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Quantitative Prediction of Sandbody Connectivity within Distributive Fluvial Systems Using Process-Based Numerical Modeling

Abstract

Fluvial deposits constitute a particularly challenging reservoir type due to their complex facies architecture. The primary control of reservoir performance is sandbody connectivity, which is a result of longitudinal, lateral, and temporal channel contacts. Advances in understanding the large-scale spatial distribution of fluvial facies from modern and ancient systems have led to the development of the Distributive Fluvial System (DFS) model. It provides a plan-view framework to predict the distribution of channel stacking patterns depending on location within the DFS (proximal, medial or distal). At present, the model is qualitative and excludes accommodation-driven controls predicted in the Leeder-Allen-Bridge (LAB) model. Quantifying the DFS model through outcrop analogues is difficult due to the limited number of case studies with exposure of the entire system. Flume tank experiments have full exposure and parameter control but introduce significant upscaling uncertainty. Process-based numerical models allow full exposure and parameter control at a range of scales. The Luna DFS out of the Ebro Basin in northwestern Spain was chosen as input for a suite of models. The fluvial parameters were taken from the High Island Creek in Minnesota, USA, a contributary to the Minnesota River. A base model that reproduced the sedimentary architecture of the input system was computed for the Luna DFS. To determine the impact of changing accommodation, sediment supply, and climate on the base cases, a suite of models was created that covers a range of these input parameters. The ranges were derived from literature studies. The process-based numerical software used are deterministic and thus create a single model for each input parameter set. To obtain a statistically sound sensitivity analysis, significant amounts of parameters sets were modelled. Sandbody connectivity analysis was undertaken to quantify the reservoir architecture of the different models. Preliminary results show a reduction in channel width and increase in channel number downstream. Using process-based numerical modelling to analyze the sensitivity of sandbody connectivity to governing parameters will result in a greatly improved understanding and predictability of reservoir connectivity in fluvial systems as a function of environmental and tectonic controls.