Instructor Bailey Bubach
PTRE – 493 Shale plays
February 1, 2018
Williston basin Bakken Formation.
The Williston Basin is an elliptical shaped
depression, that include the Bakken shale and underlying Three Forks formation.
It is known for its rich deposits of petroleum and potash. United States
portion of the Williston basin continuous from North Dakota to South Dakota and
parts of Montana and Wyoming with approximately one hundred forty square miles.
Oil first was discovered in Williston basin along the Cedar Creek anticline in
southeastern Montana in 1920s. Later, after year of exploring, testing, mapping,
and drilling it was discovered as one of the largest oil and gas reserve in
United states of America.
Bakken formation is composed of three main
members, which is lower member, middle member and upper member. Also, there is
a nine different lithofacies that contains in Bakken formation. Eight of them
in the middle member and the only one is occurred in upper and lower members is
facies Mb, which is organic rich black mudstone. For the lower Bakken member
accumulation of laminated, fine grained, organic rich mud (Lithofacies Mb)
occurred in deep water marine, usually take place when sea level rise. The
middle Bakken member, which is composed of eight gray mudstones and sandstones
lithofacies. It has a maximum thickens of ninety-eight feet in west- central
Saskatchewan. The middle member is sub-divided into three parts, sub- unit-A
the basal mudstone, sub-unit-B middle sandstone and mudstone and sub- unit C is
upper mudstone. These sub-units are located throughout the inner of the
Williston Basin where each has maximum thickness near center and thin to zero
near the basin margin. Lastly, is upper member which is black mudstone that is
very similar to the lower member. The lower and upped members contain different
attentiveness such as feldspar, quartz, illite, dolomite, calcite, pyrite and
high concentration of organic matter.
Composition of Mb facies contain black clays,
silt, quartz silt grain, and amorphous organic materials. Also, it classified
as primary structure and secondary structures. Similarly, for the middle member
that contain eight lithofacies such as St, Sr, Sf, Sw, MSI, Msh, Msm, and Lo. All
of them has a different structures and compositions. All the information of
this basin can be obtained from core examination, well logs, seismic and
Williston Basin has six major depositional
sequences which goes from oldest to the youngest, the Sauk, Tippecanoe,
Kaskaskia, Absaroka, Zuni and Tejas. These sequences occur in the different
geological time scale. For example, the evolution of Willison basin started
with the Sauk which is sequence of sedimentary rocks and deadwood formation in
the late Cambrian and early Ordovician age. Then, Tippecanoe sedimentation took
place in Ordovician and Silurian time zone. After that, deposition of lower Kaskaskia
occurred in Devonian and upper Kaskaskia in Mississippian age, which created a marine
connection and disconnection in the different sides of basin. Later, Absaroka
Sequence took over which created clastic sedimentary as a main element and mix
of evaporites and some carbonates. Finally, Tejas sequence which took place in
Tertiary, Quaternary and Holocene age. In addition, these major sequences are
classifying as different orders; first, second are most likely result from
eustatic changes in sea level. As well as third, and fourth order could result
from tectonic activities or both eustasy and tectonics.
Furthermore, Williston Basin has two different
energy resources beside the hydrocarbon which is Potash that is produced from
the Williston Basin which makes Canada the worlds leading producer of that
commodity. Also, Williston Basin holds large coal deposits, primarily in the Fort
Union Formation in the Paleogene age.
In conclusion, oil and gas production been expanding
very quickly in the Williston Basin. The Bakken boom has pushed North Dakota
into the top ranks of oil- producing states with the help of advanced hydraulic
fracturing and modern horizontal drilling technologies. Therefore, fracking has
unlocked huge U.S shale reserve, increasing in tremendous amount of oil and gas
production and creating millions of jobs that promote economic growth.