NMR in well logging and hydrocarbon exploration

Abstract

Nuclear magnetic resonance (NMR) has become a versatile tool for the evaluation of underground hydrocarbon reservoirs. Formation attributes such as rock porosity and rock pore size distributions, as well as the relative concentrations of water, oil and gas, can be inferred from subsurface NMR. The hydrogen NMR signal encodes porosity as amplitude, pore sizes as relaxation times and fluid properties asa mixture of relaxation and diffusion rates. The paper describes the basic operating principles for NMR on cable (wireline), NMR on a drill string (logging-while-drilling) and NMR for downhole fluid sampling. The geometry of the borehole requires a magnet that projects its field into the surrounding rock, implying a grossly inhomogeneous field distribution. Experience shows that even under these circumstances, saturation-recovery and Carr-Purcell-Meiboom-Gill sequences can work well and yield meaningful T~ and T 2 information.

In vivo assessment of aged human skin with a unilateral NMR scanner

“…They are significantly less expensive than common MRI scanners, can be highly accessible for clinical skin applications and need not be limited to large medical centers. Such scanners, with a small and open permanent magnet, are mainly used today for nondestructive testing and for the characterization of materials and soils . A few major drawbacks severely limit the potential implementation of stray field scanners for medical applications: the small penetration depth prevents their use for organs that are not near the surface, which is not the case for skin; the low and inhomogeneous magnetic field ( B 0 ) dictates low sensitivity ; and, finally, slice‐selective planar imaging is inapplicable, as it demands overly long imaging durations .…”

Spin-Noise Gradient Echoes

“…Also, the simultaneous determination of transverse relaxation rates and diffusion coefficients is attractive for mixture characterization in porous media. Additionally, in situ oil well exploration, (Prammer, 2004) or other applications of NMR in confined spaces would profit from the miniaturization and simplification possible by a detection-only electronic setup. However, the first implementations of the SNGE have also revealed constraints provided by the hardware and the range of experimental systems, which can be studied.…”

NMR in the environmental industry

“…NMR well logging uses an NMR instrument that can be lowered down boreholes several hundreds of metres deep into the Earth's subsurface. [1] In general, an NMR well-logging instrument is constructed with an ex situ magnetic field such that the sample to be analyzed, which in this case is the fluid found within geological materials, lies some short distance (up to a few centimetres) away from the instrument. With current technology, the magnetic field heterogeneities inherent in natural geological formations preclude the acquisition of chemical shift information.…”

“…Perhaps the most prominent forays of NMR into the environmental industry are NMR well‐logging tools and techniques for hydrogeological profiling, which were initially developed and established primarily for oil and gas exploration. NMR well logging uses an NMR instrument that can be lowered down boreholes several hundreds of metres deep into the Earth's subsurface . In general, an NMR well‐logging instrument is constructed with an ex situ magnetic field such that the sample to be analyzed, which in this case is the fluid found within geological materials, lies some short distance (up to a few centimetres) away from the instrument.…”