Upper Muschelkalk (Middle Triassic) carbonates produce natural gas at Coevorden field in the NE Netherlands. This is currently the only field which produces gas from this succession although several other prospects have been identified nearby. In order to help develop these hydrocarbons, this study proposes a facies and reservoir model of the Upper Muschelkalk in the NE Netherlands together with a regional framework intended to assist in further evaluation. Distribution of facies and reservoir properties of the Upper Muschelkalk carbonates in the NE Netherlands indicate deposition on a storm‐dominated epeiric ramp with a very low gradient. The predominantly muddy and marly lithofacies types in proximal and distal parts of the ramp gradually interfinger with a shoreline‐detached “shoal”‐like ooidal grainstone complex. The best reservoir quality (permeability up to 60 mD) is recognised within dolomitised peloid ooid grainstones. These are interpreted as high‐energy backshoal deposits. Reservoir quality decreases in the limestone‐dominated “shoal” facies and the muddier foreshoal facies. A four‐fold hierarchy of depositional cycles describes the systematic and thus predictable vertical variation in reservoir quality (permeability) and quantity (net‐to‐gross). High‐resolution correlation suggests that medium‐scale cycles (5 to 15 metres thick) can be traced for hundreds of kilometres. Small‐scale cycles (1 to 3 metres thick) are persistent for several tens of kilometres and have sheet‐like geometries. Individual reservoir units (several decimetres thick) appear to be laterally continuous over a maximum of a few kilometres although internal flow barriers might be expected. Mapping of Upper Muschelkalk thickness and facies has clearly defined backshoal, ”shoal and foreshoal facies belts with distinctly different reservoir characteristics. Typically, reservoir quality and quantity decrease with increasing thickness of the Upper Muschelkalk and the underlying Middle Muschelkalk halite. The systematic variations in thickness are apparently controlled by a combination of palaeogeography and palaeotectonics. The best reservoir quality and highest quantity is found on a palaeohigh characterised by a relatively thin Upper Muschelkalk succession and the absence of underlying halite. These features can also be recognised in seismic data. The results of this case study can also be applied in the integrated characterisation of similar epeiric carbonates constituting highly productive reservoirs in the Middle East, including the Khuff and Arab Formations.

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Ravi Borkhataria studied geology at the University of Darmstadt, Germany, and received his Ph.D. from the University of Tü bingen, Germany, in 2004, carrying out a multiyear, discipline-bridging reservoir-characterization project for Nederlandse Aardolie Maatschappij B.V. (NAM)/Shell. He is currently working as a geologist in the Shell Carbonate Team in Rijswijk, Netherlands. His research interests include evolution of carbonate-evaporite basins and stratigraphic reservoir prediction in carbonate systems.

The Triassic Muschelkalkc arbonatesareauniqueplayinNW Europe, producingh ydrocarbons onshoreThe Netherlands. Thispaperaims atacomprehensivedescription oftheserelatively unknown reservoirs andspeculatesonadditionalplaypotentialoutside ofthe current production areas. The MuschelkalkFormation consists ofpartially porous LowerandU pperMuschelkalkc arbonatess eparated byt ightMiddleM uschelkalk evaporites. The 100 mt hick LowerMuschelkalkh olds1 .9 BCM gasint he De Wijk Field.The reservoirisa limestone-dolomite-marl succession producingf rom severaldecimetrest hick calcisilitic dolo-mudstones encased intightlime-mudstones. The reservoirshows astratified architecturecomposed of16 cycleswiththinbut laterally continuous porous units. Goodreservoirquality faciesareconcentrated inthe upperthirdofthesecycles. Porositiesvary from 6to27%,(average 12%) andpermeabilitiesrange from 0.01 to 32 mD(average 0.06 mD). The reservoirr ocksr epresent innerr amp sediments ofastorm-dominated epeiric ramp. The 50m thick Upper Muschelkalkc ontains 0.8BCM gasint he CoevordenMuschelkalkF ield.The reservoirconsists ofseveral decimetrest hick peloidal-oolitic dolo-graint op ackstoneso fg oodpermeability interbedded withlower permeability dolo-mudstonest ow ackestones. Porosity variesfrom 5to 29% (average 15%) andpermeability rangesfrom 0.01 to 57mD(average 1mD). The permeabled olo-grainstoneso ccur chieflyaroundpeak transgression ande arly regression ofthe UpperMuschelkalk.The producingU pperMuschelkalkd eposits represent the innerramp section ofastorm-dominated homoclinalramp. Numerous gasshows inthe Lowerand UpperMuschelkalk, scattered overt he onshoreterritory ofT he Netherlands,suggest possiblemissed payand upside potential. The highest reservoirpotentialoccurs ingrainy dolomitic innerramp deposits. Thesearelikely to be located closeto the existingfi eldsint he NE Netherlands. Additionally,c urrently unrecognized potential couldbepresent ins outhern Germany andeastern Poland.

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