November 2006 ISSUE
INSIGHT
Academia and Industry Further the Art and Science of Finding and Characterizing Fractures
BY SUSAN R. EATON, P.GEOL., P.GEOPH.
PEGG Contributor
 |
FRACTURED TURTLE Research drilling in Alberta’s infamous Turtle Mountain — site of the Frank Slide a century ago — doesn’t strike oil and gas. Data collected there, however, could help the Fold-Fault Research Project predict sweet spots elsewhere. -Photo Courtesy Dr. Robert Stewart, P.Geoph. |
Fractures in subsurface geological formations are important to the oil and gas industry. In fact they play a critical role in the development of permeability, enhancing the delivery of oil and gas to well bores.
The detection and characterization of fractures — including their orientation, density and age of generation — represent not only an art form but a rigorous study in structural geology.
In Alberta’s Western Canadian Sedimentary Basin, where oil and gas companies have shifted their exploration focus to tighter reservoirs in the foothills and the deep basin, the presence of open fractures can make — or break — a commercial well.
Despite the economic importance of fractures, most geologists in Calgary’s downtown oil patch practice “desk-top geology,” creating maps of the subsurface — but rarely visiting the field to measure fractures in rocks outcropping at the surface. During the past two decades, the loss of in-house research and development capabilities in the global oil and gas industry has left a void in technical expertise in structural geology.
However, a unique research and development partnership, based upon mutual strengths, is developing between the oil and gas sector and academic institutions across Canada. Oil companies supply proprietary data sets and badly needed research money; in turn, universities procure masters and doctoral graduate students with professorial supervision.
Academia-Industry Synergy
Dr. Deborah Spratt, P.Geol., is a professor of geology at the University of Calgary’s
Department of Geology and Geophysics. Dr. Spratt specializes in structural geology,
studying fractures from “the micro scale to the seismic scale to the mountain-building
scale.”
Her academic research is largely focused on predicting where open fractures will deliver oil and gas to well bores from subsurface reservoirs.
“A lot of oil and gas companies have given up on fractures. With fractures,
you really need time, which is what most oil companies don’t have,” Dr.
Spratt says. “Graduate students have time.”
Dr. Spratt’s research in fracture characterization falls under the umbrella
of the Fold-Fault Research Project, which she co-founded in late 1994 with Queen’s
University in Kingston, Ont. In 2003 the project won the the Alberta Ingenuity
Fund Research Excellence Award in the APEGGA Summit Awards.
Since its inception, the FRP has successfully attracted industry funding and participation. In 2005 the consortium included 14 international and Calgary-based oil and gas companies, and five industry software companies.
Integrating field mapping with subsurface seismic and well bore data, Dr. Spratt is studying the role that fractures play in oil and gas exploration and production in the foothills. She’s currently investigating the Pardonet, Baldonnel and Belloy formations in northeastern British Columbia, and the Turner Valley Formation in Central Alberta.
The academic environment affords professors and graduate students the luxury of examining the big structural picture from an unbiased perspective. Malcolm Lamb, P.Geol., one of Dr. Spratt’s doctoral candidates, is in his third year of research.
A Man From Both Camps
Mr. Lamb is a part-time graduate student — that’s because his day
job keeps him very busy. Mr. Lamb is the principal geologist, and data and consulting
services business development manager at Schlumberger Canada Ltd.
With one foot planted firmly in each camp, Mr. Lamb recognizes the value of the academic research being conducted by the Fold-Fault Research Project. “Industry has been in a holding pattern for a long time. It’s created a very competitive playing field between all companies — they don’t like to share information.”
Mr. Lamb describes the project as “an awesome venue, a really good sharing environment.” Institutions such as the University of Calgary, he says, play a huge role in dissemination of information to the oil and gas industry.
There’s a balance that researchers continually strive to achieve, which
Mr. Lamb says is “a blend of academics advancing knowledge while serving
industry needs and providing economic benefits.”
Wearing his graduate student’s hat, Mr. Lamb likes the artistic freedom
to look objectively at a structural geology problem. “I have absolutely
zero stake in whether it works. I can be completely unbiased.”
Through joint ventures with industry, the project’s researchers have access to all the tools available in the structural geologist’s modern-day tool kit — downhole wireline logs, downhole optical sensors and cameras, cores, thin sections, outcrop studies, sophisticated visualization software, aeromagnetic data, and 2-D and 3-D seismic data. These diagnostic tools may have been developed by the oil and gas industry — but university researchers use them in a slightly different way.
“We’re not throwing out data,” explains Dr. Spratt. “Even if our data comes from a dry hole, you can learn something from it.”
She continues, “If you only have two wells, you might think that fractures are random.” But Dr. Spratt’s investigations have led her to just the opposite conclusion — she doesn’t believe that fractures are randomly distributed.
