Once again we visit the debate over whether seismic technology has any use in unconventional reservoirs. But this time we’re not talking about using it as an exploration tool or even a tool like microseismic that monitors the reservoir as it’s being fractured. We’re talking long-term reservoir monitoring with a new source technology that isn’t even in the prototype stage yet.
The issue with fractures is that they tend to close over time due to changes in the stress field. Operators find themselves needing to refrac wells periodically to reopen these sealed fractures. The proposed source technology would reside in a rathole in the bottom of a producing well or in a shallow offset well. Operators could take frequent snapshots of their reservoirs by permanently installing receivers near the surface. Over time this would lead to a tomographic image of the reservoir.
Jim Applegate, CEO of Pegasus Oil & Gas Inc. in Denver, is a proponent of this new technology being developed by Owen Jones, cofounder and CEO of Argus Reservoir Monitoring Inc.
“This would give operators a sound reason to decide to refrac one well over one interval rather than blanketfracing the whole well or fracing every well in an area,” he said. “That’s where the costs are in this operation.”
There are several advantages to having a subsurface source, he said. For one thing, it removes the necessity of bringing surface sources such as vibrator trucks into an operating oil or gas field – a huge advantage in places like the Marcellus shale with difficult topography. Second, it eliminates the need for the sound waves to travel through the weathered region in the near surface, which can wreak havoc on the energy and frequency content of the signal. Also, it is yet another way to scientifically prove to the naysayers that the fractures being created in shale reservoirs are not affecting shallow aquifers.
But like any good time-lapse program, whether conventional or unconventional, the biggest benefit is simply getting to know the reservoir a little bit better. “We know there are bypassed hydrocarbons in these fields,” Applegate said. “We know that the sweep of our production, whether it’s initial, secondary, or tertiary, is not complete. By putting five to 10 sources, you can monitor the movement of the fluids.
“If you can increase the productivity in a field by 10% or 20%, that more than pays for the system and the monitoring,” he added.
What’s needed to bring this technology to fruition is, not surprisingly, funding. Applegate and Jones have talked to a few companies but are wary of intellectual property issues. “I believe it’s going to take somebody who has vision, some real insight,” Applegate said. “It’ll take a wealthy individual or a service company willing to risk some money to test the concept. But even if it costs [US] $5 million, that’s a cheap Marcellus well.”
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