Reservoir Simulation of Tracer Transport in Multicomponent Multiphase Compositional Flow with Applications to the Cranfield CO2 Sequestration Site

Abstract

Reservoir simulators are widely used to constrain uncertainty in the petrophysical properties of subsurface formations by matching the history of injection and production data. However, such measurements may be insufficient to uniquely characterize a reservoir's properties. Monitoring of natural (isotopic) and introduced tracers is a developing technology to further interrogate the subsurface for applications such as enhanced oil recovery and CO2 sequestration. Oak Ridge National Laboratory has been piloting this technology during and following three CO2 injection campaigns at the Cranfield, Mississippi, CO2 sequestration test site. Multiple perfluorocarbon tracers and isotopes were injected together with CO2 and monitored at two wells at 68 m and 112 m from the injection site. Surprisingly, tracer breakthrough at both monitoring wells occurred at nearly the same time, and was not significantly affected when the CO2 injection rate was nearly doubled. Multiple tracer peaks were also observed after breakthrough. These observations suggest that the CO2 plume did not expand radially, but that multiple flow paths developed towards the monitoring wells. This is indicative of either channeling through high permeability pathways or of fingering. The results demonstrate that tracers provide an important complement to transient pressure data.

To aid the development of this new technology, we enhanced a fully compositional multiphase reservoir simulator to interpret inert tracer transport. Our research simulator uses higher-order finite element methods that can capture the small-scale onset of fingering on the coarse grids required for field-scale modeling, and allows for unstructured grids and anisotropic heterogeneous permeability fields. Mass transfer between fluid phases and phase behavior are modeled with rigorous equation-of-state based phase-split calculations. We present our tracer simulator and preliminary results related to the Cranfield tracer experiments.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016