Accurate phase-shift velocimetry in rock

Matsyendra Nath Shukla,Antoine Vallatos,Vernon R Phoenix,William M Holmes

doi:10.1016/j.jmr.2016.04.006

Matsyendra Nath Shukla, Antoine Vallatos + Show 2 more

Open Access

https://doi.org/10.1016/j.jmr.2016.04.006

Copy DOI

Abstract

Spatially resolved Pulsed Field Gradient (PFG) velocimetry techniques can provide precious information concerning flow through opaque systems, including rocks. This velocimetry data is used to enhance flow models in a wide range of systems, from oil behaviour in reservoir rocks to contaminant transport in aquifers. Phase-shift velocimetry is the fastest way to produce velocity maps but critical issues have been reported when studying flow through rocks and porous media, leading to inaccurate results. Combining PFG measurements for flow through Bentheimer sandstone with simulations, we demonstrate that asymmetries in the molecular displacement distributions within each voxel are the main source of phase-shift velocimetry errors. We show that when flow-related average molecular displacements are negligible compared to self-diffusion ones, symmetric displacement distributions can be obtained while phase measurement noise is minimised. We elaborate a complete method for the production of accurate phase-shift velocimetry maps in rocks and low porosity media and demonstrate its validity for a range of flow rates. This development of accurate phase-shift velocimetry now enables more rapid and accurate velocity analysis, potentially helping to inform both industrial applications and theoretical models.

Highlights

Fluid flow through porous media, such as rock or sand packs, is found in a wide range of industrial and natural processes ranging from chemical reactors to petroleum recovery
The Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR) experiment originally proposed by Stejkal and Tanner [5], has long been used to non-invasively study flow and diffusion properties [6]
It is worth noting that the Bentheimer sandstone used in this work is an extremely clean outcrop; far from typical of most rocks types, where extremely short relaxation times, at high magnetic field, can prevent the use of conventional MRI pulse sequences

Summary

Introduction

Fluid flow through porous media, such as rock or sand packs, is found in a wide range of industrial and natural processes ranging from chemical reactors to petroleum recovery. Knowledge of the flow properties in these media can be crucial in understanding transport processes and developing accurate transport models. Nuclear magnetic resonance based approaches enable the complexity of local flow processes within the system to be characterized, moving our understanding of flow beyond bulk average macroscopic descriptions. NMR based approaches have been used to, for example, explore simultaneous flow of oil and water in sandstone [1], unpick complexities in nanoparticle transport behaviour in rock [2], map organic pollutant transport in fractures [3] and image heavy metal removal in bio-film mediated ion exchangers [4].

Methods

Results

Conclusion