Relationships Among Thermal Maturity, Sandstone Diagenesis, and Reservoir Quality in Pennsylvanian Strata of the Arkoma Basin

David W. Houseknecht, Lori A. Hathon

Relationships among elevated thermal maturity, sandstone diagenesis, and reservoir quality have been examined in Atokan and Desmoinesian strata of the Arkoma basin that are characterized by vitrinite reflectance values ranging from less than 1 to more than 5%. Good reservoir quality and significant gas reserves exist in patterns that do not appear to be influenced by either lateral or vertical thermal maturity trends.

In most sandstones, diagenetic processes that occurred during shallow burial exerted a significant influence on reservoir quality. For example, the presence of early chlorite grain coatings, the occurrence of which is largely facies dependent, helped preserve reservoir quality by inhibiting precipitation of quartz cement. In sandstones lacking chlorite grain coatings, quartz cementation destroyed most porosity prior to the generation of hydrocarbons.

During deeper burial, accumulation of hydrocarbons in porous sandstones located in favorable structural positions effectively terminated inorganic diagenesis and prevented further deterioration of reservoir quality. However, intergranular pressure solution and quartz cementation proceeded below hydrocarbon-water contacts. This postaccumulation diagenesis occurred during or following metagenesis as evidenced by cement filling bubbles and cracks in pyrobitumen. Thus, good reservoir quality was maintained because of the presence of hydrocarbons, even though they were being thermally degraded during continued maturation. These results indicate that sandstone reservoir quality and significant gas reserves can be preserved to extreme levels of thermal maturity (R_o > 5%) if accumulation predates overmaturation. However, sandstones in positions unfavorable for accumulation experience total destruction of reservoir quality as a result of high-temperature diagenesis.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.