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Understanding Nuclear Magnetic Resonance Imaging Technology for Displacement Devices

Shenjia Hydraulics

Release Date:

2023-02-03

Polymer flooding is an enhanced oil recovery technique that injects polymer into the reservoir to displace oil. At the macroscopic scale, it primarily works by increasing the viscosity of the displacing fluid and reducing the mobility ratio between the displacing and displaced fluids, thereby expanding the swept volume. At the microscopic scale, due to its intrinsic viscoelasticity, the polymer can stretch oil films or droplets during flow, enhancing their transport capacity and improving microscale oil‑displacement efficiency.

Polymer flooding is an enhanced oil recovery technique that injects polymer into the reservoir to displace oil. At the macro scale, it primarily works by increasing the viscosity of the displacing fluid and reducing the mobility ratio between the displacing and displaced fluids, thereby expanding the swept volume. At the micro scale, the polymer’s inherent viscoelasticity enables it to stretch oil films or droplets during flow, enhancing its carrying capacity and improving microscopic sweep efficiency.

Displacement device

　　As is well known, polymer flooding demonstrates superior oil‑recovery performance in heterogeneous reservoirs compared to homogeneous ones, and since most real‑world reservoirs exhibit varying degrees of heterogeneity, investigating polymer‑flood processes in heterogeneous formations is more practical. However, with conventional experimental approaches, the representative reservoir model essentially functions as a “black box,” requiring analysts to infer the oil‑saturation profile solely from monitored injection and production rates and pressures. Such experimental methods clearly impose significant limitations on the study of polymer flooding in heterogeneous reservoirs.

　　Core displacement experiments are the established method for studying fluid flow within rock cores. Traditional core‑flow tests typically treat the actual reservoir model as a “black box,” relying solely on measurements of macroscopic parameters such as inlet and outlet pressures, confining pressure, flow rate, and electrical resistivity. While these data can be used to infer gel mobility and displacement efficiency in the core, they fail to reveal the gel’s migration pathways or the detailed distribution of fluids. With the rapid advancement of modern high‑tech technologies, nondestructive testing has found widespread application in petroleum exploration and production. Nuclear magnetic resonance (NMR) is a powerful tool for investigating the internal structure and seepage characteristics of porous materials. It enables rapid, nondestructive visualization of subsurface rock architecture and real‑time monitoring of fluid invasion, permeation, and displacement processes, thereby facilitating timely assessment of the gel’s true flow distribution within the core and the effectiveness of profile control and displacement during the displacement operation.

　　Core Displacement Visualization System for Displacement Devices

　　With the advancement of water‑flood development, most oilfields in China have entered a “double‑high” stage characterized by high water saturation and high recovery rates. For the swept zones and residual oil remaining in these swept zones—areas that cannot be recovered through secondary recovery—it is particularly crucial to understand that such residual oil provides an essential foundation for both tertiary recovery and enhanced oil recovery efforts.

　　Residual oil distribution refers to the spatial distribution of residual oil within a reservoir. Numerous factors influence this distribution, primarily the static characteristics of the reservoir and the dynamic injection–production conditions. The static reservoir attributes constitute the fundamental, intrinsic factors, while the injection–production regime represents the extrinsic factors that shape residual oil distribution.

　　Nuclear Magnetic Resonance Principle of Core Flooding in Displacement Devices

　　Nuclear magnetic resonance, with its exceptional ability to detect hydrogen signals, plays a crucial role in the study of oil and gas reservoirs. By employing multi-field coupling accessories, it is possible to simulate the true high‑temperature, high‑pressure conditions found in subsurface formations. In NMR T2 spectroscopy, the relaxation times of oil and water signals vary among cores with different pore sizes. Through displacement experiments, the NMR T2 spectrum evolves in response to changes in the oil–water phase distribution within the core, enabling quantitative analysis of the reservoir’s oil and gas production process. Moreover, leveraging the capabilities of nuclear magnetic resonance imaging, it is possible to visualize each stage of the entire displacement process, providing a clear depiction of dynamic changes and achieving visualization of oil–water mobility during displacement. Core displacement visualization system.

　　The high-temperature core displacement visualization system can be integrated with conventional peripheral displacement setups to simulate the high‑temperature, high‑pressure conditions of reservoirs, enabling full‑process, visualized displacement studies on core samples. Visualization allows for qualitative assessment of core displacement behavior, while changes in spectral profiles facilitate quantitative calculation of displacement volumes. Nondestructive core sectioning and layer selection can be performed at any depth and from multiple viewing angles.