Model analysis of CO2 residual trapping from single-well push pull test — Heletz, Residual Trapping Experiment II

Abstract

Residual or capillary trapping is one of the key trapping mechanisms for CO2 geological storage. At the Heletz, Israel, pilot injection site, two dedicated field experiments have been carried out to characterize it in-situ. This paper presents the model analyses of the second of these tests, the Residual Trapping Experiment II (RTE II). In the experiment hydraulic, tracer and thermal tests before and after the generation of the residually trapped zone are used to quantify residual saturation. The creation of the residually trapped zone is based on injection of CO2-saturated-water following injection of free-phase supercritical CO2. For the modeling, both a radial-symmetric model with homogeneous layer properties and 3D model with stochastically heterogeneous properties were used. Extensive parameter sensitivity studies were carried out and various well-geometry related fluid injection/withdrawal scenarios were considered. In terms of the best estimate for the maximum residual saturation, this experiment, like the previous RTE I experiment, gave the best agreement with a residual gas saturation of 0.1, this value being somewhat lower than the core-measured value of 0.2. Overall, the pressure response provided a very robust signal enabling to distinguish different values of residual saturation as well as the extent of sections where gas blocking for water flow could have occurred. Analysis of the tracer data indicated the presence of phenomena such as gas-blocking water flow, the importance of multi-layer and channelized flow and transport, and the importance of taking into account the processes in the actual injection/production well also.