Ed Stockhausen knows the
strains, the pains and the gains that come from guiding
a drill bit through a zone with geosteering.
"First there is the 'landing the well in
the reservoir,' then there is the drilling of the lateral
section," he said. "It's kind of like landing a plane on
a runway in the fog, when the runway is moving up and down."
Officially, Stockhausen is a senior research
scientist at the Drilling Technology Center of Chevron Petroleum
Technology in Houston. More to the point, he serves as geosteering
advisor for Chevron operating units worldwide.
He defines geosteering simply as "the use
of real-time geological and directional data to help guide
or place a well."
So where does the pain come in?
Try geosteering the bit on a 1,000-foot lateral,
with a drill rate of 30 feet an hour, and you've been awake
for 24 hours assessing continuous downhole information,
with more than nine hours left to go.
Hello, coffee. Hello, mental overload.
Horizontal wells have become an important
production tool in the Middle East, according to Walid Kholeif,
operations geologist for Abu Dhabi Marine Operating Co.
(ADMA-OPCO). The company is 60 percent owned by Abu Dhabi
National Oil Co. (ADNOC) and 40 percent by minority partners,
An internal survey brought out requests for
information on well placement and steering, Kholeif recalled.
"The feedback was mainly directed toward
horizontal well activity," he said, "and, also, directed
toward the drilling techniques instead of the geology."
In response, AAPG helped arrange and sponsored
the Abu Dhabi Geosteering Workshop, which was held in April.
Kholeif coordinated the workshop and called it "perfect"
for the company's needs.
"It was really practical information," he
noted, "not just academic, or only a few papers you could
Thinking in a Real (Time) Way
Geosteering involves "a different kind of
thinking from what a geologist normally gets into," Stockhausen
said. "We're used to taking weeks and months to think about
the data and adjust our maps."
In geosteering, the geologist gets real-time
data from downhole tools and gives the driller feedback
to direct the bit.
"You're trying to predict the geology just
ahead of the bit, particularly the dip of the beds," Stockhausen
said. "You're making decisions on the spot, continuously,
and you do the best you can.
"Many times you get lost in these wells,"
he continued. "You don't know if you're going out the top
of the zone, or the bottom of the zone. You're looking for
a marker bed."
Some horizontal laterals may drill at a rate
of only 15 feet per hour, and Stockhausen described those
wells as "cruel, because you're getting data so slowly,
there is too much time for second-guessing yourself."
Other 1,500-2,000-foot laterals may drill
in less than a day.
"Those wells are actually a blessing," he
explained, "because you can say, 'OK, this is going to take
15 hours and I can stay awake, I will make my decisions
and it will be over soon.'"
Is it possible to use two geologists taking
turns on a longer project? Sure, Stockhausen said - but
then you run into the traditional problem: Whenever you
have two geologists, you get three interpretations.
In Abu Dhabi, according to Kholeif, geosteering
helps to place wells - or "land" wells - in the reservoir
layer to facilitate water or gas injection. It's a useful
tool in efforts to maintain reservoir pressure.
"We have not yet done this for exploration,"
he said. "It's strictly for production."
The typical geosteering project begins with
well planning, and in particular a drilling model that includes
geology, resistivity and other important reservoir elements,
according to Kholeif. And a good project places the geologist
at the drill site "to direct the well to the best reservoir
"There should be some experience in the field,"
Kholeif said. "If you have a geologist who is not experienced
in the region, it would be a little difficult for him to
"The key to the success of geosteering is
really in the preplanning stage. You're trying to plan around
Usually, Stockhausen said, "your targets
are smaller than the accuracy of your maps.
"You try to use marker zones that are above
the beds you're trying to get into," he continued. "You
plan the design around those marker beds and make sure you
enter them at the angle you want. This allows you to then
continue forward to softly land the well in the reservoir.
"Getting too far ahead or behind on the plan
leads to lost footage in the lateral section and lost reserves."
Stockhausen jokingly added that "you aren't
allowed to have any of those unanticipated (geologic) faults
along the well path. Little 10-foot faults can throw everything
out the door."
He admits that geosteering initially earned
a bad name for being too expensive - but, he added, geosteering
actually involves a comparison of costs and benefits.
For instance, tools that provide inclinational
measurement near the bit cost more to use than tools with
these instruments further back, Stockhausen explained. The
difference may be a three-foot drilling window from near-bit
readings compared to a 10-foot window from other tools.
If the smaller drilling window leads to more
accurate well placement, and the difference is capturing
100,000 more barrels of oil, the cost of near-bit information,
he said, may be well justified.
Displays of downhole information in geosteering
would be familiar to most geologists. Data is sent uphole
and displayed in the normal way, said Ted Bornemann, principal
geologist for Schlumberger's Center for Advanced Formation
Evaluation in Houston - better known as the "SCAFE" (and
pronounced as "S-Café").
"The commonly used tools are the gamma ray
tools and the resistivity tools," he said. "Some new technology
that's emerging now is the use of image data while drilling
- real-time imaging."
