Doug N. Harvey1,
Don M. Kent2,
Hairuo Qing3
(1) University of Regina, S4S 0A2 Regina, SK
(2) University of Regina, Regina, SK
(3) University of Regina
Abstract: Characterization
of Mississippian Midale and Ratcliffe
Reservoir
Dolostones of Southeast Saskatchewan
Petrography, diagenesis, and
reservoir
characteristics of dolomite reservoirs were studied from
Mississippian
carbonates
of the northern Williston Basin in southeastern
Saskatchewan. These dolomites are hosted in the Midale and Ratcliffe Beds and
were sampled from the Benson Midale, Glen Ewen Midale, Oungre Ratcliffe, and
Hummingbird Ratcliffe fields. The Midale and Ratcliffe are part of the Madison
Group which represents shallowing upward cycles deposited in an epeiric sea. It
consists of deeper water
carbonates
at the base and shallow marine
carbonates
and tidal flat
carbonates
and evaporites in the upper portions. Dolomites in
the Midale and Ratcliffe dolomites represent the dolomitization of lime muds
deposited in restricted lagoonal to subtidal-intertidal environments.
Petrographically and
petrophysically, two types of dolomites are recognized in these beds. Type 1 is
cryptocrystalline (<4 µm) to microcrystalline (4-8 µm) dolomites associated
with tidal flat sediments and evaporitic anhydrites. These dolomites generally
have low porosity and permeability and occur in sections both above and below
the current producing reservoirs. These dolomites are interpreted to have
formed penecontemporaneously by evaporitic sea water. Type 2 is
microcrystalline to microsucrosic (8-14 µm) reservoir
dolomites with good intercrystalline
porosity (~21%) and permeability (~12 md). The
reservoir
dolomites are found in
all four fields and their effectiveness as reservoirs appears to depend on
degree of dolomitization. Geochemical analysis will be carried out to determine
the source and timing of fluids associated with the
reservoir
quality
dolomites.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana