Application of NMRT₂to Pore Size Distribution and Movable Fluid Distribution in Tight Sandstones

Abstract

This paper explores the applicability of nuclear magnetic resonance (NMR) technology on pore size distribution (PSD) and movable fluid distribution (MFD) in tight sandstones. Centrifugation experiments and NMR tests are performed on saturated samples. The fluid changes in pores corresponding with three different types of NMR T 2 distribution after each centrifugation is then analyzed. In addition, a new method to determine the conversion factor from NMR T 2 distribution to PSD is developed. In comparison with the PSD obtained by mercury intrusion porosimetry, the new method is more suitable for PSD calculation in tight sandstones. Afterward, the optimum centrifugal force to determine the threshold radius for fluid flow is obtained. On the basis of this, we analyze MFD in tight formation. Through study, the following results are arrived at: patterns of NMR T 2 distributions of outcrop and subsurface cores at water saturation condition can be classified into three types (I, II, and III). Among which, type I and type II show a better pore connectivity than type III with NMR T 2 distribution of a higher movable peak and a lower immovable peak. The optimum centrifugal force for the Chang 6 tight formation to determine movable fluid is 418 psi and pores show no obvious difference with throats when radii are less than 0.05 μm. Movable fluids are mostly controlled by throats with radii smaller than 1 μm, especially throats with radii between 0.3 and 1 μm. Movable fluids are mostly stored in pores around the movable peak of bimodal NMR T 2 distribution with radii ranging from 10 to 100 μm. These pores are residual interparticle pores and dissolution pores. The sets of experiments and the new method presented in this paper are proved effective in quantitively describing PSD and also qualitatively evaluating pore throat connectivity in tight sandstones. Petrophysical characterization by NMR technique provides an effective approach to better understand pore throat structures and storage capacity of tight oil reservoirs.

A comparative study of the nanopore structure characteristics of coals and Longmaxi shales in China

“…Similar experimental methods are used in the pore structure characterization of coal and shale gas reservoirs, which primarily consist of fluid injection and noninvasive imaging methods. The fluid injection method includes low‐pressure nitrogen gas adsorption (LP‐N 2 GA), low‐pressure carbon dioxide gas adsorption (LP‐CO 2 GA), high‐pressure mercury injection (HPMI), and low‐field nuclear magnetic resonance (LF‐NMR) . The noninvasive imaging method includes micro‐ and nano‐CT, scanning electron microscope (SEM), focused ion beam scanning electron microscope (FIB‐SEM), and small‐angle neutron scattering (SANS) .…”

Waterflooding Huff-n-puff in Tight Oil Cores Using Online Nuclear Magnetic Resonance

“…The NMR T 2 distribution of the cores saturated with simulated formation water was converted into pore radius distribution [43,45,46]. The NMR data obtained from the cores saturated with simulated formation water were converted into pore radius distribution.…”

“…Usually, the core NMR test method is used to measure the transverse relaxation time T 2 , which is the time from the hydrogen proton running out of the equilibrium state laterally until the equilibrium state is restored. The amplitude distribution corresponding to the relaxation time T 2 reflects the size of the specific surface in the rock pores and the strength of the molecular action on their inner surface [40,42,43]. The relaxation time of a hydrogen nucleus in each rock pore can be expressed by the following equation:…”

Quantitative Characterization of Pore Connectivity and Movable Fluid Distribution of Tight Sandstones: A Case Study of the Upper Triassic Chang 7 Member, Yanchang Formation in Ordos Basin, China

“…Nuclear magnetic resonance (NMR) nondestructively analyzes pore characteristics and the fluid distribution of samples, based on correlations between the movement of hydrogen atoms in water or hydrocarbon fluids and pores in rocks [37]. This experiment was carried out on a MacroMR12-150H-I NMR instrument produced by Newman, with the maximum number of echoes in the CMPG being 18,000 and the shortest echo time being less than 420 μs.…”