Carbonate Pore Systems: New Developments and Case Studies
Characterizing the Distribution of Natural Fractures from Outcrop in a Mississippian‐Aged Mixed Carbonate‐Chert System, Mid‐Continent, USA
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Published:January 01, 2019
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CiteCitation
Yulun Wang, G. Michael Grammer, 2019. "Characterizing the Distribution of Natural Fractures from Outcrop in a Mississippian‐Aged Mixed Carbonate‐Chert System, Mid‐Continent, USA", Carbonate Pore Systems: New Developments and Case Studies, Donald F. McNeill, Paul (Mitch) Harris, Eugene C. Rankey, Jean C.C. Hsieh
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Natural fractures are common in the unconventional “Mississippian Limestone” play of the US Southern Mid-Continent region. Owing to their narrow width, vertical cores provide limited data on the distribution of fracture attributes (e.g., kinematic aperture, height, and spacing) in relation to fracture abundance. For the purpose of searching for an outcrop analog that provides an extensive view of lateral fracture distribution, this study uses an outcrop with Mississippian-aged strata in northwestern Arkansas. Targeting the Reeds Spring Formation, this study aims to characterize the type, attributes, and distribution of natural fractures and to test the outcrop’s suitability as a fracture analog for the subsurface. In the outcrop, planar and nodular beds of lime mudstone and chert contain near-vertical cemented fractures. Fracture types mainly include ptygmatic and opening-mode fractures. Ptygmatic fractures are the most common fracture type in both lime mudstone and chert, whereas the opening-mode fractures are present mostly in chert. Bedding structures, which are defined by lime mudstone–chert variations, affect fracture growth, as indicated by the observation that perfect bed-bounded, top- or base-bounded, and confined fractures collectively account for the majority of the fracture population. In terms of fracture intensity, chert shows a higher average value as compared with lime mudstone. Negative exponential and power law are present as the statistical patterns between cumulative frequency and fracture height, kinematic aperture, aspect ratio, and spacing. The best-fitting distribution pattern and the coefficient of determination vary with lithology, fracture type, and fracture height. These patterns likely point to a cooperative role of lithology, fracture type, and fracture-bedding relationships, as well as the dynamics of rock mechanical properties, in affecting these fracture attributes. In comparison with the cores, this outcrop may serve as a fracture analog for the Mississippian Limestone play in northernmost Oklahoma–southernmost Kansas where cherty facies are widespread, but not for the play areas in north-central Oklahoma, which are dominated by mixed carbonate–siliciclastic facies.
- Arkansas
- bedding
- brecciation
- carbonate rocks
- carbonates
- Carboniferous
- chemically precipitated rocks
- chert
- clastic rocks
- folds
- fractures
- hardness
- hydraulic fracturing
- Kansas
- kinematics
- Midcontinent
- Mississippian
- mudstone
- Oklahoma
- Paleozoic
- petroleum
- planar bedding structures
- power law
- precipitation
- ptygmatic folds
- rock mechanics
- sedimentary rocks
- sedimentary structures
- stress
- United States
- Reeds Spring Formation
- unconventional reservoirs