The bug man cometh.
No, we're not talking about insect exterminators,
nor electronic "bugging" devices, nor coughs and sneezes, nor people
who are a real pain to have around.
We're talking about creepy, crawly bugs — you know,
the very essence of hydrocarbons.
Why? Because today, more than ever, bugs are aiding
in the exploration and production of oil and gas.
Except today, the "bug men" have left their white
coats back in the laboratory and are working in the field alongside
geologists, engineers and drilling teams to help maximize production
and minimize costs.
Of all recent developments in the role of production
biostratigraphy, none has had a more immediate and perceptible impact
than biosteering, according to Simon Payne, biostrat network co-leader
for BP in Aberdeen, Scotland.
Few companies have pursued this technology as enthusiastically
as BP — to date the company has used biosteering on more than 200
wells in 20 fields worldwide, primarily in northwest Europe — and
Payne is hopeful that the firm's efforts will prove the worth of
biosteering to the global industry.
Payne, along with several colleagues from BP, submitted
a paper titled "The Role and Value of Biosteering in Hydrocarbon
Reservoir Exploitation" at the recent AAPG International Meeting
in Cairo, Egypt. The paper was part of a session on advances in
Driven by the need for reservoir-scale stratigraphic
control to help say "where we are" during the drilling of high-angle
and horizontal wells, biosteering has rapidly become an integral,
cost-effective part of the geosteering toolkit, he said.
"We think the technology has added tens of thousands
of barrels of oil a day to BP-operated global production," Payne
said. "Today this is a fundamental tool for the company.
"We still have to sell partners on the technique,"
he added, "but we find that it only takes a bit of misfortune on
one well where the 'bug men' save the day to make converts of the
Knowing Where You Are
The tool, according to Payne, ties together several
aspects of the subsurface spectrum:
- Reservoir geology.
To begin the process, a precise stratigraphic layering
of the field is undertaken. Production biostratigraphy aims to subdivide
the reservoir into unique, correlatable time-slices using field-specific
microfossil bioevents to "fingerprint" individual layers.
Layering the reservoir at a higher resolution than
regional, exploration-scale biostratigraphy, typically provides
greater precision than seismic — and greater dimension than log
or lithological analysis. This enables heterogeneity to be better
understood, and gives a notional idea of which packages may be connected.
Critically, it also sets up the anticipated sequence
of high-resolution bioevents for use in biosteering.
"In a clastic package the fossil-bearing rocks are
generally the muds and silts that envelop and subdivide the pay,"
Payne said. "In a carbonate setting the whole interval is often
Biosteering entails making the reservoir defining
bioevent calls at rig site while drilling, allowing a real-time
monitoring of well path relative to the reservoir.
"With this technique, reservoir penetration can be
maximized," Payne said. "By discriminating between non-pay above,
below and within the reservoir we can help explain unpredicted exits,
for example, drilling out of the top or floor of the target or across
sub-seismic scale faults.
"Biosteering helps guide well trajectory back into
reservoir — drill up or drill down — boosting access to reserves,"
he added. "It is an addition to the geosteering armory, but a very
handy one at that."
It also can help cut costs by optimizing casing and
TD calls, giving the assurance that all targets have been penetrated.
"And above the target, well-angle build can be calibrated
to optimize reservoir entry by an ongoing comparison with offset
data," he said, "telling us if horizons are coming in deep or shallow,
thereby helping to predict proximity to top reservoir."
A typical daily wellsite cost for all of this is
about $1,500; a precursor high resolution reservoir layering study
may be of the order of a few tens of thousands of dollars.
Biosteering is really "a happy combination of three
things," he said:
- The technology to drill high-angle wells.
- The drive to define biostratigraphy at the well.
- The application of biostrat at reservoir scale.
"In many people's minds biostrat is an exploration
scale tool," he said, "but with this technology we can step beyond
that application to a higher resolution and map the reservoir."
A Simple Science
BP has aggressively pursued the biosteering technique
since 1995, when the tool was first applied at the Donan Field in
the UK North Sea.
"The plan on Donan was to try and stay in the upper
most reservoir package and have some control in terms of layering
while drilling," Payne said. "We found that by going beyond broader
exploration scale biozones and pushing the data really hard, well
beyond our comfort zone, we could glean so much more.
"In the production arena we use bug events, delving
into what would be dismissed as background 'noise' at the exploration
scale," he said. "Across a field the use of these local bioevents
can become powerful."
Payne acknowledged that biosteering is not rocket
science — "low cost, low tech, big impact says it neatly," he added.
The subsurface community, however, has been quick
to recognize the technique's value, he said.
"Engineers and geologists understand the value this
tool brings," he said. "No need for them to get involved in the
underpinning buggy detail — just use the results as part of the
geosteering team effort."
During drilling, samples are cut, prepared and analyzed
by a rig site bug man, which typically takes less than two hours.
"Rates of penetration within reservoir can be of
the order of 10 meters per hour, we would only be 20 meters behind
the bit with our results," he noted. "So, if there is a problem
we can provide timely input."
The goal now is to push this new technology into
the global industry.
"This tool has tremendous potential in the deepwater
Gulf of Mexico, Angola, Azerbaijan, Egypt and Trinidad, to name
but a few," he said. "It can work in shallow or deep marine clastics
as well as shallow or deep marine carbonates — it should be considered
wherever you have fossil-bearing rocks around and within your reservoir
and a play to drill high-angle wells."
It's easy to demonstrate what biosteering can bring
to the table in terms of cost savings and enhanced reserves and
BP has proven the technology at several fields around
the world in a wide variety of reservoir types, with impressive
results. For example:
Valhall Field in the Norwegian North Sea, in a Late Cretaceous
deep marine carbonate reservoir.
"We have a six-fold reservoir subdivision in this field," Payne
said. "The Valhall reservoir is a pretty monotonous chalk package
on logs and lithologically, but biostrat can achieve a fine layering
in the chalk, and biosteering technology has made it possible
to stay within the target horizon while drilling horizontally.
"The target zone is actually below the highest porosity zone,
because the highest porosity layer is unstable and prone to collapse
when it is drawn down," Payne said. "By drilling just below this
zone we avoid the problem of collapse but we gain good production."
Specifically, 25 percent of Valhall production can be attributed
to placing the wells in the optimal part of the reservoir through
Cusiana Field in Colombia, a giant field that produces
from several formations, including the Cretaceous Guadalupe Formation.
"We can break the reservoir into a number of units on the basis
of high resolution biostrat," Payne said. "The time slices come
down to a few tens of feet, which allows us to determine with
a high degree of certainty where we are around the reservoir.
"Biosteering across a faulted reservoir section helps keep the
wellbore on target," he added.
The high-angle biosteered wells have the potential to generate
two to three times the production of conventional wells.
Sajaa Field in Sharjah, where one of the key intervals
can be broken down into 14 biozones across 1,000 feet.
"We drilled over 15 wells, including multi-laterals, supported
by biosteering technology," Payne said, "and the tool was particularly
useful here due to structural complexity, including sub-seismic
faults that cut the reservoir.
"When we come out of the reservoir due to one of these faults,
we have to know where the reservoir is so we can steer the well
back into the target zone," he said.
"The technique definitely saved time and money at this field
by averting potential side tracks."