Abstract Sequence stratigraphy is a method to systematically place key stratal observations into a chronostratigraphic framework for more accurate predictions away from control points. The depositional sequence is its basic unit, defined as “a stratigraphic unit composed of a relatively conformable succession of genetically related strata and bounded at its top and base by unconformities or their correlative surfaces” ( Abreu et al., 2014 modified from Mitchum et. al., 1977a ), which forms as a result of transgressions and regressions. Sequence stratigraphy is first and foremost a method that guides observations in the stratigraphic record across an array of depositional settings, stratal attributes, and data sets, explicitly recognizing that the stratigraphic record is comprised of both rocks and surfaces in various forms. These observations are then summarized in models that generalize details to facilitate prediction away from data control points. For completeness, sometimes the models are interpreted in terms of mechanisms (e.g., eustasy, climate, etc.) that may help explain observations and enhance prediction. The accommodation succession method of sequence stratigraphy ( Neal and Abreu, 2009 ) assumes that these building blocks form in response to varying rates of coastal accommodation increase and decrease (δΑ) relative to the rate of sediment flux (δS).

Abstract Canada’s largest bitumen resource is contained within the McMurray Formation, a complex deepening-upward fluvial-estuarine succession typified by abrupt facies changes, inclined stratal geometries, and high-relief unconformities. Within this succession, fluvial-estuarine point-bar reservoirs represent a significant fraction of the resource that can be developed through surface mining and in-situ thermal recovery processes such as steam-assisted gravity drainage (SAGD). At Syncrude Canada Ltd.’s Mildred Lakemine, closely spaced core-hole data are tied to high-wall exposures of a point-bar succession that is 55m (180 ft) thick and occupies an area of at least 15 km 2 (6 mi 2 ). Data are integrated using two 3-D visualization tools: light detection and ranging (LIDAR), a laser technology that produces high-resolution digital terrain models of the outcrop, and LogVu3D, an application that displays large sets of geophysical logs in a 3-D volume. The point-bar model developed here describes sand body dimensions, stratal stacking patterns, lithofacies distributions, and mudstone heterogeneity at a variety of scales. A conceptual model of steam chamber growth in a heterogeneous point bar is presented that has implications for steam chamber definition, resource assessment, reservoir modeling, and development well planning.

Abstract A commonly assumed element of sequence stratigraphic theory is that incised valleys must feed lowstand deltas. This model persists despite examples in which no lowstand deposit is present at the distal ends of some ancient and recent valley fills. The Clearwater Formation at Cold Lake Field, Alberta, Canada, presents a unique opportunity to investigate in detail the transition from fluvial incised-valley fills to open marine mudstone using over 1000 wells, over 400 with core, from an area of 3,200 km 2 . The presence of prominent marine well-log markers and the abundance and density of well logs allows confident correlation of the incised-valley fills. The Clearwater Formation consists of 13 stacked incised valleys with depths of incision ranging from 30 m to possibly 120 m. All of the valley fills show a depositional facies pattern from sandy fluvial or upper estuarine updip to muddy estuarine or marine deposits downdip. All of the valleys terminate downdip as thin (< 2 m) sheets of marine sandy mudstone. Significantly, none of the valleys are connected to downdip lowstand deltas, or even sandy lowstand shorelines. In addition, the valley-fill lithofacies differ significantly from the marine strata into which they are incised; they are sandier, and the sand fraction is coarser. The valley fills, therefore, are not composed only of reworked material eroded from valley walls, but represent sediment delivered from more proximal sources, presumably by rivers. Our examples demonstrate that the presence of deep incised valleys, even if they are filled with coarse material, cannot by itself be used to predict sand delivery to the paleo-shoreline or more basinward regions. We recognize two primary conditions for valley fills that lack associated sandy lowstand deposits: the lowest point of relative sea level was above the continental shelf edge (for passive-margin settings), and sediment delivery during early rising sea level was limited. For the examples cited we interpret that filling of incised valleys occurs during relative sea-level rise when only limited amounts of sediment can be delivered beyond incised-valley mouths.

Abstract A new sequence-stratigraphic framework is proposed for the Burgan and Mauddud formations (Albian) of Kuwait. This framework is based on the integration of core, well-log, and biostratigraphic data, as well as seismic interpretation from giant oil fields of Kuwait. The Lower Cretaceous Burgan and Mauddud formations form two third-order composite sequences, the older of which constitutes the lowstand, trans-gressive, and highstand sequence sets of the Burgan Formation. This composite sequence is subdivided into 14 high-frequency, depositional sequences that are characterized by tidal-influenced, marginal-marine deposits in northeast Kuwait that grade into fluvial-dominated, continental deposits to the southwest. The younger composite sequence consists of the lowstand sequence set of the uppermost Burgan Formation and transgressive and highstand sequence sets of the overlying Mauddud Formation. This composite sequence is sand prone and mud prone in southern and southwestern Kuwait and is carbonate prone in northern and northeastern Kuwait. The lowstand sequence set deposits of the Burgan Formation are subdivided into five high-frequency depositional sequences, which are composed of tidal-influenced, marginal-marine deposits in northeastern Kuwait that change facies to fluvial-dominated deposits in southwestern Kuwait. The transgressive and highstand sequence sets of the Mauddud Formation are subdivided into eight high-frequency, depositional sequences. The Mauddud transgressive sequence set displays a lateral change in lithology from limestone in northern Kuwait to siliciclastic deposits in southern and southwestern Kuwait. The traditional lithostratigraphic Burgan-Mauddud contact is time transgressive. The Mauddud highstand sequence set is carbonate prone and thins south- and southwestward because of depositional thinning. Significant postdepositional erosion occurs at the contact with the overlying Cenomanian Wara Shale. The proposed sequence-stratigraphic framework and the incorporation of a depositional facies scheme tied to the sequence-stratigraphic architecture allow for an improved prediction of reservoir and seal distribution, as well as reservoir quality away from well control.

