Production from Muschelkalk carbonates (Triassic, NE Netherlands) - Unique play or overlooked opportunity?
2020-04-30T14:14:46Z (GMT) by
producing hydrocarbons onshore the Netherlands. This paper aims at comprehensively describing these relatively unknown reservoirs and speculating on additional play potential outside of the current production areas. The Muschelkalk formation consists of partially porous Lower and Upper Muschelkalk carbonates separated by tight Middle Muschelkalk evaporites. The 100 meter thick Lower Muschelkalk holds 1.9 bcm gas in the De Wijk field. The reservoir is a limestone-dolomite-marl succession producing from several decimetres thick calcisilitic dolo-mudstones encased in tight lime-mudstones. The reservoir shows a layer-cake-type architecture composed of sixteen cycles with thin, but laterally continuous porous units. Good reservoir facies is concentrated in the upper third of these cycles. Porosities vary from 6 to 27%, (average of 12%) and permeabilities range from 0.01 to 32 mD (average 0.06 mD). The reservoir rocks represent inner ramp sediments of a storm-dominated epeiric ramp. The 50 metres thick Upper Muschelkalk contains 0.8 bcm gas in the Coevorden Muschelkalk field. The reservoir consists of decimeters thick peloidal-oolitic dolo-grain- to packstones of good permeability interbedded with lower permeable dolo-mudstones to wackestones. Porosity varies from 5 to 29% (average 15%) and permeability ranges from 0.01 to 57 mD (av. 1 mD). The permeable dolo-grainstones occur chiefly around peak transgression and early regression of the Upper Muschelkalk. The producing Upper Muschelkalk deposits represent the inner ramp section of a storm-dominated homoclinal ramp. Numerous gas shows in the Lower and Upper Muschelkalk, scattered over the onshore territory of the Netherlands, suggest missed-pay and possible upside potential. The highest reservoir potential occurs in grainy dolomitic inner ramp deposits. In Holland these are likely located close to the existing fields. Additional, currently unrecognized potential could be present in Southern Germany and Eastern Poland.