Facies, cyclicity and reservoir properties of the Lower Muschelkalk (Middle Triassic) in the NE Netherlands

Carbonate ramps are prolific hydrocarbon reservoirs, usually associated with grain-rich facies types. The present paper provides a sedimentological description and genetic interpretation of a gas reservoir located in mud-dominated carbonates. These deposits are part of the Lower Muschelkalk ramp sys...

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Veröffentlicht in:Facies 2002-01, Vol.46 (1), p.119-132
1. Verfasser: Poeppelreiter, Michael
Format: Artikel
Sprache:eng
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Zusammenfassung:Carbonate ramps are prolific hydrocarbon reservoirs, usually associated with grain-rich facies types. The present paper provides a sedimentological description and genetic interpretation of a gas reservoir located in mud-dominated carbonates. These deposits are part of the Lower Muschelkalk ramp system of Middle Triassic age. The Lower Muschelkalk carbonates can be subdivided into 6 main lithofacies: 1) bioturbated limestones 2) graded limestones 3) skeletal limestones 4) intraclast-rich limestones 5) heterolitic dolostones and 6) colored marlstones. These lithofacies are interpreted to represent the mid ramp to lagoonal section of a muddy, storm-dominated epeiric ramp. Facies are arranged into meter-thick small-scale cycles. These are composed of tight, bioturbated limestones at the base, which pass upward into low porosity graded limestones. Above occur graded dolostones with fair to good porosities. Tight, colored mudstones and marlstones cap the graded dolostones. These vertical facies successions represent a shallowing-up trend ranging from mid-ramp to inner ramp deposits. The small-scale cycles control reservoir architecture. Cycle base and top show low to no porosity while porous intervals are located in the middle part of the section. the decimeter-thick reservoir prone part of a cycle is due to the presence of graded layers composed of silt to very fine sand size micro-peloids, early dolomitisation and selective grain leaching. Reservior intervals are thin but numerous and up to 16 small-scale cycles are stacked on top of each other in the entire Lower Muschelkalk succession. Preliminary observations suggest reservoir layers to be sheet-like and regionally extended for at least several kilometers.[PUBLICATION ABSTRACT]
ISSN:0172-9179
1612-4820
DOI:10.1007/BF02668077