E&P MOMENTUM

Bakken continue to mount. Production

has spread from the play’s genesis

in Richland County, Montana, into

McKenzie, Golden Valley and Billings

counties, North Dakota. The horizontal

Bakken play, discovered in 2000, now

holds the potential to significantly

contribute to the nation’s oil reserves,

according to a recent report by the U.S.

Energy Information Administration.

The report, by the EIA’s office of oil

and gas, reserves and production division,

is the first in a series about technology-

based oil and gas plays.

The Bakken is very much a technology

story. Horizontal drilling and completion

techniques, especially horizontal wellbore

stimulations, have wedged open this play.

Elm Coulee Field, in Richland County,

ranks as the largest discovery to date. In

2005, Elm Coulee produced 15 million barrels

of oil from the middle member of the

Bakken formation, nearly half of Montana’s

total daily crude production.

And it appears that considerably more oil

can be produced. Headington Oil Co., a

main operator in the field, has estimated it

contains in-place resources of 5 million barrels

per square mile. At an assumed recovery

of 10%, Elm Coulee could produce an

astonishing 500 million barrels.

Meanwhile, the U.S. Geological Survey

estimates potential oil in place in the overall

Bakken play is between 271- and 502 billion

barrels of oil, according to a recent study.

That’s a gigantic leap from estimates the

USGS made in 1995, when it calculated that

only 151 million barrels were technically recoverable

from the Bakken.

“If the potential bears out, this could (depending

on recovery factors) increase the estimate

of technically recoverable crude oil

resources in the United States by billions of

barrels,” the EIA reports. At present, the

USGS estimate for all technically recoverable

oil resources in the country, not including

the Bakken, is 175 billion barrels.

The Bakken was deposited during the

Upper Devonian and Lower Mississippian

periods. An upper shale that is 23 feet thick

and a 50-foot lower shale sandwich a middle

member composed of interbedded limestones,

dolomites, siltstones and sandstones.

Current drilling targets this middle member,

some 85 feet thick.

The Bakken formation is prolific because

it is tightly sealed by overlying and underlying

carbonates. As hydrocarbons were generated

in the Bakken shales during geologic

time, internal fluid pressures fractured the

rocks. The bounds of the thermally mature

portion of the Bakken are drawn at depths of

8,500 feet or greater, which corresponds to

temperatures of 100° Celsius or above. Inside

that area, the Bakken is overpressured,

often oil-wet, and rife with natural fractures

that make it capable of producing at high

rates.

Of course, oil has been produced from the

Bakken for decades. But earlier operators

were often frustrated. Vertical wells attempted

to intersect natural fracture systems.

But Bakken shales are highly reactive to

water, and older-style drilling and completion

fluids caused swelling that reduced or

eliminated permeabilities. Furthermore, the

Bakken contains iron pyrite, which reacts

with hydrochloric acid to form a precipitate

that also damaged formations. And, because

the Bakken is overpressured, normal sand

proppants were crushed at the pressures required

for stimulations.

Today, producers drill long horizontal laterals

and routinely fracture-stimulate, and

achieve excellent results. Wellbores are

aligned so that induced fractures are oriented

longitudinally. The stimulations use

crush-resistant proppants and are produced

through uncemented perforated liners.

Indeed, so much oil is being discovered

and produced from the play that the Williston

Basin’s pipeline system—which also

moves Canadian oil—is full. Producers have

suffered discounts because of competition

for pipeline space, and some have announced

production shut-ins and drilling

postponement. Consequently, midstream

companies are stepping into the area.

Perhaps the most remarkable aspect of the

Bakken is its provenance in a vintage

petroleum basin. This play was realized because

of the stick-to-it attitude of independent

companies that pioneered it.

“Success came from analysis of geologic

data on a decades-old producing area, identification

of untapped resources, and application

of the new drilling and completion

technology necessary to exploit them,” the

EIA reports.

Success stories in the horizontal

love those indies rosy!

wildcatters of yore!