Petrology and diagenesis of the lower Mississippian Price Formation, southwestern Virginia

Abstract

The primary objective of this study of four cores from the Lower Mississippian Price Formation was to determine the dominant controls on diagenesis and porosity as the Price sandstones are potential reservoirs for coalbed methane. Facies analyses of the cores, in combination with outcrop data from previous studies, lead to the conclusions that these rocks represent distal bar and prodelta, wave-reworked distributary mouth bar, and upper delta plain deposits. Petrographically, the sandstones typically are fine-grained lithic arenites that were derived from a low-grade metamorphic provenance with lesser sedimentary and minor plutonic influences. Diagenetically, most sandstones are dominated by siliceous cements and replacements, although some samples from the marine zones are dominated by carbonate cements. No original porosity is preserved and secondary porosity of any type is rare, but where present is usually the result of dissolution of carbonate phases. The age of the rocks and the maximum temperature of diagenesis (found to be >150°C throughout these sections) were strongly influential in diagenesis. The composition of the sediments was also very important in compaction, cementation, replacement, and dissolution. The variation in detrital mineralogy is limited, and this, in combination with temperature and age, results in diagenesis that is relatively homogeneous throughout these sections of the Price Formation. Finally, as porosity in the sandstones is extremely low, it seems highly unlikely that the Price Formation sandstones in this area could be economic producers of methane.