ABSTRACT

Geometric attributes such as coherence and curvature have been very successful in delineating faults in sedimentary basins. Albeit not a common exploration objective, fractured and faulted basement forms important reservoirs in Southern California, Mexico, India, Yemen, and Vietnam. Basement faulting controls hydrothermally altered dolomite in the Appalachian Basin of the USA, and is suspected to play a role in diagenetic alteration of carbonates in the Fort Worth Basin of north Texas where copper has been found in some wells, as well as in Osage County, Oklahoma, not far from the classic Mississippi type lead-zinc deposits. Because of the absence of stratified, coherent reflectors, illumination of basement faults is more problematic than illumination of faults within the sedimentary column. To address these limitations, we make simple modifications to well-established vector attributes including structural dip, azimuth, and amplitude gradients, in combination with variance, and most positive and most negative principal curvature to provide greater interpreter interaction. Using these methods, we can better illuminate fracture “sweet spots” and estimate their intensity and orientation. We apply these methods to better characterize faults in the granite basement of the Cuu Long Basin, Vietnam, and the granite and rhyolite-metarhyolite basement of Osage County, Oklahoma, USA. Cuu Long forms an important unconventional reservoir. In Osage County, we suspect basement control of shallower fractures in the Mississippi chat deposits.

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