Study on Pore Structure of Shale Reservoir by Low Temperature Nitrogen Adsorption Method

Abstract

Shale gas is one of the most actively explored unconventional sources of natural gas. There are several types of pores in the shale reservoir, and their structural characteristics are complex. Evaluating the characteristics of the shale pore structure is the basis for understanding the shale reservoir performance and the oil and gas migration mechanism. In this paper, the micro- and nanopores of shale samples from the Yanchang Formation, Hunan basin, are studied by applying the low-temperature nitrogen adsorption method. Several pore structure parameters such as the specific surface area, the pore volume, and the pore size distribution of the analyzed samples are calculated. The predominant characteristics of nanopores that influence hydrocarbon accumulation and control the development of pores are discussed. The results indicate that the shale reservoir rocks from the study area are mainly mesoporous with an average pore size distribution between 2 and 50 nm. A small number of micropores (less than 2 nm) and macropores (more than 50 nm) are also present in the pore network. The development of micropores and mesopores in the shale samples is associated with organic matter content, while the development of macropores is linked to clay minerals content. Total organic carbon (TOC) content is the key element to control the nanopore volume and the specific surface area of the reservoir rocks from the study area. At the same time, the organic matter-enriched pore network also provides extensive space for the accumulation of shale gas.

Study on the Effect of Pore Structure on Desorption Hysteresis of Deep Coking Coal under High-Temperature and High-Pressure Conditions

“…The experiments were carried out using the ASAP2020 fully automatic specific surface area and porosity analyzer, as shown in Figure , using the principle of isothermal adsorption by the “static nitrogen adsorption capacity method”, with the help of the gas adsorption principle, the adsorption medium was nitrogen with 99.99% purity, and helium was used as the carrier gas. The test temperature was 77 K, and the test method was based on the pressure measurement method (GB/T19587-2004) . First, a certain mass (generally 3–4 g) of coal samples with diameters between 180 and 250 μm (60 and 80 mesh) was weighed for drying, and the samples were dried at 378 K for 2 h in the drying oven and then removed and cooled to room temperature.…”

“…The test temperature was 77 K, and the test method was based on the pressure measurement method (GB/T19587-2004). 27 First, a certain mass (generally 3–4 g) of coal samples with diameters between 180 and 250 μm (60 and 80 mesh) was weighed for drying, and the samples were dried at 378 K for 2 h in the drying oven and then removed and cooled to room temperature. Second, to ensure that the liquid nitrogen molecules could be effectively adsorbed on the surface of the experimental coal samples or fill the pores, the prepared coal samples were heated and degassed, and the evacuation temperature and time were 473.15 K and 5 h, respectively; third, the degassed experimental coal samples were exposed to low-temperature liquid nitrogen, and the experimental ranges of the relative pressures ( p / p 0 ) ranged from 0.0010 to 0.9950; P 0 is the saturated vapor pressure, and P is the equilibrium pressure of adsorption; finally, the low-temperature adsorption–desorption isotherms were constructed using the ASAP2020 analyzer, and the results of each pore structure parameter were automatically calculated according to the algorithms based on BET, Barrett–Joyner–Halenda (BJH) and D–R theories built into the computer software accompanying the analyzer.…”

Characteristics of Micro–Nano-Pores in Shallow Shale Gas Reservoirs and Their Controlling Factors on Gas Content

“…In physical experimental measurement techniques, depending on the pore size, methods primarily include low-temperature nitrogen adsorption, low-temperature carbon dioxide adsorption, high-pressure mercury 2 of 16 intrusion, and nuclear magnetic resonance (NMR) technologies [7]. Each technique targets pores within different size ranges; for example, low-temperature gas adsorption is suitable for detecting mesopores and micropores [8], while high-pressure mercury intrusion is more apt for characterizing macropores [9]. Although these methods have their strengths, limitations exist, such as the potential for high-pressure mercury intrusion to damage samples [10], whereas low-temperature gas adsorption can avoid sample destruction, thereby increasing sample usability [11].…”

Occurrence and Flow Behavior for Oil Transport in Mixed Wetting Nanoscale Shale Bedding Fractures

“…o w (6) where W Ao is the work of adhesion on the oil-wet surface, W Aw is the work of adhesion on the nonoil-wet surface, D o is the oilwet surface diffusion coefficient, and D w is the nonoil-wet surface diffusion coefficient. Homogeneous Mixed Wetting Nanoscale Shale Bedding Fracture (HMWF) Model Derivation.…”

“…Shale oil reservoirs are often characterized by the development of nanopores, complex mineral composition, and diverse fluid occurrence states. − The flow behavior and physical properties of fluids in nanoconfined spaces are completely different from those under bulk conditions. This is mainly reflected in the fact that (1) the interaction between the fluid and the solid wall becomes non-negligible, which causes changes in the physical properties of the fluid in nanoconfined spaces; − (2) the slip of the fluid on the surface of solid wall during the flow process in nanoconfined spaces becomes non-negligible; , (3) the flow in nanoconfined spaces is more easily affected by the wettability of the pore wall than in bulk conditions. , Considering these changes comprehensively, conventional theories cannot be directly applied to describe flow behavior in nanoconfined spaces.…”