Abstract Studies of turbidite channel complexes in outcrops, wells, and 3D seismic-reflection data suggest a general model of turbidite channel behavior related to three critical measures: (1) the thickness of channel elements; (2)the thickness of abandonment facies within each element; and (3) the thickness of overbank aggradation. These measures constrain channel stacking pattern and can be integrated into event-based geostatistical reservoir models that provide probabilistic predictions of net reservoir volume and element stacking pattern. Although channel and overbank thicknesses are measured routinely, this model provides a predictive framework that also emphasizes the importance of recognizing the presence and thickness of shale-rich abandonment facies at the top of sand-rich channel elements in outcrops. For a given flow composition, the deposits of thick channel elements (thickness of active fill plus abandonment facies) tend to have relatively low sand percentage, abundant bypass facies, and thick abandonment facies (underfilled channels). Underfilled channel elements with high topographic relief, from levee crest to channel thalweg, at the time of abandonment influence the location of subsequent elements, resulting in an organized channel stacking pattern. The deposits of relatively thin channel elements tend to have higher sand percentage, small volumes of bypass facies and thin/absent abandonment facies. Filled channel elements with low topographic relief at the time of abandonment had little influence on the location of subsequent elements, which resulted in a disorganized channel stacking pattern. Channel ‘‘relief ’’ corresponds to the depth of erosion plus the height of the levee crest above the initial sea floor. We observe that erosion relief can correlate strongly with downslope gradient. Flow composition also is critical because the rate of overbank aggradation is strongly influenced by mud volume. Muddy flows tend to produce thick overbank aggradation, high confinement, and under-filled channels with an organized stacking pattern. Sand-rich flows tend to produce relatively low overbank aggradation, low confinement (unless erosion relief is high), and filled channels with a disorganized stacking pattern.

Abstract Building geologically realistic reservoir models that honour well data and seismic-derived information remains a major challenge. Conventional variogram-based modelling techniques typically fail to capture complex geological structures while object-based techniques are limited by the amount of conditioning data. This paper presents new reservoir facies modelling tools that improve both model quality and efficiency relative to traditional geostatistical techniques. Geostatistical simulation using Multiple-Point Statistics (MPS) is an innovative depositional facies modelling technique that uses conceptual geological models as training images to integrate geological information into reservoir models. Replacing the two-point statistic variogram with multiple-point statistics extracted from a training image enables to model non-linear facies geobody shapes such as sinuous channels, and to capture complex spatial relationships between multiple facies. In addition, because the MPS algorithm is pixel-based, it can handle a large amount of conditioning data, including many wells, seismic data, facies proportion maps and curves, variable azimuth maps, and interpreted geobodies, thus reducing the uncertainty in facies spatial distribution. Facies Distribution Modelling (FDM) is a new technique to generate facies probability cubes from user-digitized depositional maps and cross-sections, well data, and vertical facies proportion curves. Facies probability cubes generated by FDM are used as soft constraints in MPS geostatistical modelling. They are critical, especially with sparse well data, to ensure that the spatial distribution of the simulated facies is consistent with the depositional facies interpretation of the field. A workflow combining MPS and FDM has been successfully used in Chevron to model important oilfield assets in both shallow- and deep-water depositional environments. Sedimentary environments can be characterized by a succession of deposition of elements, or rock bodies, through time. These elements are traditionally grouped into classes, commonly named ‘depositional facies’, based on their lithology, petrophysical properties, and biological structures. For example, the typical depositional facies encountered in fluvial environments are high permeability sand channels, with levées and crevasse splays, having a more variable range of permeability and net-to-gross ratio, within a background of low permeability shaley facies.

