Nuclear Magnetic Resonance Characterization of Petrophysical Properties in Tight Sandstone Reservoirs

Abstract

Permeability and bound water saturation (Swb) are key parameters reflecting the petrophysical properties of porous rocks. Nuclear magnetic resonance (NMR) has proved to be effective in investigating the properties of porous media. However, estimating Swb and the permeability in tight sandstone reservoirs based on conventional NMR methods, which requires the inversion of NMR echo data to obtain the transverse relaxation time (T2) distribution, proves to be a challenging task. In this study, a method is proposed to estimate Swb and the permeability in tight sandstone reservoirs based on the direct analysis of NMR echo data, thus avoiding the inversion process. A total of 20 tight sandstone samples from the Ordos Basin in China was taken for laboratory NMR measurements. The kernel function of the echo data was used to characterize the ratio distribution of bound water volume to pore volume for different pore sizes. Following this, an echo data calibration method was applied to estimate Swb without the inversion of the T2 distribution, and the window method was used to reduce the impact of noise in the echo data. Furthermore, models for estimating permeability were proposed based on the determined windows of the NMR echo data in the Swb estimation. The reliability of the proposed method for estimating Swb and permeability was verified by comparing the estimated and experimental results. Our study provides an efficient method for the estimation of petrophysical parameters in porous rocks based on the direct analysis of NMR echo data.

Novel Method for Determining Irreducible Water Saturation in a Tight Sandstone Reservoir Based on the Nuclear Magnetic Resonance T2 Distribution

“…The irreducible water saturation of 26 cores was determined by eq based on the decompositions of the T 2 distribution. The results from the proposed method, the integral transformation (IT) method, and the single T 2 cutoff method were compared, as shown in Figure . From Figure , the irreducible water saturation determined by the proposed method and the IT method consists of the measured irreducible water saturation.…”

“…The effect of pore connectivity on irreducible water saturation is taken into consideration in the film model, where the irreducible water exists in both small and large pores. ,− Chen et al estimated the generic coefficients of the irreducible water saturation distribution function derived from the T 2 cutoff value, and the generic coefficients, characterizing the shape of the irreducible water distribution function, can be used to determine the irreducible water saturation. Lu et al explained that the simple cutoff value of the pore radius cannot distinguish irreducible water and movable water at a certain capillary pressure.…”

“…Li et al considered that, when the centrifugal force does not reach the capillary pressure of the fine throat, the water in the macropores, connected with the fine throat, could not be displaced and the relaxation signals would be retained in the macropores of the T 2 distribution after centrifugation. Jin et al extracted the parameters of NMR echo data and calibrated the kernel function with the core experimental results for calculating the irreducible water saturation. The method has good applications for cores, but it has not been applied to tight sandstone reservoirs.…”

Fluid Transport Mechanisms in Unconventional Tight Rocks Based on NMR Imaging

“…11 In addition, NMR has proved to be effective in studying bound water saturation and permeability in tight sandstones. 12,13 Additional advances also include application of downhole NMR tools to estimate fluid type and saturation using T 1 −T 2 mapping 14 and estimation of pore-size distributions and reservoir permeability. 15 imaging of fluids in tight rock samples with short relaxation times using SPRITE sequences 16 as well as direct imaging of fluid flow.…”

Characteristics of movable fluids in tight sandstone reservoir and its influencing factors: a case study of Chang 7 reservoir in the Southwestern of Ordos Basin

“…The main controlling factors that contribute to the obviously different occurrence characteristics of movable fluids are demonstrated to be pore type, pore-throat radius, porethroat radius ratio, sorting coefficient, effective pore-throat volume, and clay mineral filling. Jin et al (2020Jin et al ( , 2021 analyzed the nuclear magnetic resonance characterization of petrophysical properties in tight sandstone reservoirs and then proposed a method for the continuous and quantitative characterization of bound and movable fluid microdistribution in porous rocks based on nuclear magnetic resonance (NMR) measurements.…”