“We’re looking for populations of orientations of fractures, and actually finding some that you wouldn’t predict,” says Dr. Spratt. She describes discovering one extra set of fractures in the foothills of Alberta and British Columbia. In some cases, she says, this newly documented fracture set can be the dominant one in sedimentary strata, adding significantly to the permeability and commerciality of oil- and gas-bearing reservoirs.
Related to deep-seated structures that pre-exist the formation of the Rocky Mountains, this extra set of fractures is not readily predicted with seismic data. But maps produced from aeromagnetic data indicate the existence of older, structural lineaments which parallel this extra set of fractures discovered by Dr. Spratt in the Western Canadian Sedimentary Basin.
Tackling Turtle Mountain
During the summer of 2004, Dr. Spratt and Mr. Lamb conducted field studies on
top of Turtle Mountain in the Crowsnest Pass of Southern Alberta. Infamous for
spawning the Frank Slide in 1903, Turtle Mountain unleashed 82 million tons of
highly fractured limestone, killing 70 people in the coal mining community of
Frank.
In 2003 — exactly a century later — modern-day science was brought to bear when a chunk of rock fell off the highly fractured, front face of the mountain. In response, the Fold-Fault Research Project initiated a geological and geophysical monitoring project to predict future slides.
“I’ve seen fractures on the top of Turtle Mountain — ones that you could drop a mini-van into,” says Dr. Spratt.
To kick off the project, the Fold-Fault Research Project flew a drilling rig and well-logging equipment, via helicopter, to the top of the Turtle Mountain. Drilled with air and foam, the well was designed to reach a depth of 200 metres — but drilling was stopped at 61.3 metres, after the team lost circulation into large, open fractures. Researchers actually feared losing the drill rig into a void space.
The Turtle Mountain well bore was logged, using an Advanced Logic Technology OBI40 digital optical televiewer. The tool consisted of a directional device and an imaging device, providing a 360-degree, continuous picture of the borehole’s surface, with resolution up to 0.5 millimetres and 720 pixels of azimuthal resolution.
A multitude of fractures and vugs — cavities created when crystal erodes within rock —were documented in the well bore, including several large, open fractures. The subsurface data from the well bore was correlated with seismic data and tied back to the surface, using field mapping, ground penetrating radar images and aerial photographs.
“It’s unusual to drill holes into surface structures that don’t produce (oil and gas),” says Dr. Spratt, describing the unique value of the data set collected from the Turtle Mountain project. The formations exposed at surface at Turtle Mountain — when buried at depth — produce prolific quantities of natural gas elsewhere in the foothills of southern Alberta.
By looking at the big picture, and by combining her surface field studies with real-life well bores and seismic data, Dr. Spratt hopes to be able to predict the sweet spots for fractures. “Rather than thinking of each well as its own case study,” she says, “is there a unifying way to predict fractures?”
Scale Over Scale
Dr. Don Lawton, P.Geoph., co-founder of the FRP and a professor of Geophysics
at the University of Calgary, is trying to answer the same question. Dr. Lawton,
who holds the Chair in Exploration Geophysics, is looking for “any diagnostic,
robust signatures” in seismic data in the foothills which point to fractures.
“We would like to use Dr. Spratt’s measurements and observations to validate what we see in the seismic,” says Lawton. “We can only see big things; she looks at small things. But we can overlap our scales.”
For example, a seismic wavelength is about 100 metres — in contrast, Dr. Spratt measures fractures in zones ranging from less than one metre to 50 metres wide. Surface field measurements of fractures and subsurface measurements in well bores provide the necessary “ground truthing” for his seismic investigations, says Dr. Lawton.
“We see changes in seismic velocity with respect to a change in the orientation of fractures,” says Dr. Lawton. Velocity changes, he says, originate from changes in the orientation (azimuth) of fractures relative to the source and receiver layout for seismic data acquisition in the field.
Additionally, Dr. Lawton has noted changes in seismic reflection strengths
or amplitudes derived from fractured layers of rock. He calls this phenomenon
amplitude variation with azimuth, or AVAZ.
Dr. Lawton and the Fold-Fault Research Project’s graduate students are
testing their AVAZ theories on two mystery 3-D seismic data sets, acquired by
the oil and gas industry somewhere in the foothills of the Western Canadian Sedimentary
Basin. A well-recorded 3-D data set, he explains, contains azimuthal information
from zero to 360 degrees.
By extracting different azimuthal subsets (zero to 90 degrees versus 45 to 90 degrees), Dr. Lawton is attempting to correlate differences in seismic azimuths to fracture orientations. To date, his research has yielded “”tantalizing results.”
“It’s just at the beginning of the S-curve of the AVAZ technology,” says Dr. Lawton. “In theory, it should work. It’s just a question of the magnitude.”
Susan R. Eaton, P.Geol., P.Geoph., is a Calgary freelance writer who specializes in science and technology.