| Description |
Nearshore fluvial to tidal transitional depositional systems are becoming increasingly important due to the large number of global hydrocarbon reserves held in such deposits. These deposits are inherently complex due to their heterolithic nature and therefore, interpreting facies and facies relationships in seismic reflection profiles is problematic. The fluvial and tidally influenced nearshore deposits of the late Cretaceous John Henry Member (JHM) of the Straight Cliffs Formation, located in the Kaiparowits Plateau of southern Utah, offers an excellent opportunity to improve our understanding of how the fluvial to tidal transition impacts subsurface petroleum reservoirs and their expression in seismic reflection profiles. The focus of the first chapter is to investigate the impact of heterogeneous depositional environments and their rock properties to model amplitude versus offset (AVO) using a single core. Core EP-25 exhibits lithofacies from a progradational succession, from shoreface through tidal to fluvial. In order to model the most likely lithofacies stacking patterns present in the core, Markov Chain analysis was conducted. Benchtop measurements performed on 1 inch core plugs obtained rock properties (Vp, Vs, density, permeability, and porosity) for each lithofacies. Average rock properties for each lithofacies were used to generate synthetic seismic reflection models of the different upward fining facies associations documented directly from the core, in order to model variations in amplitude versus offset responses as a function of variable tidal influence. The focus of the second chapter is to capture probable 3-dimensional geobody distributions with a particular focus on coal geobody distribution using previously studied cores and outcrops on the plateau. Three different seismic forward models were created ranging in complexity, using cores EP-25, EP-07, density logs, and the nearby outcrop study Left Hand Collet. The rock properties obtained from the benchtop measurements were used to populate the three models based on different depositional environments at the separate depth slices capturing multiple geomorphic rather than stratigraphic models. A seismic survey was acquired on the plateau using 80 Hz frequency; this produced a high-resolution seismic profile. Comparing the forward seismic model to the acquired seismic profile allows for a conceptual understanding between predictive models of what is expected and what is captured in seismic reflection profiles. |
