52nd U.S. Rock Mechanics/Geomechanics Symposium,
2018. American Rock Mechanics Association
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ABSTRACT: Hydraulic stimulation and production-induced permeability alteration in stress-sensitive Monterey Formation rocks require an in-depth understanding of the deformation behavior of different rock types. Here, we evaluate and compare deformation behavior of two types of clastic rocks—shale and sandstone—across nano-to-micro scales using experiments and simulations. Using core samples of shale from the Monterey Formation and tight sandstone from the Dominguez Hills in California, we conduct nanoindentation, scanning electron microscopy and particle-based simulation to understand the difference in deformation behavior of shale and sandstone under different loading-unloading conditions. We quantify Young’s modulus, hardness modulus, and stiffness of the rocks using nanoindentation data. Our work provides important insights into grain-scale deformation behavior of two different rock types commonly found in petroleum reservoirs. Understanding of grain-scale failure mechanisms can inform development of new upscaled constitutive models for usage in continuum-scale field simulations, which cannot afford to resolve the grain-scale processes due to computational cost.
Hydraulic fracturing in conjunction with directional drilling has been a game-changing technology for the development of oil and gas resources. It has unlocked vast oil and gas resources in shales and low permeability sandstones which were once considered unfit for commercial production. However, the success of hydraulic fracturing has not been uniform across different types of shales and sandstones. For example, the potential for unlocking millions of barrels of oil from Monterey Formation, California by hydraulic fracturing has been a topic of much debate (EIA, 2011; USC, 2013; EIA, 2014; USGS, 2015). Belridge diatomite, a part of Monterey Formation, has been produced successfully by increasing its low matrix permeability with hydraulic fracturing in 1970-80s. However, the Belridge Field is also well-known for production-induced subsidence and widespread casing failures (Fredrich et al., 1996). Diatomite rock is highly stress-sensitive and can experience pore collapse, reservoir compaction, and induced fracturing due to pressure depletion during production. Our lack of understanding of the geomechanical processes and properties in a geologically complex rock such as Monterey prevents us from designing successful hydraulic stimulation and pressure depletion strategies.
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