Chapter 8: Characteristics of Natural Fractures in Carbonate Strata
John C. Lorenz, Helen E. Farrell, Catherine L. Hanks, William D. Rizer, Mark D. Sonnenfeld, 1997. "Characteristics of Natural Fractures in Carbonate Strata", Carbonate Seismology, Ibrahim Palaz, Kurt J. Marfurt
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Natural fractures are present in carbonates in settings ranging from undeformed, near-horizontal beds to fold and thrust belts. Most fractures in the carbonate examples described here show evidence of an origin in extension. Lithology is one of the primary controls on fracturing; dolomites and dolomitic mudstones are typically more intensely fractured than limestones, and fractures are commonly limited vertically by shale breaks. Structural position is another important control on fracture character, with more fractures occurring at the hinges of folds than on fold limbs. Fractures caused by faulting in moderately deformed strata are commonly present only within 100 m or less of the fault. Older fractures may be overprinted by younger fracture sets in the more highly deformed strata. Structure, petrofacies, and lithofacies combine to control fracture characteristics in the thicker mechanical units under these conditions. Different types of karsted zones may also be superimposed on fractured carbonate strata.