exploration review THE BAKKEN AT ANTLER AND SINCLAIR

EXPLORATION REVIEW
However, Burrus et al have observed that though most oil
generated in Bakken source rocks has been expelled from
Bakken shales, there are few Bakken-sourced accumulations
in the Early Mississippian Madison Group. They explain
that much of the expelled oil may remain dispersed (and
immobile) in the vast volume of the Madison (post-Bakken)
carbonates. They also observe that oil generation causes Bakken
overpressure, which provides a mechanism for Bakken oil
to migrate both vertically and laterally. The overpressured
zone is highlighted on the Bakken Members subcrop map
( top page B32). The energy of the overpressure zone,
which may allow Bakken oil to migrate far updip northwards
beyond the oil window through the Bakken Middle Member
(Burrus et al 1996), possibly explains the occurrence of
Bakken and Torquay oil in Manitoba.
Detailed examination of Bakken cores, geophysical logs,
and production data in southeastern Saskatchewan indicates
that significant potential exists for bypassed pay and the
opportunity to find additional oil in siltstones and sandstones
of the Middle Member of the Bakken Formation. Weathered
and brecciated dolostones of the Torquay Formation in
southeastern Saskatchewan and southwestern Manitoba
also exhibit high and relatively untested potential for oil
production. The relatively low permeability of these rocks
suggests that they might best be developed using horizontal
drilling and completion programs. A large untested and
poorly evaluated rock volume remains in the Bakken and
Torquay formations of southeastern Saskatchewan, within
which there may be significant potential for finding new oil.
(Kreis, Costa and Osadetz, 2005) Recent drilling success
by Tundra Oil and Gas and others in the Sinclair Field
dramatically illustrates that this also applies to southwestern
Manitoba.
First Bakken production from Manitoba began in the Daly
Field, in October 1985, when Newscope Resources tied in
Tundra Kola Unit No.1 13-21-10-29 W1. That well, a New
Field Wildcat rig released on October 1, 1985 was drilled to
a total depth of 905m in the Torquay. It came on stream at
an initial rate of 73 bopd, and produced a little over 73,400
barrels of oil until September 1992, when it was converted
to a water injection well.
The main Bakken fields in Manitoba are the Daly Field,
in which oil is produced from sweet spots in an area of
ubiquitous oil saturation, the Birdtail Field, which involves
structural and stratigraphic closures in a regionally wet
sand, and the recently discovered Sinclair Field, which
produces from a flow unit (a rock volume with identifiable
fluid flow characteristics that can be modeled) comprising
both the Middle Bakken Member, and the Upper Devonian
Torquay Formation, below the sub-Bakken unconformity.
(Barchyn, 2005)
The Daly Field began with the discovery of a major Lodgepole
pool in 1950. The Bakken is oil-charged throughout the area
with 40° API oil, and production performance is determined
by reservoir quality in the Middle Bakken Member sandstone.
“Sweet Spots” trend north-south, parallel to depositional
strike, the best pools are under waterflood, and Bakken
production is commonly commingled with the overlying
Lodgepole. A log suite ( top opposite page) depicts a
Middle Bakken sand with an average porosity of 17%,
an average permeability of 12.0md and a net pay of 5.0m
(Barchyn, 2005).
In the Birdtail Field, the Bakken produces 36° API oil from
small reservoirs (in the order of one half million barrels).
These accumulations are usually encountered at depths of
about 520m and are conventionally trapped in good quality
Middle Bakken sand bodies with identifiable downdip water
legs. Trapping appears to be a combination of structural and
stratigraphic factors. The pools are mostly under waterflood.
A Birdtail Field log suite ( bottom opposite page) shows
a Middle Bakken reservoir with an average porosity of 18%,
and a net pay of 3.5m (Barchyn, 2005).
The newly discovered (2003) Sinclair Field is still under
active development. The flow unit (reservoir) straddles
the sub-Bakken unconformity with some pay from the
Middle Bakken Member, but the bulk of pay found in
the underlying sandy dolomite of the Torquay Formation.
Log expressions are subtle and do not necessarily explain
variations in productivity A Sinclair Field log suite
( page B36) depicts a Torquay reservoir with an average
porosity of 16%, an average permeability of 3.5md and a
net pay of 6.0m. (Barchyn, 2005)
B34 VOLUME 5 2006 CANADIAN DISCOVERY DIGEST