Experimental Investigation of Pore Structure and Movable Fluid Traits in Tight Sandstone

Abstract

Whether the variation of pore structures and movable fluid characteristics enhance, deteriorate, or have no influence on reservoir quality has long been disputed, despite their considerable implications for hydrocarbon development in tight sandstone reservoirs. To elucidate these relationships, this study systematically analyzes pore structures qualitatively and quantitatively by various kinds of direct observations, indirect methods, and imaging simulations. We found that the uncertainty of porosity measurements, caused by the complex pore-throat structure, needs to be eliminated to accurately characterize reservoir quality. Bulk water was more easily removed, while surface water tended to be retained in the pores, and the heterogeneity of pore structures was caused by the abundance of tiny pores. The rates of water saturation reduction in macropores are faster than those for tiny pores, and sandstones with poor reservoir quality show no marked descending of lower limits of movable pore radius, indicating that the movable fluid would advance exempted from the larger pores. This study suggests that the deterioration of reservoir quality is strongly affected by the reduction of larger pores and the aqueous phases tended to remain in the tiny pores in the forms of surface water.

An improved method to characterize the pore-throat structures in tight sandstone reservoirs: Combined high-pressure and rate-controlled mercury injection techniques

“…Currently, there are various methods to characterize the pore-throat structure of tight sandstones, including polarizing light microscopy (PLM), field emission scanning electron microscopy (FE-SEM), electron backscatter diffraction microscopy (EBSD-SEM), focusing ion beam microscopy (FIB-SEM), micro/nanoscale X-ray computed tomography (X-CT) nuclear magnetic resonance (NMR), nitrogen adsorption, high-pressure mercury injection (HPMI), and rate-controlled mercury injection (RCMI) (Bera et al., 2011; Geet et al., 2001; Liu et al., 2019; Xu et al., 2019; Zhou et al., 2019). Although each method has its own advantages in characterizing the structure of pore-throats, there are also respective limitations: PLM and various SEM methods are applied directly to examine the pore-throat size, geometry, and type but fail to obtain quantitative parameters (Loucks et al., 2009).…”

Characterization of Shale Pore Structure by Multitechnique Combination and Multifractal Analysis and Its Significance

“…NMR. The NMR T 2 curves were expressed by the pore size distributions where each signal amplitude was represented by its volume [53,54]. In this research, the T 2 spectrum before and after centrifugation was investigated, and the curves were presented in Figure 5.…”

Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

“…Their microscopic geological characteristics, pore throat genetic mechanisms, distribution heterogeneity characteristics, and fluid seepage mechanisms are different from those of conventional and general low permeability reservoirs [2,3]. In view of the characteristics of tight reservoirs, such as strong heterogeneity, fine pore throats, and difficult fluid flow, previous researchers have conducted much effective work, mainly focusing on the pore structure characterization of tight reservoirs, movable fluid saturation evaluation, and influencing factors of reservoir effectiveness [4,5]. Presently, the heterogeneity of conventional reservoirs is characterized by "a large number of" test data using parameters such as the coefficient of variation, sorting coefficient, and mean coefficient [6].…”