Evaluating avulsion controls on fluvial sand body architecture and connectivity

Open Access
Author:
Baisden, Tramond Rashard
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 24, 2015
Committee Members:
  • Elizabeth Ann Hajek, Thesis Advisor
  • Demian Saffer, Thesis Advisor
  • Rudy Slingerland, Thesis Advisor
Keywords:
  • geology
  • fluvial
  • connectivity
  • petroleum geology
  • sedimentary geology
  • reservoir modelling
  • wasatch
  • lidar
  • avulsion
Abstract:
Various scales of heterogeneity affect fluvial reservoir performance and are typically difficult to predict. Channel-belt-scale heterogeneity results from fluvial processes such as bar migration and reworking, and avulsion processes which build multi-story sand bodies (MSBs). Depending on basin conditions and avulsion patterns, channel belts may stack vertically or laterally, with each potentially affecting reservoir area and connectivity. The well-exposed Wasatch Formation (Paleocene/Eocene, Piceance Basin, Colorado, USA) exhibits three distinct styles of fluvial sand bodies and serves as the study area for this work. Using LiDAR and panoramic photo panels, field observations of the internal and external geometry of sand bodies were made and used to construct generalized channel elements for two net-to-gross (high and low) scenarios. Simplified two-dimensional models generate reservoirs ranging from one to five stories. A suite of vertical aggradation rates and model widths develop domains that facilitate both lateral and vertical stacking of channel elements. Maximum connected areas and number of compartments are recorded for each model run. Results suggest high net-to-gross scenarios typically result in higher reservoir areas and lower compartmentalization. As aggradation and model width increase, reservoir area decreases while compartmentalization increases. High quality reservoirs are dominated by vertical stacking for low and high-net scenarios. There exist at least two scenarios where low-net, vertically stacked channels result in better connected, larger reservoirs than high-net, laterally stacked channels.