Calibrate Stress with Pressure
Data Science & Analytics

Calibrate Stress with Pressure

Rosemary Jackson  •  

Q: Why are DFITs and ISIPs so important?

A: “Let me tell you the cool way to look at this,” Dr. Nitin Chaudhary, Senior Data Scientist, begins, "Ordinarily, operators would not have done DFIT or even if they would have done a DFIT it would have been as an input for some complex reservoir simulator. is the only solution that uses the DFIT in a very unique way from a context that goes beyond what a frac simulator derives. not only models where the fracture is going to grow, we take that observation one step further and calculate productivity from it as well as economics. can plan your pad out completely. A DFIT and ISIP being two of the key measurements that go into that modeling process.

“A whole new use case is opened up for operators which is much more impactful and much less isolated than the way companies have been historically using DFIT or ISIP measurements.

Automated ISIP Detection

“One other point is that DFITs are great, but most people don’t do them because you have to spend money on equipment, rig time and then you have to shut down your well or time it out before you start your well. So, all of that delaying time costs money. Companies don’t use ISIPs because there is no automated way of picking ISIPs. Companies aggregate all this completion data and it’s usually just sitting there in some pdf or spreadsheet and the information goes unused. can work all that historical completion data into building highly accurate stress profiles that we feed into our productivity model.

“This opens up a new kind of use case for completion data.”

“Right,” Dr. Brendon Hall, VP of Geoscience agrees. "There’s not a lot of existing workflows that use the DFIT.

“A DFIT is a test during which one of the things you want to measure is the ISIP value, the instantaneous shut-in pressure. You perform a DFIT to get a good measurement of the ISIP. You can also measure ISIPs during other activities most notably when you’re pumping a frac stage where you can measure the ISIP that occurs at the end of that stage. After you stop pumping and the frac closes you can get an ISIP measurement.

The reason you want to do that is because these stress measurements are the best way you can get an accurate calculation for the minimum horizontal stress in the earth.ISIPs and DFITs are good calibration points for a subsurface model.

Frac Gradient, Frac Geometry, Reservoir Drainage

Dr. Mark Zoback, Technical Advisor and Professor of Geoscience at Stanford University has developed a workflow for this. What he likes to do is look at as many stress measurements, as DFITs and ISIPs, as possible. This gives you points in the earth, ideally along a vertical profile where you can measure stress. Then Zoback likes to bring in well logs to provide a more continuous measurement over that interval, most notably the clay plus TOC which can give you an indication of how much stress relaxation can happen to the well. Using those two curves Zoback has a methodology for interpreting a stress profile using those calibration points.

“Why you want to do this, is why geomechanics is important. You want an accurate characterization of where potential stress barriers are, to know if fracs are going to go up or grow out, how they’re going to interact with one another. That modeling of the subsurface starts with the frac gradient developed from DFITs and ISIPs.”

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