Monitoring Shale Water Uptake Using 2D Magnetic Resonance Relaxation Correlation and SPRITE MRI

Abstract

Fluid storage and transport in shale and clay formations is important in many areas of application, including hydrocarbon recovery from, and waste fluid storing in, these reservoirs. The multiscale heterogeneous nature of shales is largely responsible for these rocks being considered unconventional and complicated. Researchers often rely on imaging methods to provide spatial information to characterize their heterogeneity. SEM and nano-CT are powerful methods that have been used to give images of shale nanopores with fields of view (FOV) of 100 μm. However, this limited FOV has raised questions about the validity of simulations based on these methods to scale up and represent macroscopic shale properties. Here, we have used, for the first time, SPRITE Magnetic Resonance Imaging (MRI) methods to give core plug size shale images. The imaging method resolves water and oil signals to give separate images of each in shales. “As received” shale samples were used to acquire 1D and 3D oil and water images to characterize natural fluid distribution. Water uptake experiments were conducted to probe fluid displacement in shales. Measurements included gravimetric, Magnetic Resonance (MR) T1-T2* relaxation correlation, and SPRITE imaging methods. Water and oil images showed that sample scale heterogeneities are imposed by the shale beddings. Water uptake experiments (1) showed the capability of the T1-T2* method to identify MR signals from shale fracture water and matrix pore water, and (2) illustrated wettability control of spatial water distribution in shales during spontaneous imbibition.