InterPore2021

Dynamics of Water and Gas Injection in an Oil-Wet Reservoir Rock at subsurface conditions: A Pore-Scale Synchrotron X-ray Imaging Study

2 Jun 2021, 14:00

15m

Oral Presentation (MS6-A) Physics of multi-phase flow in diverse porous media MS6-A

Speaker

Abdulla Alhosani (Imperial College London)

Description

Understanding the pore-scale fluid dynamics occurring during multiphase flow in porous media is important for the design of many applications including subsurface carbon dioxide storage, microfluidic devices, membrane fuel cells, and packed bed chemical reactors. To investigate the displacement dynamics of two- and three-phase flow in a hydrophobic porous medium, we use synchrotron X-ray microtomography to image the flow of water and gas in an oil-wet reservoir rock at high pressure and temperature (8 MPa and 60 oC).
After altering the wettability of the rock surface, towards oil-wet conditions, in a process known as ageing, water is injected at a very low flow rate (0.15 µL/min) in the oil-filled rock which is simultaneously imaged every 70 s to track the advance of the water front. Gas is then injected in the system at the same flow rate and images are acquired every 74 s. The use of fast synchrotron imaging with a high spatial resolution (3.5 µm) allows us to examine, in situ, (i) wettability and displacement contact angles, (ii) invasion patterns (pore-filling order), (iii) displacement events, (iv) fluid connectivity, and (v) change in Minkowski functionals – fluid saturations, specific interfacial areas, and curvatures.
During water injection, the displacement of oil by water is a drainage-like process, where water advances as a connected front displacing oil in the center of the pores, confining the oil to wetting layers. The displacement is an invasion percolation process, where throats, fill in order of size, with the largest available throats filled first, indicating that the displacement in our heterogeneous rock is predominantly size controlled. Furthermore, we observe drainage associated pore-filling dynamics including Haines jumps and snap-off events during water injection. Haines jumps occur on single- and/or multiple-pore levels accompanied by the rearrangement of water in the pore space to allow the fast filling. Snap-off events are observed both locally and distally with trapped water ganglia reconnecting as the water injection proceeds.
During the subsequent gas injection, gas invades the rock in a unique pattern, where it progresses through the pore space in the form of disconnected clusters mediated by double and multiple displacement events. Gas advances in a process we call three-phase Haines jumps, during which gas re-arranges its configuration in the pore space, retracting from some regions to enable the rapid filling of multiple pores. Nevertheless, unlike the two-phase water injection, the gas retraction leads to a permanent disconnection of gas ganglia, which do not reconnect as gas injection proceeds. We observe, in situ, the direct displacement of oil and water by gas as well as gas–oil–water double displacement. The wettability order is oil–gas–water from most to least wetting, indicating that the rock surface is strongly oil-wet. Furthermore, quantifying the evolution of Minkowski functionals implied well-connected oil and water phases, while the gas connectivity decreased as gas was broken up into discrete clusters during injection.