ABSTRACT Fluid-flow simulation results are used extensively as reservoir performance predictions upon which to base economics for reservoir management decisions. The generation of numerical models for simulation purposes may be easily facilitated by computer-aided algorithms, regardless of the quality of data or input parameters. This study contrasts two different geological interpretation styles: lithostratigraphic and chronostratigraphic. Specifically, comparisons are made as to properly integrating seismic-based information and to potentially erroneous conclusions deduced from simulator predictions if the simulation models are built without a sound geological framework. Models derived from the two different correlation strategies using only well logs are compared. Seismic inversions are included within the chronostratigraphic framework as a third model type. Multiple realizations of each model type are input to a fluid-flow simulator. Selecting the appropriate simulation results is closely tied to the reservoir management objective in question. Histograms of breakthrough times indicate little difference between the well-only models of either correlation strategy, whereas water displacement patterns are significantly different. Models that have been conditioned by the seismic pseudologs show substantially different results for both breakthrough and displacement distributions, and the spread or uncertainty in breakthrough estimates is greatly reduced compared to the well-only model results. A cloud transform method with correlated probability fields is introduced for stochastically estimating one model parameter (porosity) from another (impedance). This method allows incorporating the scatter in the relationship between the two parameters (crossplot).

Abstract Incised valleys associated with sequence boundaries of regional extent are present at two stratigraphic levels in Neoproterozoic siliciclastic rocks of northern and western Utah and southeastern Idaho. In comparison with many Phanerozoic examples, the sedimentary fill of these Neoproterozoic incised valleys is unusually coarse-grained. The most prominent paleovalley system is present along a sequence boundary in the upper part of the Caddy Canyon Quartzite, and may be traced from the Portneuf Range in southeastern Idaho south to the Canyon Range in central Utah and west to the Dugway Range in western Utah. Individual valleys range in depth from several meters to >45 m and in width from a few tens of meters to several hundred meters. Valley fills consist of diffusely to well stratified granule to pebble conglomerate characteristically containing siltstone clasts < cm to >2 m across. They are interpreted to have accumulated predominantly in a fluvial environment, and perhaps in part by debris flows in a subaerial or shallow estuarine setting. This paleodrainage system is of significance because it is one of the few documented examples of a widespread incised-valley system that erodes into an underlying fluvial braid plain more than 200 km in width, indicating that the effects of base-level changes were felt far upstream in the more proximal reaches of a braided fluvial system. A second incised valley with more than 60 m of local relief, and located at the sequence boundary at the base of the Geertsen Canyon Quartzite, is developed only locally in the Portneuf Range of southeastern Idaho. It is similar in both geometry and sedimentary fill to the valleys in the Caddy Canyon Quartzite, and is incised into the proximal reaches of a widespread fluvial braid plain. Somewhat shallower, conglomerate-filled valleys associated with higher-order cyclicity have been observed within the upper part of the Caddy Canyon Quartzite and overlying Inkom Formation, and, unlike the other examples, are encased in offshore marine siltstone. The development of Neoproterozoic sequence boundaries in the western U. S. is probably related to some combination of glacial eustasy (well documented in correlative strata elsewhere) and lithospheric extension, which appears to have preceded the development of the early Paleozoic passive continental margin. The relative roles of these mechanisms cannot yet be distinguished in the absence of more precise geochronology.

Abstract The distribution of Middle and Late Proterozoic sedimentary and metasedimentary cover that lies unconformably on Early Proterozoic and Archean crystalline basement has been known for decades, but recent work, employing techniques of paleomagnetic correlation, sedimentology, sequence stratigraphy, and analysis of tectonic subsidence has led to modifications of some long-accepted correlations and tectonic models. Within the context of both older classical studies and this new work, the stratigraphy, correlation, tectonic setting, fossil content, and mineral potential of Middle and Late Proterozoic rocks of parts of the Rocky Mountain, Colorado Plateau, and Basin and Range provinces of the United States are discussed. A problem common to interpretation of all Proterozoic strata is a widespread lack of fossil control on age and paleoecology, which makes correlations inherently uncertain and interpretation of depositional environments more difficult. We present current hypotheses about these topics and stress the uncertainty of some of our conclusions. The apparent polar wander path for the North American craton, as derived from the Middle and Late Proterozoic sedimentary cover, is central to our modifications of stratigraphie correlation, especially of Middle Proterozoic rocks. The reader is asked to view the work and summaries presented here in the light of ongoing scientific debate about strata that are chronically stubborn in yielding information. The authors of sections of this chapter include both those who have performed classical studies, which are the foundation of our present understanding, and younger geologists who have been busy refining and modifying early interpretations, using different methods of study. The treatment in this chapter is therefore variable depending on which generation of investigators is speaking.