| Description |
The classic view portrays offshore marine, organic-rich mudstone systems as low energy environments dominated by suspension settling sedimentation and oxygen-depleted redox conditions. Recent advances in mudstone sedimentology have shattered this long-standing dogma, leading to a re-evaluation of mudstones successions. The emerging view indicates mud accumulates through a variety of processes and under different energy regimes, viz., mud-dominated systems are highly dynamic environments. The overall aim of this study is to provide a holistic interpretation of heterogeneity in ancient offshore marine mudstone successions to provide more realistic depositional models and robust sequence stratigraphic frameworks. The late Paleozoic Wolfcamp A and D formations in the Delaware and Midland Basins, West Texas, respectively, are used as case studies. Chapter 1 documents and explains the ranges, types, and causes of mudstone heterogeneity and its relationship to changing paleodepositional conditions in the Late Pennsylvanian Wolfcamp D Formation of the Midland Basin. Six microfacies reflecting sedimentation in four unique depositional environments are identified based on detailed core descriptions, thin section petrography, organic geochemistry, and high-resolution elemental data. Building on the results from Chapter 1, Chapter 2 introduces an integrated workflow to identify cycles and define sequence stratigraphic units in mudstones systems. This workflow combines supervised fuzzy c-means (FCM) clustering analysis of major and trace element data with microfacies and depositional environment analysis. Three orders of glacially-driven eustatic cycles are identified in the Wolfcamp D, each associated with a distinct sequence stratigraphic unit. From high to low frequency, these units include parasequences (types 1 and 2), parasequence sets (T-R cycles), and systems tracts (lowstand and highstand systems tracts; LST and HST). Finally, in Chapter 3 the extent of unconventional reservoir homogeneity and directionality is determined for the early Permian Wolfcamp A Formation in the Delaware Basin via spatial statistics. Incremental spatial autocorrelation (ISA), Hot spot analysis (HSA), semivariograms, and semivariogram maps are used to that end. Spatial statistics of key reservoir properties in the Wolfcamp A indicate the maximum reservoir autocorrelation distance is ~3.5 miles. The direction of homogeneity is oriented NE-SW, roughly along paleodepositional strike of an inferred north-to-northwest-sourced siliciclastic subaqueous fan system. |