Those imaging tools "show very graphically
whether we are drilling up or down, or staying within the
layer of the reservoir," said Bornemann, who specializes
in forward modeling in drilling.
Imaging tools are located some 35 feet behind
the bit, he said, while gamma ray and resistivity tools
can be located right behind the bit. In every case, data
is transmitted uphole by mud telemetry - pulses sent through
"That's why the data transmission is somewhat
limited," he said. "It's not the bandwidth and the signal
type you have in a wire, like you can get with wireline
What might not be familiar to geologists
are the downhole readings from a lateral well. Resistivity
anisotropy produces anomously high resistivity readings
different from those seen in a vertical well, according
"In essence, the resistivity measurements
look a little unusual," he said.
Where Am I?
Geologists who want to be successful in geosteering
need to learn a foreign language:
"Drillers want target information," Stockhausen
said. "This is one of the biggest challenges, how to communicate
to the driller.
"I like to have the geologist on the rig
site, because they can talk to the driller in person and
To help guide the well, a geologist should
know how the driller targets the hole and what information
is needed to make adjustments. It's also important to understand
the basics of directional drilling, Stockhausen said. Ask
a driller if it's possible to lower the hole 10 feet in
the next 10 feet of forward drilling, and the always-polite
driller will respond:
"I don't believe so, sir."
Or words to that effect.
"Targets in horizontal wells tend to be lines
- actually, moving lines - and well plans need to be flexible,"
"As we get information on the geology, we
may have to admit that our line's in the wrong place and
ask if we can please move it. But if you make too many kinks
in the well you're going to stick the drill pipe," Stockhausen
And the geologist has to exercise restraint
in making adjustments as downhole geology and measurement
differ from the predrill model.
It's easy to oversteer a hole.
"There's always a constant issue of losing
the well," Stockhausen said. "I try to preplan my decision
points around a few key marker beds: These decision points
should be communicated to the entire drilling team prior
"When these beds are encountered while drilling,
then it is time to make a decision - and then I'm going
to talk to the driller about how to adjust the well path,"
"Preplanning key geosteering decision points
allows wells to be drilled without as much alarm."
"Also, you've got to do everything in a very
site-specific way," he continued. "That's one of my favorite
terms, site-specific. You can't use the same geosteering
techniques for every well in the world."
"Drilling a well is not like playing with
a joystick on the computer," Bornemann noted. "There are
a lot of restrictions on drilling a well."
In geosteering, the geologist must "work
out the geology as detailed as possible along the planned
azimuth of the well," he said, while knowing the characteristics
of each layer above and below the hole.
"The real trick in geosteering is to know
where you are geologically," Bornemann continued. "Through
this whole process of landing the well, we will encounter
a number of these formation tops. If we can recognize this
marker on this new well we are drilling, we can say, 'Now
we know where we are.'
"That does not mean we know in absolute depth
from the surface where we are, but we know that 15 feet
below this marker we have identified is our target zone."
Awareness and Accuracy
Even with good knowledge and reliable measurements,
location can be difficult to pin down. That's when the driller
is waiting for instructions and instead of breaking out
in a smile, the geologist breaks out in a sweat.
"Everyone on the rig knows if the geologist
is lost," Bornemann said.
"The people who tried to do horizontal well
drilling without geosteering techniques drilled to a line
drawn on a sheet of paper. You'd give a piece of paper to
a driller and say, 'Drill these XYZ coordinates' without
putting any geology on there," Stockhausen said.
The problem with that approach, Bornemann
noted, is that a good driller could drill a perfect hole
that matched the coordinates exactly, and the well might
not be in the reservoir. There's too much uncertainty in
Stockhausen recalled his frustration the
first time he tried geosteering, not having the tools and
techniques he needed. He said Chevron recognized the need
for a company-wide approach to geosteering instruction.
"In team environments, geologists become
severely isolated from other geologists. We were all making
the same kind of mistakes," he said. "That's when we began
to see that there was some teaching needed."
Because of their reputations and experience,
Stockhausen and Bornemann were asked to conduct the Abu
Dhabi Geosteering Workshop. One challenge in Abu Dhabi,
Stockhausen said, is to keep a directionally drilled hole
in a thin, high-porosity zone for as much as 2,000 or 3,000
"You can imagine trying to stay in a 10-foot
zone for 2,000-3,000 feet, how accurate you have to be.
Some of this sounds somewhat impossible, but the zone helps
you. A lot of times, the zone you're drilling in is the
softest zone, and the bit is very content to stay there,"
Bornemann said he might have changed a few
things about the workshop held in April, but not very much.
He rated it highly successful for a first-of-its-kind effort.
"One of the biggest things was that everybody
in the class came away with the feeling that he was well
aware of the problematics of geosteering," he said, "and
that is, principally, that you have to be aware of the uncertainties
involved and what you can do to minimize them, thus drilling
a successful horizontal well."