Greg Pence, MTS Applications Engineer
Global Custom Aero & Infrastructure Group
Properly characterizing rock formation properties is crucial in helping petroleum engineers determine what methods to use to maximize production.
Rock Mechanics Testing Helps Oil and Gas Producers ThriveIn the second of a two-part interview, Greg Pence, MTS Application Engineer, Rock Mechanics, discusses hydraulic fracture and explains how MTS test solutions support efforts by oil and gas companies to improve efficiency while making more informed, profitable decisions.
Q: How do the challenges of resource extraction change when it comes to natural gas?
Pence: Hydraulic fracturing, or “fracking,” is getting a lot of attention these days. It’s not a new technique, but application advances have made it an efficient way to access natural gas reserves stored in so-called “tight rock” formations, such as shale. Shale’s very low permeability means it does not permit the flow of material through its pore structure. By closely studying the properties of these formations, companies have developed new ways to extract natural gas from shale reserves. All of the challenges in this application are driven by the unique qualities of shale.
Q: Can you elaborate on the challenges shale poses?
Pence: Shale is very different than rock, and even the most experienced engineers are having to adjust their mindset to understand this geomaterial better. It’s a mix of flakes of clay minerals as well as silt-sized particles of other minerals. It reacts differently as stress states change. In addition, it is deposited in layers that are shallow relative to their length, so companies must use horizontal drilling to access the formations. Horizontal wells are perforated with explosive charges and then hydraulic fracturing is induced by pumping high-pressure fluids into the perforations, which opens up a “fracture network” and allows the resources to be extracted. Predicting all of these interactions is a new challenge.
Q: What kind of data does rock mechanics testing deliver in this application?
Pence: Our customers collect core drillings from the shale formations, and then from these we take multiple smaller core samples, in multiple orientations. The fracture properties of the material can be studied using rock mechanics tests, as well as its matrix permeability. For example, at the onset of fracture, shale reservoirs typically exhibit a high rate of production followed by a slow, gradual decline as the gas moves across the matrix into the fracture network. Understanding these responses helps companies perform recovery economically and efficiently.
Q: What kind of test systems are used to perform rock mechanics tests?
Pence: Triaxial testing enables the simulation of in-situ conditions found in oil and gas reservoir formations. Specifically, triaxial cells can recreate the in-situ overburden and lateral stresses, as well as the temperature of formations and fluid pressures within the rock. Triaxial testing also offers a way to simulate pore fluid flow conditions in the rock. Once the in-situ conditions are replicated, our test solutions allow oil and gas engineers to control the conditions and change the stress states to understand precisely how formations will respond to specific events.
Q: What is the range of temperatures and pressures that can be replicated?
Pence: Our systems can reproduce pressures up to 30,000 psi and temperatures up to 400° F. These capabilities are unique in the marketplace. Our rock mechanics test systems are designed to perform a wide variety of tests, which is also sets our systems apart.
Q: Why is the flexibility of the test system important?
Pence: Customers have a number of choices when it comes to rock mechanics testing. Many of the available systems are made to perform one kind of test that characterizes one aspect of the rock formation. We design our systems to help generate insight about every aspect of the formation, during all phases of exploration, well completion and production. This makes each system more valuable to the customer, because they can complete more tests more quickly. Core samples are expensive to obtain, and turnaround time needs to be quick. Flexible test systems not only improve test productivity, they create opportunities for different groups — the lab team, the cementing group, the drill string group, the fracturing group — to use the same system for their own purposes. Our systems also make it easier to run new tests, or tests the customer did not anticipate they would need, but do.
Q: What sort of customization do these test systems support?
Pence: Flexible design lends itself to a great deal of customization for highly specialized test applications. Our system provides the platform, and our customers build on it to accommodate many different kinds of tests. They are always pushing the boundaries of the technology and finding better ways to characterize rock formations more accurately. That’s how the big problems get solved. And so we welcome the opportunity to collaborate with our customers to address new issues, whether it’s ultra-deepwater drilling, or CO2 sequestration, or preventing subsidance, or combining triaxial testing with acoustic emissions and ultrasonic velocity data. We want to help our customers solve new challenges in new ways.
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