--> --> Abstract: 3-D Architecture of Muddy Clinoforms: Control on the Distribution and Lateral Variation of Sedimentary and Reservoir Facies, Upper Cretaceous, Eastern Alberta, by Dallin P. Laycock, Per K. Pedersen, Ron Spencer, Steve Larter, Haiping Huang, and Andrew C. Aplin; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

3-D Architecture of Muddy Clinoforms: Control on the Distribution and Lateral Variation of Sedimentary and Reservoir Facies, Upper Cretaceous, Eastern Alberta

Dallin P. Laycock1; Per K. Pedersen1; Ron Spencer1; Steve Larter1; Haiping Huang1; Andrew C. Aplin1

(1) Geological Sciences, University of Calgary, Calgary, AB, Canada.

Shale dominated successions are often considered to be deposited through suspension fallout during periods of quiescence, so that such units are characterized by flat-lying or gently tapering stratal geometries. However, laboratory flume tank experiments show that mud can be transported in traction currents, and field studies document the presence of mud-rich clinoforms in both modern and ancient environments. In this paper we demonstrate that a thick, Cretaceous shale dominated succession is characterized by complex clinoform geometries with a large proportion of the mud deposited by traction current processes. The study presents one of the first accounts of how such clinoforms and mudstone facies control gas production from a shale-dominated succession.

The gas producing, shale dominated deposits of the Upper Colorado Group of central Alberta provide a unique area to investigate the depositional processes of fine-grained sediments and their resulting stratal geometries. Clinoforms have been identified within the mud-dominated upper Colorado Group on cross-sections of induction logs from closely spaced wells. Based on stratal geometries, the succession can be subdivided into “system tracts” according to seismic sequence stratigraphic principles. The stratigraphic surfaces which separate the systems tracts are demarcated in cores by shell lags, pebble lags, and glauconite rich horizons.

The geometric relationships of the clinoforms observed in the cross-sections demonstrate that the internal configuration of these mud dominated units is complex. Correlation of clinoforms provides important constraints on shale gas exploration, as each systems tract is characterized by a particular mudstone facies, shale composition, and organic content, and thus possesses unique shale gas reservoir properties. An examination of the production data shows that the production has historically been concentrated within specific systems tracts. As a result, a proper understanding of the clinoforms is crucial to mapping shale gas fairways. These clinoforms can be mapped in 3D, which allows for increased understanding of the clinoform geometries, and how those geometries relate to lateral and vertical facies variations. It is likely that there are mud-dominated units elsewhere in the world that have clinoform geometries that have previously gone unrecognized. As such, the clinoforms within the Upper Colorado Group could serve as an analogue for similar gas-bearing shales.