Role of Diagenesis in Development of Upper Morrow Fan-Delta Reservoirs in Anadarko Basin

Zuhair Al-Shaieb, Patricia L. Alberta, Mike Gaskins

Upper Morrow chert conglomerates are prolific natural gas reservoirs in the deeper part of the Anadarko basin. Based on the data obtained during the course of this investigation, the conglomerates display several diagnostic features of a fan-delta depositional environment, with various facies representative of mid-fan and distal parts of the delta-fan complex. These facies were calibrated to suites of wireline logs, characteristic log signatures were identified for each facies, and a map was prepared showing the distribution of facies within the fan-delta complex. Major lithology types of conglomerates are chert, quartz, and feldspars, and a combination of these three constituents.

A rather complex diagenetic history includes at least nine cementation episodes reflecting various subsidence stages and thermal regimes.

Reservoir-quality lithofacies are present mainly in the mid-fan channel facies, which consists of stacks and repetitive sequences of braided-stream deposits. Both intergranular primary and secondary porosity types are present in the chert conglomerates. Although intergranular porosity is very common, it was modified by cementation and dissolution. Complete preservation of original porosity is rare. Remnant primary porosity has provided avenues for fluid migration, which resulted in partial to complete dissolution of rock constituents. Siliceous detrital matrix, chert, and feldspar are the major constituents affected by the dissolution processes. A geochemical model emphasizing the role of feldspar hydrolysis is proposed to explain the dissolution of chert and development of productive reservoirs in the chert conglomerates.

AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.