By KIRSTEN LEATHERDALE, of the Weyburn Review
PanCanadian's oil-rich Weyburn field has been chosen for a new form of seismic testing, in part developed by Creelman farmer and geophysicist Tom Davis, which could have major implications for Weyburn and the oil industry in general.
If the $3.2 million study produces the expected results, the life of the Weyburn oilfield could be extended 25 to 30 years. The study, dubbed the Reservoir Characterization Project, is funded by a consortium of industry partners and the Department of Geophysics at the Colorado School of Mines, where Davis teaches through part of the year.
"It has the potential for being technology that can help determine the patterns of wells and the locations of wells to get more oil out. It has economic meaning to PanCanadian, our other sponsors, and the people of southern Saskatchewan. Everyone benefits if this works," said Dr. Davis in a telephone interview from his office at the Colorado School of Mines, where he is head of the department of geophysics.
The study contains three elements: three-dimensional seismic testing, an injection of carbon dioxide into the field, and the recording of data over a period of time.
"Three-dimensional testing, as it's normally done, records only vertical ground motion. What I've done that's new is to record all the aspects of ground motion - not just vertically but horizontally as well," said Davis.
The horizontal motion is called a shear wave. Davis and his colleagues will induce this kind of ground motion, using a truck-mounted hydraulic vibrator with small teeth on the baseplate that shakes the ground sideways. The waves that are produced will travel into the subsurface and bounce off the subterranean formations, then come back to the surface, and be recorded.
"We've discovered by looking at shear waves, that they are more sensitive to measuring sub-surface changes," he said.
The initial seismic test will be conducted in the winter of 1999-2000, after harvest is completed and before PanCanadian's planned flood of the field with carbon dioxide.
The purpose of the flood is to have carbon dioxide mix with oil trapped in rock formations, causing the oil in the porous rock to be released and flow more easily. It becomes a lighter, less dense fluid, with a lower viscosity.
One test will be conducted before the C02 is in, and a series of seismic shoots will occur after. Only a small portion of the field, four or five square miles, will be tested.
"We take the difference between these two surveys to see the changes in the reservoir," said Davis.
"C02 is mobile, so it can flow sometimes in directions you would prefer it not to. It's controlled by the formation itself. What we want to know is where is this stuff going? If, in certain zones the C02 injection goes very quickly into the fractures and doesn't contact the oil, then it's not doing what it's supposed to do, and economically that could be a disaster.
"With the first survey, we see the subsurface, and any problems that may occur. With the subsequent surveys, we can then confirm where the C02 is going. It's like taking snapshots over time, seeing waves of C02 move out into formation, how they are interconnected and how they push from the injection areas to producing wells," Davis explained.
Alan Boras, director of media relations for PanCanadian, confirmed Dakota Gas will be the supplier of C02 for the Weyburn oilfield, and will build the pipeline bringing the gas into the field. He estimates construction on the pipeline, which has been delayed several times due to funding problems, will begin in the summer of 2000.
PanCanadian was up against some heavy hcompetition in the oil industry to get the test done on their field. The number two choice for the project was Exxon's field near Midland, Texas, and the number three choice was the EcoFisk field in the north-central part of the North Sea.
"We chose the Weyburn field because of its economic potential, and the right time of start up. We wanted to employ the technology before the start of the C02 flood, to correct problems at the earliest possible stage," Davis explained.
He said Weyburn is where the $3.2 million in funding can be used to the best advantage - the frozen ground conditions will be ideal for the horizontal seismic activity, and the costs related to the test will be low.
Weyburn was also chosen because of its horizontal wells, where subsurface sensors can be more easily placed to listen right at the reservoir level.
"We were very pleased to be chosen. It's quite an honour to be selected from a group of big pools with big company names behind them. We were somewhat surprised they chose a Canadian pool with a Canadian operator - given that it's a multi-national venue," said Catherine Chaplin, a geologist working out of PanCanadian's Calgary office.
As far as Davis was concerned, it just made sense not to walk away from the Weyburn field, where only 330 million barrels of oil have been produced from a field that holds 1.5 billion barrels.
As an additional bonus, the tests he conducts could have a huge economic impact for towns and cities throughout the southeast, including Creelman where he grew up and still owns a farm. After graduating high school, Davis went to the University of Saskatchewan and completed a degree in geological engineering, then to the University of Calgary where he did his MA, and worked in the oil industry for three years. He headed south to do his doctorate work in geophysics at the Colorado School of Mines, and has been involved in the study of seismic recording methods ever since.
"Seventy per cent of the oil that we know of today is contained in giant fields that have already been found. The thing to do is use integrated technologies to recover oil from the fields, and places like Weyburn are the place to go," he said.
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