Potential for Subthrust Gas Fields: Results of Recent Deep Drilling in the Ouachitas: ABSTRACT

Abstract

The Broken Bow anticline, with dip closure of over 170 mi/sup 2/, is the Oklahoma culmination of a long regional trend extending from Arkansas to central Texas. The Standard Oil 1-22 Weyerhaeuser well, drilled to 18,980 ft, is the first crestal well on this feature to rest the subthrust section beneath the Ouachita fold and thrust belt. The wellspudded in and drilled a substantial section of sloates, phyllites, and calcareous quartzites of presumed Ordovician and Cambrian(.) age. The basal Ouachita thrust was penetrated at 11,714 ft, where an interpreted Ordovician Simpson-Arbuckle section was encountered. Reflectance methods using pyrobitumen and visual determination of metamorphic grade indicated the presence of a significant maturity reversal at the thrust boundary. Although economic quantities of hydrocarbons were not found in this well, the following observations may influence future work. (1) A para-autochthonous section of shelf carbonates and sands exists in the subthrust, at least 60 mi from the leading edge of the Ouachita thrust belt. (2) The abundance of pyrobitumen observed in the Simpson section suggests the former presence of significant hydrocarbons. (3) The well encountered good dolomite reservoir at high maturities (R/sub 0/ = 7-8%) that flowed formation water and unexpectedly contained dissolved C/sub more » 1/ to C/sub 3/. These observations suggest that high maturities alone may not be a condemning factor and should be considered in future exploration plays. « less