Impacts of Diverse Fluvial Depositional Environments on Hydraulic Fracture Growth in Tight Gas Reservoirs

Abstract

Summary In an attempt to enhance the understanding of fracture growth in fluvial systems, this paper provides an analysis of the impact of depositional environments and associated heterogeneities on hydraulic fracturing growth in fluvial tight gas reservoirs. A 3D geostatistical reservoir model, representing a 160-acre field area, was created based on a 3D meandering fluvial tight gas geologic model developed from outcrop. This detailed geologic model differentiates between sandstone-dominated channel-belt environments including point bars, crevasse channels, and crevasse splays, as well as the intervening overbank environments consisting of mudstone and coal deposits. Petrophysical properties and reservoir conditions used in the reservoir model were based on subsurface data from nearby producing fields with comparable fluvial systems. Two different well locations were then chosen within the 3D model in an effort to capture various sandstone body distributions. A range of hydraulic fracture orientation planes, associated with the two well locations, were selected and loaded into a 3D hydraulic fracture modeling package. Eight cases, representing various stimulation-treatment sensitivities, were studied. Results show that consideration of both vertical and lateral reservoir changes is critical to understanding fracture growth in fluvial systems. When comparing a layered system with no lateral variation to a system with lateral variation, 1-year cumulative production can vary by as much as 25%. Subtle lithofacies variations, present in significant quantities in these complex depositional systems, affect fracture growth and can affect well production by 25 to 50%. Additionally, how depletion is treated in the fracturing model (i.e., whether the entire interval is considered depleted or just a single sand body) can also have a significant effect on fracture propagation.