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 first of a two-part interview, Greg Pence, MTS Application Engineer, discusses the challenges oil and gas companies face during exploration and production.
Q: What is the primary challenge oil and gas producers face?
Pence: Oil and gas companies continue to look to extract energy resources from locations that are more and more difficult to reach, and from formation properties that require new techniques for extraction. These are extreme environments in terms of temperature pressure, and the types of rocks found there. It is very difficult to predict how rock formations change, react to stress and potentially fail during the process of drilling, well completion and production.
Q: What role does rock mechanics testing play?
Pence: Rock mechanics is a critical part of a much larger effort. It enables oil and gas producers to characterize the properties of rock formations. Oil and gas researchers use advanced computer-based modeling techniques to predict overall formation properties. Rock mechanics laboratory tests, combined with the results of field-collected or down-hole analysis provide the input parameters for these advanced models. Test data from rock core samples can provide a “reality check,” helping companies refine these models and make them more accurate. Being able to accurately characterize underground formation properties is very important for scenario planning and decision-making related to every aspect of oil and gas exploration and production.
Q: What are some of the specific challenges rock mechanics testing can address?
Pence: Well drilling is a big one. Wells can fail at the wall, in compression or tension, if the pressure of the drilling mud is not properly aligned with the stress conditions and mechanical properties of the different layers of rock. And the deeper you drill, the narrower the window of suitable drill mud properties becomes. Companies use the rock mechanical property data to help determine the best drilling conditions and technologies: what kind of drill bits to use, what type of mud (oil-based or water-based), what pressure to maintain, etc. Rock triaxial test systems are also used to study the casing cements that are used to line and isolate wells during completion. Cement failures can cause well collapse, or allow the escape and migration of harmful gases across geological layers.
Q: What challenges emerge during recovery and production?
Pence: Formation rock consists of material and fluid under internal and external states of stress. When these stress states are understood, companies can better predict how the materials will react under changing states of stress, during draw-down, for example. When a formation is opened and the fluid is removed, internal (or pore fluid) pressure drops, and the rock starts to consolidate, potentially causing pore collapse and failure. Understanding the failure envelope — how, when and why the failure occurs, as well as how fast it happens once it starts — helps petroleum engineers determine what methods to use during production, which draw-down rates will maximize production, and which methods should be used to stimulate production if problems occur.
Q: What other characteristics do MTS solutions help oil and gas producers understand?
Pence: Susceptibility to sanding is an important characteristic to explore, especially in areas with poorly cemented rock. Even when the well pressure is correct, sand and rock can erode from the perimeter of the hole and work its way into the mud. This not only changes the density of the mud, it can damage the pumps used to deliver drilling mud or extract oil. Sand production is also a concern for fractured wells, where excess sanding can interfere with extraction efforts. For a given sample, we replicate and manipulate the axial and confining stresses, as well as the pore or borehole pressures, to understand when and how sanding can occur so companies can avoid these conditions at the well site.
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