You don’t have to be in the United States to know that the country’s ubiquitous shale plays are high impact.
Thanks to the upcoming AAPG International Conference and Exhibition, some of the important exploration innovations that have helped in America will grab a global spotlight.
This year’s ICE, set Oct. 26-29 in Cape Town, South Africa, will include a presentation on integrating new technologies to map structural features and improve stimulation treatments in shale gas plays.
With integration as the overall theme, the talk will focus on coupling surface seismic, microseismic mapping and wireline logs in the now-familiar Fayetteville Shale play in the Arkoma Basin.
The paper to be presented was co-authored by AAPG members Don Burch, senior geophysicist at Aspect Abundant Shale in Golden, Colo., and Joel Herve Le Calvez, senior geologist at Schlumberger in Dallas.
They start with the given: Sizeable volumes of gas currently are being produced from unconventional shale reservoirs such as the Barnett and the Fayetteville in the United States.
Burch goes on to note these plays are driven by both technology and economics, emphasizing that modern well log evaluation techniques and completion methods are required to yield economic wells.
Owing to the extremely low porosity and permeability of these shale reservoirs, they must be stimulated via hydraulic fracturing to achieve effective production volumes.
The stimulation process induces microseismic activity, which allows the geoscientists at the well site to “listen” to the fracture stimulation.
Microseismic hypocentral locations can be determined in a matter of seconds using advanced processing algorithms and transmission techniques to process large volumes of data on-site.
By monitoring the induced microseismic, the geoscience team can avoid making too many assumptions about the fracture stimulation geometry.
The Fayetteville Details
Employing an example from Aspect’s former operations in the Fayetteville Shale, Burch said the upcoming presentation will highlight the integration of real-time microseismic monitoring of hydraulic fracture treatments with surface seismic data to:
- Detect potential sub-seismic scale structural geohazards.
- Verify interpreted fault geometries.
- Allow on-the-fly changes in fracture stimulation design to maximize the reservoir volume effectively contacted by the stimulation treatment.
Aspect methodically honed its approach to the Fayetteville operation.
“We had surface 3-D seismic in the area with some level of interpretation, and we identified structure and picked some faults and things like that,” Burch said. “But as far as calibrating our fault identification to its impact on our stimulation we didn’t have any information.
“Likewise we had a complete wireline suite,” he said, “and although you can do some one-dimensional work and look for fracture boundaries and mechanical properties changes and things like that, you are limited in your extrapolation into the seismic data by a variety of assumptions there.
“The microseismic ultimately tied things together because it allowed us to confirm existence of faults we were picking in the seismic as well as their geometry.”
“The geometry was important,” Burch noted, “with respect to the risk associated with a particular fault – were you going to open that fault up in the direction of a water bearing formation, or was it going to open harmlessly into an area with no resource but didn’t represent a water hazard?
Real Time
Burch said that his team was able “to basically tie the whole story together.
“We calibrated our surface seismic data, and from the petrophysics we could tell what sort of influence that particular fracture stage was going to have if it went somewhere we didn’t intend it to go.
“We would know if it was headed for a water risk, in which case in the field doing this live, we’d back out of the throttle on the frac and stop the propagation along that fault,” Burch said.
“Conversely, when we saw one of these faults go up through a frac barrier into a zone of no resource, we’d let that particular stage run because we weren’t risking a water hazard and might still be able to capture a little bit of resource from that particular zone.”
This whole story is a lesson about the importance of having a geoscientist on site armed with the equipment to provide real time feedback during fracture stimulation.
“Joel and I sat in the truck at 2 a.m. with him bringing data into his machine, and I’m taking that directly off and putting it into my 3-D model,” Burch said. “We’re making on-the-fly and on-the-ground decisions about how the fracture is going, and we’re talking to the guys with their foot on the throttle – that turned out to be key in the overall performance of a particular fracture.
“Having the ability to cohesively tie together a model and calibrate things in real time in the field when you’re doing fracture stimulation was fundamentally important,” Burch said.
A noteworthy feature of the upcoming presentation in Cape Town is how to QC the data on-the-fly in the field.
“You need to have a confidence in each of these events you can place because you’re going to have to draw conclusions based on when they occur and where they occur,” Burch said, “and there are errors associated with that.”