A University of Texas pilot study shows many operators are already doing the right thing when it comes to extracting oil from the East Texas Oil Field.
The study, funded by the State of Texas Advance Resource Recovery (STARR) program, took about 14 months to complete, said Eric Potter, associate director of the Bureau of Economic Geology, part of UT's John A. and Katherine G. Jackson School of Geosciences. The study's findings were reported Tuesday during a workshop at Meadowbrook Country Club in Kilgore.
The STARR program study was conducted on small, select areas of the field, and modern methods of reservoir characterization were used. Gregg County was the northern pilot area where the study focused on locating untapped oil; Rusk County was the southern pilot area where the focus was locating oil unswept by waterflood.
"We wanted to take a brand new look at some small areas of the field and apply modern concepts of geologic thinking, and say, 'What does the reservoir architecture look like? ... How would we view that in modern times and would that make an impact on how the operators produce the field?'" Potter said.
The study prepared a detailed geologic picture of how the Woodbine formation looks in the two pilot areas.
The study took core samples and examined the oil deposition in the rocks.
"Hardly anybody looks at the rocks anymore, so we went back and looked at the rocks," Potter said. "And then we worked up a detailed geologic picture of how the Woodbine, the producing formation, looks in three dimensions in these two pilot areas."
This led to the study group's arrival at some recommendations on how operators could possibly make the most out of production in the ETOF.
"In many cases, it was affirming what operators are already doing," Potter said. "In a couple of instances we made some suggestions for things that might be done better."
Operators are now drilling deeper into the Woodbine to reach untapped sands that might have oil in them, Potter said.
"They're doing a nice job with that, and we're encouraging them to do more, based on the detailed geology that we showed them in the presentation," he said. "The other thing operators are doing a lot of is waterflood, where you push the oil from an area where you inject water to water wells where you're producing presumably more oil as a result of the waterflood."
The oil is separated from the water, which is injected back into the ground.
He said the study group talked to the operators about more efficient ways to extract oil using waterflood and of the importance of working together. Potter acknowledged, however, competition among operators and legal issues would make that second recommendation very difficult to carry out.
But Fred Marshall, a consultant for SND Energy in Kilgore, said the information the study group presented was valuable.
"I'm a petroleum geologist and the work today, primarily on these cores like we're studying right now, is all hard rock geology, and we're seeing the details in the rocks that you can't see on the electric logs," Marshall said. "You're starting to understanding the geology and deposition of environments that these cores are showing. Then you can go back to the electric log and you can interpret off of the electric log to the next well."
Potter said the endeavor was a "pilot" study, only examining two areas of the field rather than the entire field. But he was confident in saying the "gold mine" of oil that used to lie beneath the East Texas earth has been extracted.
"When this field was discovered, there were 7 billion barrels of oil in it, and 5.4 (billion) have been produced," he said. "And then 1 billion you're not going to be able to get out because it's bound to the rock. We call that residual oil."
That leaves about 550 million barrels of what Potter called "unfinished business."
"Of that, we think the operators will get about 60 million to 70 million barrels using their current approach," he said. "That leaves about 400-and-something million barrels of oil that's still out there in the field - mobile oil that could be gotten if we knew where it was and could efficiently go after it."
The ETOF has 31,000 wells in it, of which about 4,000 are still operating, Potter said. Most of the wells are plugged.
As for existing wells, it is difficult to know exactly where the oil is in those wells, because the field is producing massive amounts of water. Of all the liquid that comes out of the field each day, 99 percent of it is water, which is separated from the oil and injected back into the ground.
"We're producing so much water with the oil, that we're not exactly sure which zones the oil is coming out of anymore," he said. "There are some questions, and if we could know with more precision where the oil is coming from, then we could make recommendations about how to do a better job getting it."
He said the study group believes that information is on paper in the operators' offices, but "it would take an army of people a long time to get all of that information," even if a study group obtained permission from the operators to get this private information.
The field produces about 11,000 barrels of oil a day; at its peak in the 1940s it produced more than 500,000 barrels of oil a day.
Potter said the study group projects operators, using today's methods, will be able to produce oil in the ETOF to the year 2030.