--> Abstract: A Tale of Two Valleys: Predicting Facies Architecture and Reservoir Quality in Incised Valley Fills, by L. F. Krystinik and D. A. Leckie; #91012 (1992).

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ABSTRACT: A Tale of Two Valleys: Predicting Facies Architecture and Reservoir Quality in Incised Valley Fills

KRYSTINIK, LEE F., Union Pacific Resources Co., Fort Worth, TX, and DALE A. LECKIE, Geological Survey of Canada, Calgary, Alberta, Canada

Incised valley fills are important exploration objectives, but are complex and elusive targets. Two end members for valley fills are narrow (<15 km wide) and broad (>15 km), each with predictable characteristics. We make the following sweeping generalizations for consideration.

Narrow valleys are straight to sinuous incisions cutting across flat shelves, opening onto linear coastlines. Lineaments and faults may control valley orientation. Tidal effects are variable in the estuary and do not always fully rework fluvial deposits. Up the valley, lateral migration of fluvial channels amalgamates sand bodies. High preservation potential and amalgamated fluvial sand produce greater reservoir continuity with potential for large stratigraphic traps where valleys run parallel to structural strike. Producing examples include Morrow Formation, CO; Yegua Formation, TX; Muddy Formation, WY; Glauconite and Viking formations, Alberta; and Bluesky Formation, British Columbia.

Broad valleys occupy structurally controlled depressions that form major embayments. Tidal amplification occurs in these embayments, and strong tidal currents can rework older fluvial or estuarine sediment to bedrock. The fill is complex and reservoir continuity can be low. Heterogeneity is caused by the diverse depositional environments within a large embayment and tidal reworking isolates sand into small pods encased in mudstone. Producing examples include the Kiskatinaw Formation, British Columbia, and Paddy Member, Alberta.

Although other factors strongly impact the complexity of valley fills, narrow valleys are preferred targets because they contain larger, laterally continuous, cleaner sandstone that can be followed long distances along the valley trend. In contrast, broad valleys contain numerous heterogeneous, isolated reservoirs with poor predictability.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)