Sequence-stratigraphic analysis using well cuttings, Mississippian Greenbrier Group, West Virginia

Abstract

Well-cuttings analysis predates modern carbonate facies analysis, sequence stratigraphy, seismic reflection surveys, and advanced geophysical logging techniques. These newer methods have resulted in well cuttings becoming less important as a major source of data for high-resolution subsurface analysis. Binocular analysis of well-indurated Paleozoic well cuttings can be used to construct detailed vertical facies successions in wells when tied to wire-line logs. Facies analysis can then be used to construct higher resolution sequence-stratigraphic frameworks and time-slice maps. This approach was tested on Mississippian carbonates in the Appalachian Basin of West Virginia. The analysis was done using the washed coarse fraction (1–2 mm; 0.04–0.08 in.) of the cuttings for each sample interval, classified according to Dunham rock type, counted to determine relative abundance, and plotted as percent lithology versus depth for each well. Digitized wire-line logs and the cuttings-percent logs were adjusted (typically 10 ft [3 m] or so) to consider drilling lag, lithologic columns were produced from the combined data, and sequences were picked. Gamma-ray markers were used to correlate the sections, and sequence-stratigraphic cross sections were produced. Time-slice maps were generated that show the thickness of the individual sequences and the distribution of major facies within systems tracts. This approach generated a rock-based, high-resolution sequence framework for the reservoir and led to a much better understanding of controls on the distribution and stacking of reservoirs.