocarbon accumulations in the world. In-situ development relies on heat transfer through the reservoir via horizontal steam injection wells placed 4 to 6 m (13–20 ft) above horizontal producers near the base of the sandstone reservoirs. Given this technology, understanding the distribution of the resource is paramount for a successful development program. Sedimentary facies provide a direct control on bitumen distribution and recovery. Most facies models developed to describe and predict sedimentary units of the McMurray Formation consider fluvial, estuarine, and/or deltaic depositional settings. In-situ development, however, requires a particularly high-resolution sedimentologic interpretation. High-quality three-dimensional seismic reflection data and extensive drill cores from acreage located approximately 50 km (31 mi) south of Fort McMurray provide important insights into the sedimentologic organization of reservoir and nonreservoir deposits in the upper one third (40 m [131 ft]) of the reservoir interval. Geomorphologic characteristics of the strata observed in seismic time slices reveal that a fluvial depositional setting was prevalent. Ichnologic and palynologic data, as well as sedimentary structures suggestive of tidal processes, indicate a marine influence in the upper reaches of a fluvial system characterized by channels that were 390 to 640 m (1280–2100 ft) wide and 28 to 36 m (92–118 ft) deep. The complex stratigraphic architecture consists of a mosaic of large-scale depositional elements, including abandoned channels or oxbow lake fills, point bars associated with lateral accretion, point bars associated with downstream accretion, counter point bars, and sandstone-filled channels. Reservoir deposits are primarily associated with point bars and sandstone-filled channels.

Sedimentology and stratigraphic architecture of a point bar deposit, Lower Cretaceous McMurray Formation, Alberta, Canada

Abstract A single channel and point bar deposit are examined in the subsurface of northeastern Alberta from the Lower Cretaceous McMurray Formation. High-quality 3-D seismic, core and wireline log data were used in order to constrain the stratigraphic architecture and the facies distribution. Mudstone-dominated abandoned channel fill provides a mold of the 32–36 m deep paleo-channel; seismic time slices reveal that these channels were 500–584 m wide. The associated point bar deposit ranges in thickness from 30–40 m. Seven facies are identified in the point bar strata studied, including massive sandstone with siltstone rip-up clasts at the base of the point bar sequence, cross-stratified sandstone that is common in upstream locations on the point bar, various interbedded sandstone and siltstone units that comprise IHS packages, and siltstone. Reservoir quality in the McMurray Formation is directly related to numerous factors, including the overall thickness of bar deposits, and the distribution of siltstone beds that can act as barriers or baffles to fluid flow. The overall thickness of the point bar deposit studied is greatest where increased scour around the apex of the paleo-channel bend resulted in increased accommodation; amalgamated sandstone units are up to 23–30 m thick in these areas. Stratigraphic cross-sections and mapping of lithological trends across the point bar deposit demonstrate that siltstone beds increase in abundance upward through the section, and in downstream reaches of the point bar. The average cumulative thickness of siltstone beds increases from 18 cm to 67 cm in the downstream direction, which corresponds to a decrease in siltstone bed frequency. Small-scale upward-fining packages that range from 5–12 m thick are locally observed within the point bar deposit, and are interpreted to represent erosion and reactivation following storm events or episodes of meander-bend rotation.

Ultra-high-resolution marine 2D–3D seismic investigation of the Liman Tepe/Karantina Island archaeological site (Urla/Turkey)

2D and 3D high-resolution seismic investigations were performed on submerged coastal archaeological sites at Iskele and near to Karantina Island in the Bay of Izmir in western Turkey. Tectonic subsidence of the coastline has submerged a number of archaeological features associated with an important Early Bronze Archaic settlement (Liman Tepe) and the classical Ionian city of Clazomenae. Seismic surveys were focused on imaging of an Archaic harbour structure and other submerged Hellenistic and Roman architectural features. Seismic data were acquired with the SEAMAP-3D ultra-high-resolution 3D marine seismic acquisition system developed for detailed archaeological site investigation. A 2D reconnaissance survey was performed over a 2 km 2 area around Karantina Island to evaluate the seismic penetrability and to locate sites for further 3D investigation. This survey predominantly revealed marine sediment layers covering the local bedrock, which is characterized by scattering of seismic energy showing its rocky nature. Two ultra-high-resolution 3D seismic surveys were performed. The first covered a 350 m × 30 m area in the modern harbour targeting a prominent Archaic harbour structure. The second was acquired across a 120 m × 40 m area on the southeast shore of the Karantina Island close to a Roman architectural feature. The 3D surveys were acquired with nominal line spacings of 1 m, using a 8 × 4 pseudo-rigid hydrophone array and a Boomer source firing at 3 Hz shot frequency. Automated processing of the seismic data using a portable Linux cluster provided stacked 3D seismic volumes with 25 cm × 25 cm bin size on-site. The 3D seismic survey of the harbour clearly imaged the submerged Archaic structure and the underlying sediment sequence. The seismic time slices reveal two seismic anomalies (2–3 m in diameter) in the harbour basin sediments. The 3D surveys southeast of Karantina identified a thicker marine sediment sequence overlying steeply dipping bedrock reflectors. The sediment sequence records the rapid accumulation and progradation of the coastline following the construction the Alexander causeway linking the mainland with the island in 334 B.C.

Slump Dominated Upper Slope Reservoir Facies, Intra Qua Iboe (Pliocene), Edop Field, Offshore Nigeria: ABSTRACT

An integration of sedimentologic and 3D seismic data provides a basis for unraveling complex depositional processes and sand distribution of the Intra Qua Iboe (IQI) reservoir (Pliocene), Edop Field, offshore Nigeria. Nearly 3,000 feet of conventional core was examined in interpreting slump/slide/debris flow, bottom current, turbidity current, pelagic/hemipelagic, wave and tide dominated facies. The IQI was deposited on an upper slope in close proximity to the shelf edge. Through time, as the shelf edge migrated seaward, deposition began with a turbidite channel dominated slope system (IQI 1 and 2) and progressed through a slump/debris flow dominated slope system (IQI 3, the principal reservoir) to a tide and wave dominated, collapsed shelf-edge deltaic system (IQI 4). Using seismic time slices and corresponding depositional facies in the core, a sandy {open_quotes}fairway{open_quotes} has been delineated in the IQI 3. Because of differences in stacking patterns of sandy and muddy slump intervals, seismic facies show: (1) both sheet-like and mounded external forms (geometries), and (2) parallel/continuous as well as chaotic/hummocky internal reflections. In wireline logs, slump facies exhibits blocky, coarsening-up, fining-up, and serrated motifs. In the absence of conventional core, slump facies may be misinterpreted and even miscorrelated because seismic facies and log motifsmore » of slumps and debris flows tend to mimic properties of turbidite fan deposits. The slump dominated reservoir facies is composed of unconsolidated fine-grained sand. Thickness of individual units varies from 1 to 34 feet, but amalgamated intervals reach a thickness of up to 70 feet and apparently form connected sand bodies. Porosity commonly ranges from 20 to 35%. Horizontal permeability commonly ranges from 1,000 to 3,000 md.« less

The instantaneous-phase time slice: A crucial display for enhancing 3-D interpretation

Instantaneous-phase is the optimum attribute to use in horizontal seismic time slices for rapid, accurate 3-D structural mapping, because of its enhancement of event continuity. Instantaneous-phase slices also provide the interpreter with the most precise display for directly interpreting spatial relationships between seismic sequences, by reasoning analagous to that used to interpret geological maps. In contrast, amplitude time slices lack precision because weak events are lost by scaling, and wavelet phase points can only be crudely estimated.