Formation of Diagenetic Alteration Zones by Leaking Reservoir Hydrocarbons over Three Oil Fields in Oklahoma: ABSTRACT

Abstract

Examination of rotary-drill well cuttings from 105 wells within and adjacent to the Eola, Velma, and Chickasha oil fields in southern Oklahoma has revealed diagenetic mineral zonations within Permian sandstones overlying the fields. Permian sandstones which are usually red on outcrop are altered to white over the fields, owing to a change in cementing materials from limonite, hematite, and carbonates to ferroan calcite, ferroan dolomite, and, in some places, pyrite. Bleaching and mineralization were restricted to sandstones and were brought about by the reduction of iron oxides by hydrogen sulfide associated with petroleum and/or generated by a reaction between hydrocarbons and sulfate ions. Hydrogen sulfide reacted with iron oxide to form pyrite, and with oxygen in groun water to form sulfur. Pyrite cement occurs in zones that overlie pre-Permian faults, oil productive areas, and zones that are elongated along structural trends. Zone boundaries are nearly vertical and extend to the surface. Average pyrite content of mineralized sandstone is 3%. Pyrite occurrences show that petroleum-bearing fluids were introduced into Permian rocks by vertical movement along high-angle normal and reverse faults that cut reservoirs at depth and that intersect unconformities at the base of the Permian section. End_of_Article - Last_Page 924------------