Negative Flower Structure in the Mississippian Lime: Evidence of Secondary Porosity and a Possible Play Concept

Abstract

Fault/fracture related “hydrothermal” carbonate reservoirs are important in many sedimentary basins. Examples include Albion-Scipio (Michigan), Ladyfern (British Columbia), Deep Panuke (offshore Nova Scotia) and possibly the giant Ghawar field in Saudi Arabia. In these reservoirs secondary porosity is developed through brecciation, dolomitization and hydrothermal leaching by warm (~60°-150°C) basinal brines. Similar secondary porosity also is common in Mississippi Valley-type (MVT) base metal deposits. Here, we show that the Mississippian Lime play of the southern Midcontinent of North America may also contain pockets of secondary porosity developed though the same mechanism. These same Mississippian age rocks host the world-class Tri-State MVT mineral district at the boundary of Oklahoma, Kansas and Missouri where the ore deposits are fault and fracture controlled and the host rocks are heavily brecciated with evidence of “hydrothermal” leaching. In addition to the metal-sulfide ores, rocks in the Tri-State district also contain large volumes of liquid petroleum. In a 3D seismic volume from Payne County, OK, located 230km to the SW of the Tri-State district, a “sag” was observed in the Mississippian Lime unit. This feature is fully enclosed by normal faults with a left-lateral strike-slip component and forms a classic negative flower structure. The bounding fault with the larger throw appears to originate from the basement. The faults bounding this structure, along with other faults in the region, could act as conduits for vertical fluid migration from deeper in the Anadarko basin. In such settings hydrothermal fluids may enhance porosity through brecciation and leaching, in a manner similar to the Tri-State mineral district, resulting in a net porosity increase. Ongoing regional fluid inclusion and stable isotope analyses strongly indicates that basinal fluids may indeed have affected the Mississippian age limestones. The flower structure interpreted in the seismic volume could be a potential play. Play concepts, such as that presented in this paper, are critical to the ongoing search of hydrocarbons in the unconventional Mississippian Lime resource play.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015