A couple of years ago Excalibur Exploration Inc. drilled two wells that "looked like they were going to be truly spectacular," says Dave Harker, president of the Greentown, Ohio-based company.

Excalibur is a privately owned E&P with assets, including 50 wells, in the Clinton, Rose Run and Trenton-Black River formations in Ohio and the Rome Trough near Winchester, Kentucky.

"We had one of the major fracturing companies ask us to try some new technology in the Clinton wells, and they looked like they would be good candidates, worth the expense," he says. The wells were subsequently hydraulically fractured with 50,000 pounds of sand.

The formation, in Geauga County, is a prolific producing reservoir in a delta-shelf environment with numerous bars and channels. Average porosity is about 9%, and average permeability is low, about 0.1 milliDarcies, without natural fractures. The Clinton, encountered at 4,100 feet, has net thickness of about 105 feet and bottomhole temperature of 100° Fahrenheit. Pressure depletion is the primary producing mechanism, and the formation usually requires hydraulic fracture-stimulation with proppant.

"We used the technology, but we learned that both fracture jobs did not go well. In the end we had very high pressures, which we never want to see in these wells."

Harker says the service company initially claimed the pressures were confined to the drillpipe and were not transmitted to the formation. The well was put on artificial-lift equipment in March 2005, some five months after the fracture process.

"When we were completing the well after the fracture job, it seemed to flow normally. We saw oil and gas shows. We shut the wells in, completed them, built pipelines and tank batteries and put the pumpjacks on. Then, when we turned them on, all they did was make water."

The initial production rate was 85 barrels of water per day, with no oil or gas. Harker says there was not even enough gas produced to run the pumpjacks, so he arranged to have propane delivered to run the motors.

"We pumped them for quite a while, thinking they would clean up. We started testing the water and found that it contained large amounts of chloride, much higher than what we had anticipated for a Clinton formation. It turns out we had connected with a very water-prolific zone above the Clinton, called the Newberg. And those waters just cascaded down, drowning out the reservoir. We had fractured out-of-zone."

Excalibur shut the wells in for a year, searching for any way possible to rehabilitate them, such as diesel cement corrections. "We ran across this Marcit treatment, developed and licensed by Amoco, to companies like Tiorco."







New application

Tiorco Inc., based in Denver, provides chemically enhanced oil-recovery technologies used in North and South America, Russia, China and Asia. The Marcit treatment, a water-influx-reducing gel treatment, caught Harker's interest. The Marcit process uses a polymer gel of water-dissolved polyacrylamide with added chromium III cross-linker to initiate the gelation process. The gelant solution is injected as a low-viscosity liquid that solidifies over time.

"We talked to the engineers at Tiorco. This is a completely new application of the product, different from the ways it had been used before. It also had never been used east of the Mississippi River, so this was quite a step out for them as well as for us," says Harker.

Previously, Tiorco used the gel technology for customers with naturally fractured, producing wells and water-injection wells for waterfloods. The gel can channel water back into intended zones during water breakthrough. Excalibur intended to use it to keep the water from coming into the wells at all.

"We had a very steep learning curve. We started the project the way the engineers designed it. On the first well, we probably pumped more into the well than we should have. When you pump this gel in, it has a similar viscosity to water and tends to follow the path of least resistance. In our case, we hoped that path would be the fracture channel that allowed the water to come down into the well," he says.

The gel was pumped into the first well at extremely slow rates, literally taking a full day. Harker determined that, as gel was pumped in, the well started to approach pressures seen at the start of the fracture process, and when it equalized, he assumed the job was done.

"For the next well, we pumped in considerably less, and the second well has worked out much better. After we pumped in the gel, we shut the well in for a couple of weeks so the gel can change from a liquid to a soft, but fairly strong, rubber-like product to seal off the water."

The first well is not very successful, he says. Excalibur is producing enough gas for positive cash flow, but he predicts that it is never going to be a great well.

"The second well is doing pretty good. It's going to be a nice commercial well. We are trying this again on some other wells with water problems. Before this treatment, some of these wells were making 85 barrels of water per day. Now we have them pretty much dried up.

"We are getting somewhere between 11 to 14 barrels of water per day, so they are showing initial success. They are also showing some oil, and are running on their own power, so they've got gas and are pressured up. Still, we might have to pump them out for months before we can tell for certain just how good they are going to be. I'm confident they will eventually start making some significant money," he says.

Altogether, Excalibur used the gel technique on five wells. "If we were to have these problems arise in the future, I'm sure that we would try this remedy again because of the success we had with this treatment. We have roughly 4,000 to 5,000 acres in this area, and we plan to continue to drill wells. Now we know that, if there is a problem with a fracture job, this is a possible solution for going back and correcting it."

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