Exploration Frontiers in the Bakken Formation, Montana and North Dakota
LeFever, Julie A.
North Dakota Geological Survey, Grand
Forks, ND
Early exploration provides the framework for the current Bakken
play. Numerous studies assessed optimum shale thickness, TOC, and
wireline log resistivity relationship to thermal maturation. Maps were
constructed showing the aerial distribution of the onset of
hydrocarbon generation and areas of intense hydrocarbon generation
in the Upper and Lower Bakken shales. Results show the shales range
from 28 to 55 ft and are predominantly illite (up to 42%), organic
material, silt-and clay-sized quartz, calcite, feldspar, and pyrite. No
discernable trends in the major and heavy element geochemistry are
observed. TOCs of up to 30% suggests large in place reserves remain
ranging from 200 to 415 billion barrels. Bakken exploration has relied
heavily on available technology. Formation damage was minimized
using slightly under-balanced inverted mud systems. Vertical wells
were fracture stimulated, whereas horizontal wells relied on naturally
occurring fractures. Horizontal wells in the Upper Bakken Shale wells
met with moderate success as the combination of low oil price,
improper spacing, and poor EUR's ended the first phase of horizontal
Bakken exploration.
Current horizontal wells target the middle member, consisting of
a sequence of low porosity, low permeability dolomite, silty dolomite,
sandstone, and shale. Wells in the silty dolomite facies in Elm Coulee
Field, Montana averaged 500,000 BOPW. The average pay thickness
is 10 ft. To date, North Dakota well results are highly variable as
drilling and completion practices adjust to account for lithologic
variability in the Middle Bakken Member.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah