Scaled Physical Modeling of Cyclic CO2 Injection in Unconsolidated Heavy Oil Reservoirs Using Geotechnical Centrifuge and Additive Manufacturing Technologies

Abstract The success of CO2 injection in shallow reservoirs such as CHOPS (Cold Heavy Oil Production with Sands) entails an understanding of the complex interplay of mechanics of gaseous solvent interaction, reservoir deformation, and borehole collapse. This paper provides the design of a highly-instrumented scaled laboratory experiment inside a 2-meter radius beam geotechnical centrifuge, capable of simulating the cyclic CO2 injection into an unconsolidated sandstone specimen at reservoir conditions. Given that sand production during CHOPS creates high-permeability channel-like structures, additive manufacturing technology (i.e. 3D printing with actual sand particles) was used to fabricate the physical model specimen of a scaled reservoir. A centrifuge cell was designed and constructed to simulate the multi-phase cyclic CO2 injection process at the reservoir scale. Scaling factors for stress, time, height and density were used to determine the centrifuge operation. A loading system was included in the centrifuge cell to emulate the vertical stress from the overburden rocks at the top of a shale caprock layer. Stress anisotropy in horizontal stresses were applied through an 8-arm horizontal loading system, similar to a true triaxial cell. A sand trap and a production unit were used to collect the collapsed sands and the produced fluids. To establish residual water saturation, the reservoir prototype was first saturated with water, followed by dead canola oil and live oil (prepared by dissolving CO2). The experiment was started by spinning the 500 kg setup inside the geotechnical centrifuge until it reached a steady rotational speed of 120 revolutions per minute (equivalent to 30 times the gravitational acceleration). The perforations of a scaled wellbore within the reservoir prototype were opened to initiate fluid and sand production. It appeared that the increase in the cohesion of the 3D printed rock in regions away from wellbore reduced rock failure during production cycles even with large seepage forces and pressure gradients. The structural changes around high-permeability zone and near-wellbore region were related to stress concentration. The result of our scaled physical experiments delivers insights on fluid displacement and rock deformation during CO2 saturated oil production from a reservoir prototype. The application of a geotechnical centrifuge and additive manufacturing technology provides a platform to experimentally explore the multi-scale, multi-physics processes of sampling, flow, and deformation issues observed in subsurface systems including H2 storage and safe disposal of radioactive waste.