ABSTRACT Stratigraphic interpretation from wireline logs is typically drawn from multiple log traces or from crossplots of log data. Both techniques can readily depict vertical changes in lithology or reservoir quality, but lateral relationships are not readily visualized. Significant improvement in the geologic interpretation of wireline log data can be achieved through transformation and treatment of the transformed data as “seismic” traces for the purposes of processing, interpretation, and display. This combination of wireline logs with a seismic interpretive approach is labeled pseudoseismic. The pseudoseismic transform can combine data from multiple logging tools, generating a convolved ‘crossplot log’ for each well. A well-designed transformation of wireline log data across multiple wells maximizes both spatial and compositional information contents and provides a readily interpretable image of the subsurface geology. Various filters and transformations can be applied to emphasize different aspects of the subsurface geology. The transformed wireline log data are loaded into a computer workstation and interpreted as a set of 2D pseudoscismic traces or as a 3D pseudoseismic volume. Use of interpretation and visualization packages developed for seismic data offers flexibility in displaying and picking horizons, and increased efficiency of sequence stratigraphic interpretation. The treatment of wireline logs as a data volume permits comprehensive and cost-effective sequence stratigraphic and reservoir analysis of data sets that were previously considered intractable. Examples from western Kansas, at both the regional and field scale, illustrate the utility and efficiency of sequence stratigraphic interpretation using the pseudoseismic approach. The pseudoseismic approach to the analysis of wireline log data from multiple wells opens new dimensions in log interpretation and provides significant insight into complex stratigraphic geometries associated with lithology, reservoir quality, and fluids.

Abstract The Douglas Group (Stephanian) of eastern Kansas contains several paleovalleys that were eroded during falling sea level and filled during lowstands and subsequent transgressions. One paleovalley exhibits 34 m of incision, is approximately 32 km in width, and can be laterally traced along outcrop and into the subsurface to the south for approximately 140 km. A fluvial to estuarine to marine facies mosaic can be delineated both laterally, from north to south, as well as within individual vertical sections. Paleovalleys were filled with a fining upward succession; the lowest facies is cross-bedded conglomerate and sandstone. The conglomerate contains clasts and fossils eroded from older units exposed within the paleovalley. Sandstone beds exhibit large scale (up to 1 m thick) trough and tabular-planar cross beds. Paleocurrent directions are generally southwest and indicate deposition via large-scale fluvial systems that were constrained within the paleovalleys. Overlying the fluvial sandstone is a diverse suite of lithofacies including planar-bedded sandstones and siltstones, heterolithic facies, sheet-like sandstone, bioturbated sandstones, and marine facies. The planar-bedded sandstones and siltstones can exhibit neap-spring tidal cycles which were formed in high-intertidal settings. Heterolithic facies are typically laminated and contain pinstripe laminations, starved ripples, and well-developed tidal cycles (cyclical tidal rhythmites). Neap-spring tidal cycles are common and range from 1 cm in thickness in heterolithic facies to as much as 1 m in thickness in planar-bedded siltstones. An interpretation invoking very high localized depositional rates is substantiated by the presence of buried upright trees, some of which have attached foliage. Tidal rhythmites are well developed in siliciclastic facies immediately overlying coals. The heterolithic and silty rhythmites were apparently developed within the estuarine turbidity maximum where high turbidity and locally high depositional rates resulted from estuarine circulation patterns and tidal amplification. The sheet-like sandstone bodies are dominated by small-scale trough crossbedding and ripple- and planar laminations. Paleocurrents are bimodal to the southwest and northeast, reflecting ebb- and flood-tidal currents. Features such as flat-topped ripples, rain-drop imprints, and tetrapod trackways indicate deposition within the intertidal zone. Estuarine to marine sequences contain progressively higher diversities of biogenic structures. "Flaggy" bioturbated sandstones indicate significant marine influences. These sandstones are capped by widespread marine shales and limestones that extend far beyond the limits of paleovalleys. Shales can be extensively bioturbated, lack laminations, and locally contain marine body fossils. Limestones form widespread lithostratigraphic markers and contain abundant marine fossils such as bivalves, fusulinids, brachiopods, crinoids, and bryozoans. Some of the limestones consist of shelly lags which indicate the development of transgressive surfaces of erosion. There are two major sequences developed within the Douglas Group. The sequence boundaries can be placed at the contact between incised fluvial sandstones and eroded underlying, commonly marine, strata. The fluvial and estuarine facies were deposited during lowstand and subsequent sea-level rise. The highstand system includes marine shales and limestones which were erosionally incised during subsequent fall in sea level.