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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The Mission Canyon is interpreted to be a regressive shoaling-upward, carbonate to anhydrite sequence deposited by a shallow epeiric sea. Upsection most of the formation is of subtidal origin, deposited as: (1) basinal "deeper water" carbonates, below wave base; (2) open shallow marine, which deposited major carbonate cycles of mudstone grading into skeletal packstone/grainstone; (3) transitional open to restricted marine, with minor carbonate cycles of mudstone grading into skeletal wackestone; (4) restricted marine of pelletal wackestone/packstone; and (5) narrow marginal, nearshore marine of skeletal wackestone interbedded with emergent intertidal deposits of skeletal, ooid-pisolitic packstone. Cratonward, the intertidal is interbedded with lagoonal limestones and both overlain by tidal flat to supratidal anhydrite beds.
The reservoir is structurally trapped within a northward-plunging anticlinal nose with less than 100 ft (30 m) of closure. Facies changes create stratigraphic entrapment southward. The seal is the overlying anhydrite beds.
Porous hydrocarbon-bearing beds are isolated within transitional open to restricted marine, restricted marine, and marginal nearshore marine facies. These lime-mud-rich beds underwent replacement by anhydrite to skeletal fragments, which was later leached, and the muddy matrix was dolomitzed to a porous calcareous dolostone.
Thin-section petrography and scanning electron microscopy studies of core samples and relief pore casts reveal four pore types. Pore types include moldic pores and dolomite intercrystal pores; namely, polyhedral, tetrahedral and interboundary-sheet pores, each pore progressively smaller in size. Pore throats are of two major sizes, the largest five times the width of the smallest.
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