Diagenesis and Structural
Control on Production from
Devonian Duperow Formation, Tree Top Field, Billings Anticline, North Dakota
Randolph B. Burke, Tom J. Heck
The Billings anticline is a north-plunging structure in the Williston basin
of west-central North Dakota that is covered by most of the Phanerozoic section.
Structure and isopach maps
of the Duperow Formation suggest that the structure
is fault bounded on the east side and apparently crossed by a series of
northeast-southwest-trending fractures. Tree Top field is located on the eastern
side of the structure. Hydrocarbons are produced from rocks of three different
ages in more than four zones, including the Duperow Formation. Tree Top field is
one of six fields on the anticline producing from the Duperow Formation.
Tree Top field has produced over 350,000 bbl of Duperow oil since its
discovery in 1979. Essentially, one well has produced 84% of this oil. The well
is located proximal to the junction of the east-bounding fault and one of the
apparent cross
fractures.
Maps
of porosity and lithology of the producing zone
show lateral porosity pinch-out coincident with lithologic changes from dolomite
to limestone.
The Duperow Formation consists of numerous complete and incomplete, shallow-water deposition, sediment packages. The producing zone in Tree Top field is in the heavily dolomitized subbank and perilittoral zones of cycle 3.
Core analyses show that the dominant type of porosity in the dolomite is
intercrystalline and is enhanced by molds and microvugs. Intercrystalline
porosity is being altered by replacement and infilling by anhydrite and calcite.
Core analyses, in conjunction with lithologic, porosity, structure, and isopach
maps
of the pay zone, suggest that the preservation and enhancement of dolomite
porosity may be most effective proximal to fracture zones.
AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988