Characterization of Movable Fluid Distribution in Tight Oil Reservoirs by NMR and Centrifugation

Abstract

The reservoir of Chang 7 Member of Yanchang Formation in the Ordos Basin is rich in tight oil resources, with well-developed micro-nanopore throats, strong heterogeneity, and complex fluid distribution characteristics. In this paper, a combination of nuclear magnetic resonance and centrifugation experiments is carried out to qualitatively and quantitatively analyze and evaluate the distribution characteristics of the movable fluid in Chang 7 reservoirs in Baibao Block. With different centrifugal forces, the NMR T2 spectrum characteristics of saturated water state and different centrifugal force state can be obtained, and the movable fluid distribution characteristics under the control of different centrifugal forces and different pore throat intervals can be obtained. The research results demonstrate that the NMR T2 spectrum of the Chang 7 tight oil reservoir in the study area presents a double-peak or triple-peak shape. With the increase of centrifugal force, the water saturation value of the corresponding sample gradually decreases. The overall movable fluid saturation ranged from 19.07% to 32.52%, with an average of 26.23% and a low degree of movability. The submicron (0.1~1 μm) and nanoscale (0.075~0.1 μm) pore throats were the main pore throat intervals controlling the movable fluid saturation of the studied samples, accounting for an average of 18.31% and 5.57%, respectively, and micron-scale pore throats ( r > 1 μ m ) accounted for an average of 2.35% of the movable fluid distribution.

Fluid Identification Method of Nuclear Magnetic Resonance and Array Acoustic Logging for Complex Oil and Water Layers in Tight Sandstone Reservoir

“…However, since the nuclear magnetic T 2 spectrum is easily affected by pore structure, fluid distribution in micropores, and fluid types, some logging interpretation methods developed based on NMR logging are not applicable in tight reservoirs [19,20]. Although the two-dimensional NMR logging includes more comprehensive information and has more advantages in fluid identification of tight sandstone reservoirs than one-dimensional NMR logging, it has not been widely used in many oilfields because of its high price and complex data processing process [21][22][23]. In terms of fluid identification by array acoustic logging, array acoustic logging can directly measure the P-wave velocity and S-wave velocity of reservoir rock and can calculate the elastic parameters reflecting the comprehensive properties of skeleton and pore fluid.…”

Research on Transformation of Connate Water to Movable Water in Water-Bearing Tight Gas Reservoirs

“…In experimental research on formation water mobility, scholars often employ methods such as X-ray diffraction, scanning electron microscopy, and centrifugation combined with nuclear magnetic resonance [27][28][29]. For instance, Liu et al [17] and Wang et al [30] conducted nuclear magnetic resonance experiments to investigate the impact of microscopic pore structure on formation water mobility in tight reservoirs. They concluded that variations in throat types and the distribution of pore throat radii are the primary factors influencing the saturation of movable fluids.…”