Bruce Ainsworth, Principal Reservoir Geoscientist, Chevron
Sequence stratigraphy based on wireline logs, cores and outcrops is entering its fourth decade of mainstream usage in industry and academia. The technique has proved to be an invaluable tool for improving stratigraphic analyses in clastic shallow marine systems. In this talk we will present a simple quantitative technique to support sequence stratigraphic interpretations. The technique, utilizes two pieces of data that are readily available from every subsurface field or outcrop study; 1) parasequence thickness (T) and 2) parasequence sandstone fraction (SF). The key assumptions are that parasequence thickness can be used as a proxy for accommodation at the time of deposition, and parasequence SF can be used as a proxy for sediment supply. This means that quantitative proxies for rates of accommodation development and sediment supply can be acquired from wireline logs, cores and outcrop data. Vertical trends in parasequence thickness divided by SF (T/SF) approximate trends expected in systems tracts for changes in the ratio of rate of accommodation development to rate of sediment supply (δA/δS). The technique, termed “TSF analysis”, can also be applied at lower-order sequence and composite sequence scales. It provides a quantitative and objective methodology for determining rank and order of sequence stratigraphic surfaces and units. Absolute TSF values can be utilized to determine shoreline, stacked shoreline and shelf margin trajectories. Case studies are presented which demonstrate the robustness of the technique across a range of different data sets. Implications and potential future applications of TSF analyses will also be discussed.