Flow visualization of CO2 in tight shale formations at reservoir conditions

Abstract

The flow of CO2 in porous media is fundamental to many engineering applications and geophysical processes. Yet detailed CO2 flow visualization remains challenging. We address this problem via positron emission tomography using 11C nuclides and apply it to tight formations - a difficult but relevant rock type to investigate. The results represent an important technical advancement for visualization and quantification of flow properties in ultratight rocks and allowed us to observe that local rock structure in a layered, reservoir shale (K-=-0.74-μdarcy) sample dictated the CO2 flow path by the presence of high-density layers. Diffusive transport of CO2 in a fractured sample (high-permeable sandstone) was also visualized, and an effective diffusion coefficient (Di-=-2.2-·-10-8-m2/s) was derived directly from the dynamic distribution of CO2. During CO2 injection tests for oil recovery from a reservoir shale sample we observed a recovery factor of RF-=-55% of oil in place without fracturing the sample.