Too often the public perception of the
petroleum industry may be that of a fiefdom ruled by the major oil
companies whose executives sit in some secret room and control the
energy resources of the world.
OK, we all know that's ridiculous.
But while majors command the lion's share of worldwide
production, sometimes it's the little independent shops that --
through creative thinking -- can advance the science of geology
and conceive new ideas about petroleum systems around the world.
Independent geologists working in small offices all
over the United States still approach their science the old fashioned
way: They earn it, and through years of experience they conceive
new ideas about old problems, and with hands-on, detailed study
of existing data develop new play concepts for explorationists to
test.
That's just what one Crawford, Colo.-based independent
geologist has done in the Williston Basin.
W. Richard Moore applied his 30 years of experience
in the Rocky Mountain region to a puzzle that has baffled the industry
for years, And he just may have a solution.
"Major producing trends in the Williston Basin terminate
for no apparent reason," Moore said.
The basin's northeast part in Canada is extremely
prolific with about four billion barrels of recoverable oil -- fairly
well outlined production areas. But as those Mississippian and Ordovician
producing trends enter North Dakota the number of fields decreases
dramatically.
"The Mississippian trend that accounts for much of
the oil in Canada stops rather abruptly as it enters the United
States," Moore explained, "and there's never been a good explanation
for why it stops."
This leaves much of the southern and eastern portions
of the basin with little production.
Analyzing
the Data
To better understand what controls the producing
trends and, therefore, have a model that can be used to develop
new trends, Moore collected and analyzed several data sets, including
Bouguer gravity, geothermal gradients and surface linear patterns.
"I was working at developing prospects, and initially
I was doing a study of the Niobrara formation in the Denver Basin,"
Moore said. "I became intrigued by what I was seeing in the geothermal
gradient, so I went back and started looking at areas of high geothermal
gradient and negative gravity anomalies and saw there was a correlation
between the two.
"I love looking at all different kinds of maps, and
I saw a hint," he continued. "This is one of those happenstances
where you suddenly see a correlation and set out to understand it."
All of these data are readily available, Moore said.
Both Bouguer gravity and surface linear information are accessible
in published literature and he made geothermal gradient maps based
on temperature readings in area well log data.
"You don't need a lot of high quality seismic data
to get a basic outline for some new play areas," he said. "You can
assimilate this type of existing information and get a good first
look at a region."
Analysis of the data sets in the Williston Basin
showed a strong correlation between areas of hydrocarbon production,
high geothermal gradient, high intensity of surface linears and
negative Bouguer gravity anomalies.
Based on his study Moore believes that these areas
of strong correlation reflect high fracture intensity in the basement
and overlying sedimentary sequences and that these fracture systems
control trap formation and hydrocarbon migration.
"As you come south of the known trends, hydrocarbon
production stops because the basement fracture systems terminate,"
he said. "You can see on the data sets that lower geothermal gradient,
positive Bouguer gravity and a lower intensity of surface linears
characterize these non-productive regions."
While there are no definite answers to why the fracture
systems terminate, Moore said it's likely related to basement lithology
or basement tectonics down in the Earth's mantle or crust.
"If you look at the surface of the earth, there are
areas that are highly fractured and areas that aren't, and we really
don't fully understand why you have fractures in one area and not
in others," he said. "But basement lithology and tectonics are the
likely determining factors."
Signs of Potential
Based on his study, Moore believes he has identified
some potentially prospective areas in the Williston Basin and other
Rocky Mountain basins as well.
"I found in the southeastern portion of the basin
these areas of high geothermal gradient, Bouguer gravity minimums,
and high surface linears are duplicated," he said. "I think a large
area of over 3,000 square miles in the southern Williston Basin
can be shown to be highly prospective in several Paleozoic horizons."
Significant production offsets the potential area,
and hydrocarbon shows exist in the few wells that have been drilled
in the area, he added.
This prospective area is east of the producing regions
of the Williston and west of Bismarck in Morton and Grant counties
of North Dakota. Along the edge of this area of concentration of
geothermal gradient, surface linears and Bouguer gravity minimums
there are three significant fields that produce from the Ordovician
Red River or the Cambro-Ordovician Winnipeg formations.
"In my mind this is another area with significant
basement fracturing that should have traps primarily in the Ordovician
and the Winnipeg," he said.
Buffalo Creek, a one-well field that produces from
the Red River, has pumped about 600,000 barrels of oil since the
mid-1970s. The Taylor and Richardton fields were discovered in the
late 1970s to early 1980s, and both produce from the Winnipeg.
- The Taylor Field has produced about six billion cubic feet
of natural gas with ultimate recoverable reserves of around 10
billion cubic feet from one well.
- The Richardton Field has made about three billion cubic feet
of gas.
There also have been some significant shows in this
prospective area from the same zones that produce at Buffalo Creek,
Taylor and Richardton.
"These shows are important -- they are a strong indicator
that the region has potential," Moore said. "There have only been
10 wells drilled in this 3,000-square-mile area, and five of those
wells had significant shows of gas from the Winnipeg."
Risky Business
Natural gas was not an exploration focus for the
majority of operators when these wells were drilled, and the producing
formations are found at 10,000 feet, making the wells relatively
expensive to drill.
Of course, that's all changed. Today a growing list
of companies are actively searching for new natural gas plays, and
substantially higher natural gas prices are expanding the economic
limits of exploration opportunities.
"This combination of factors could certainly heighten
interest in this area and (perhaps) prompt some companies to test
the region," Moore said. "It's a matter of someone willing to jump
in and take the risk."
Individual wells have the potential to make a minimum
of 10 billion cubic feet of gas or upwards of one million barrels
of oil, Moore believes.
"Plus, this is a complex play that will require multi-well
programs to tap the subtle structures in the regions," he added.
"This is a huge area that's virtually untapped, but could potentially
yield trillions of cubic feet of natural gas."
Moore is conducting this same type of study on other
Rocky Mountain basins.
"We see large non-productive areas right next to
highly productive regions all over the Rocky Mountains," he said.
"The conventional explanation has always been a lack of exploration.
However, today I think more people are recognizing that we must
look at basement tectonics and its control on producing trends."
Identifying these potentially productive regions
based on geothermal gradient, Bouguer gravity and surface linears
is an ongoing project for Moore.
"I think the same type of basement tectonics I saw
in the Williston Basin controls almost all of the hydrocarbon systems
in the Rockies," he said, "and by mapping these areas of high fractures
we can better understand old producing trends and explore for new
trends.
"This is not confined to the Rockies either," he
added. "Many of the eastern U.S. basins share these same characteristics,
including the Michigan Basin, the Illinois Basin and the Appalachian
Basin."