Pore Structure Characterization of the Tight Reservoir: Systematic Integration of Mercury Injection and Nuclear Magnetic Resonance

Abstract

Pore structure is the most important factor affecting reservoir quality and petrophysical property of tight reservoir. The effective characterization of pore structures, including pore radius distribution (PRD), throat radius distribution (TRD), pore-throat radius distribution (PTRD), relevant pore structure parameters, etc., is of great importance for the oil exploration and exploitation. Taking the tight sandy conglomerate reservoir as research target of tight reservoir, this paper characterizes the pore structures by a combination of experiments on parallel core samples. These experiments include highpressure mercury injection (HPMI), constant-rate mercury injection (CRMI), nuclear magnetic resonance (NMR), as well as microscopic analysis of casting thin sections and scanning electron microscopy (SEM). This paper systematically analyzes the advantages and shortcomings of these commonly used experimental techniques. And then, novel methods are proposed to characterize the pore structure (especially the full-range PRD, TRD, and PTRD) by utilizing the advantages of these techniques. In addition, an advanced pore classification scheme is proposed to reclassify the pore types. Finally, the controls of the pore structure on the flow characteristics are investigated, which in turn further demonstrates the correctness and importance of the proposed novel methods for characterizing pore structures. In summary, this study proposes novel methods to characterize the pore structure by integration of HPMI, CRMI, and NMR and provides insights into the pore structure characteristics of the tight sandy conglomerate reservoir.

Controlling Effects of Tight Reservoir Micropore Structures on Seepage Ability: A Case Study of the Upper Paleozoic of the Eastern Ordos Basin, China

“…In previous studies, the influencing factors for reservoir seepage characteristics were analyzed using HPMI, CRMI, and NMR experimental data (Ming et al, 2015;Gao et al, 2016;Xi et al, 2016;Wang et al, 2018). The distribution pattern of throat radius, effective porosity, and throat number affected the seepage ability of a reservoir.…”

“…In previous studies, the throat size and distribution characteristics were considered the main controlling factors that affected the movable fluid saturation of a reservoir (Ming, 2015;Gao et al, 2016;Wang et al, 2018). However, the analysis of the relationship between micropore structure parameters and movable fluid saturation shows that the movable fluid saturation has good positive correlation with total pore mercury saturation, total mercury saturation, effective pore volume per unit volume, and sorting coefficient.…”

Evaluation of Displacement Effects of Different Injection Media in Tight Oil Sandstone by Online Nuclear Magnetic Resonance

“…As shown in Equation (1), the relaxation time distribution reflects the specific surface area of the rock, which corresponding to the pore size [13,49,50]. The surface relaxation strength ρ 2 is a parameter for characterizing fluid properties in porous media, which is related to the internal surface properties and mineral composition.…”

“…The core NMR T 2 spectrum can be converted into the core pore distribution [13,54]. For tight oil sandstone, the pores were divided into nanopores, micro-nanopores, sub-micropores, and micropores according to pore radius [44,55], which were 0.05, 0.1, and 1 µm.…”

“…The difficulty to develop tight oil reservoirs is mainly in two aspects. First, the tight oil reservoir has small pore throat radius [13], high clay mineral content, low permeability and obvious non-Darcy seepage [14,15], which makes it difficult to supplement formation energy by conventional water injection [16]. Second, the production of water flooding development decreases rapidly and the recovery ratio is low, thus it is necessary to inject medium into formation to supplement formation energy for a long time [17].…”