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Conceptual model for predicting mudstone dimensions in sandy braided-river reservoirs

Ranie Lynds and Elizabeth Hajek
Conceptual model for predicting mudstone dimensions in sandy braided-river reservoirs
AAPG Bulletin (August 2006) 90 (8): 1273-1288

Abstract

Sandy braided-river deposits with high net-to-gross sand ratios are commonly attractive reservoirs, yet internal lithologic heterogeneities, particularly the presence of low-permeability mudstone deposits, significantly complicate the development of such units. Previous work has focused on measuring the scale and distribution of mudstone deposits in outcrop analogs; however, because of extreme differences in scale, discharge, sediment load, and geologic history, the results of these studies are difficult to apply with confidence to a wide range of sandy braided-river reservoirs. Based on work in modern braided rivers (Niobrara and North Loup rivers, Nebraska) and ancient braided-river deposits (Kayenta Formation, Jurassic and lower Castlegate Sandstone, Cretaceous, Colorado and Utah), we propose a process-based conceptual model for understanding and predicting the distribution and geometries of fine-grained (mudstone) intervals in sandy braided-river deposits. This model is an idealized channel-fill unit composed of five fine-grained lithofacies (mud plugs, channel-lining muds, interbar muds, inclined heterolithic strata, and flood-plain and overbank material) that scale proportional to channel-thread dimensions, including depth, cross-stream width, and downstream length. Each lithofacies is found in a different region in an individual channel fill, and lithofacies found low in a fill may be preferentially preserved. Within braided-river deposits, extrinsic depositional factors, such as aggradation rate, available accommodation, and avulsion-return time, produce different channel-fill stacking arrangements, preserving fine-grained lithofacies in different, relative proportions. This conceptual model provides an approach to reservoir characterization that deductively constrains the dimensions and distribution of fine-grained barriers to flow and may help account for the inherent variability in sandy braided-river deposits.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 90
Serial Issue: 8
Title: Conceptual model for predicting mudstone dimensions in sandy braided-river reservoirs
Affiliation: University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
Pages: 1273-1288
Published: 200608
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 63
Accession Number: 2006-071421
Categories: StratigraphyEconomic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N37°00'00" - N41°00'00", W109°00'00" - W102°00'00"
N40°00'00" - N43°00'00", W104°04'60" - W95°19'60"
N37°00'00" - N42°00'00", W114°04'60" - W109°04'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 200641
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