Predicting Tidal Sand Reservoir Architecture Using Data from Modern and Ancient Depositional Systems
Lesli J. Wood, 2004. "Predicting Tidal Sand Reservoir Architecture Using Data from Modern and Ancient Depositional Systems", Integration of Outcrop and Modern Analogs in Reservoir Modeling, G. Michael Grammer, Paul M. “Mitch” Harris, Gregor P. Eberli
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Tidal sandbanks make up most reservoir-quality rock volume in hydrocarbon fields characterized by tidally influenced deposits. Predicting the three-dimensional architecture and petrophysical character of these elements is critical to a proper assessment of a field’s recoverable hydrocarbon potential. Most of these fields are under development or even in stages of secondary or tertiary recovery that require accurate flow-simulation and resource-distribution models.
Modern tidal settings and ancient tidal deposits provide dimensional and architectural data that can significantly reduce our uncertainty in constructing realistic reservoir models of these tidal-bank systems, improve our ability to estimate probability of exploration success, and help us evaluate correlation lengths between subsurface wells and lower-resolution seismic data. Modern tidal banks can be found in many depositional settings, from shallow estuaries to the outer continental shelf. Deep submarine canyons on the outer shelf strongly influence the shelf tidal processes by establishing a geomorphic link between deep-ocean and shallow-ocean currents. These interacting processes, in turn, influence the distribution of tidal banks. Banks that develop in shelf locations are thick, broad, and asymmetric, with linear forms distributed radially around the current or sediment source. Banks that develop in estuaries are thin, narrow, and symmetric, with parabolic forms or bar chains lying parallel to the estuary walls.
Ancient tidal banks from the Sego Sandstone (upper Campanian) in eastern Utah show a distinct organization of different dimensions between systems tracts and sequences. Falling-stage tidal bars and ridges are shorter and wider than transgressive tidal bars and ridges, a difference attributed to increased sediment supplies, decreased water depths, and increased energy conditions associated with base-level fall.
Cumulative-probability curves provide the format for using modern and ancient systems’ architectural data on tidal-bank dimensions to estimate the probability that certain bank dimensions may occur in ancient deposits. Cumulative-probability curves show that the P50 for worldwide tidal-bank length is 12,000 m, width is 1600 m, and height is 9.2 m. These curves provide the means to assess the probability of correlation between wells of varying distances as well as the likelihood of resolving tidal banks in seismic data at varying resolutions.
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Building robust 3-D reservoir models is a major challenge that requires incorporation of geologically defined input parameters. This publication provides an overview of current approaches used in the development of geologically constrained and integrated reservoir models. Each of the 18 papers addresses various stages in the process of creating a reservoir model through the development and incorporation of an analog, extracting the quantitative input parameters on lateral and vertical variability, and the development and modification of a 3-D reservoir model based upon geologically constrained data. This applied volume is divided into two sections. The first is a set of papers illustrating the value and methodology of acquiring geometrical data on the lateral and vertical distribution of reservoir facies, within a sequence stratigraphic framework, using both outcrop analogs and detailed study of modern depositional systems. The second section includes both case studies where outcrop and modern analog data have been incorporated into subsurface reservoir models, as well as papers that illustrate recent advances in simulation and geostatistical methodologies. Together, the two sections provide a comprehensive look at integrated reservoir modeling.