Effects of Nanopore Structure Heterogeneity of Coal Samples on Adsorption Ability and Porosity–Permeability Variation

Abstract

The occurrence and migration process of coalbed methane are affected by the nanopore-fracture structure. Meanwhile, coal reservoir adsorption ability and porosity−permeability variation are two core factors to characterize the occurrence and migration characteristics. Research on the effect of nanopore structure heterogeneity on the surface free energy and variation of porosity and permeability is important. In this paper, the physical properties and pore size distribution of five groups of coal samples were analyzed using nuclear magnetic resonance (NMR) tests. Then, hightemperature and high-pressure isothermal adsorption (HTHP) and overburden porosity−permeability tests (OPPT) were used to characterize surface free energy and porosity and permeability variation rate parameters of coal reservoirs. Main conclusions are as follows. All the samples can be divided into adsorption pore-developed and larger pore-developed types. ( 1) Multifractal results show that total pore volume distribution heterogeneity (D −10 −D 10 ) is determined by a lower value area of pore volume (D −10 −D 0 ). D −10 −D 0 represents seepage pore distribution heterogeneity; as it increases, irreducible water saturation decreases. Also, D 0 −D 10 represents adsorption pore distribution heterogeneity and T 2,cut-off decreases with the increase in D 0 −D 10 . ( 2) With the increase in adsorption pressure, the reduction rate of surface free energy increases rapidly during lower pressure (adsorption pressure is smaller than 6 MPa), and then its change is smaller than that of higher pressure. At the same adsorption pressure, the reduction rate of surface free energy decreases with the increase in adsorption pore volume. The Langmuir volume and adsorption capacity gradually increase with the increase in D −10 −D 0 .(3) Compressibility by using permeability variation is between 0.06 and 0.08 MPa −1 . The porosity and permeability variation rate has a positive correlation with seepage pore volume and D −10 −D 0 , and then this value decreases with the increase in adsorption pore volume. (4) Mechanical parameters (Young's modulus and Poisson's ratio) have an obvious linear relationship with pore volume, and they are not affected by heterogeneity parameters (D 0 −D 10 and D −10 −D 0 ) of pore size distribution.

Hierarchical self‐assembly of tannic acid/diethylenetriamine on polypropylene for high‐performance separator

“…29 As a suitable substitute, organic coatings were applied on the surface of polyolefin microporous films. Organic coatings such as polydopamine (PDA), 30 polyvinylidene fluoride (PVDF), 31 cellulose diacetate (CDA), 32 polyvinyl alcohol (PVA), 33 aramid nanofiber (ANF), 34 poly(methyl methacrylate) (PMMA), 35 polyimide (PI), 36 and poly(pphenylene terephthalamide) (PPTA) 37 are applied to polyolefin separators. The reason for organic coatings to be applied to the surface of polyolefins is because there are a large number of polar groups in the organic coatings, which have affinity for the electrolyte, thereby enhancing the absorption and retention capacity of polyolefin separator for the electrolyte and improving battery performance.…”

Evolution Characteristics of the Microstructure with Different Fracturing Fluids: An Experimental Study of Guizhou Bituminous Coal

“…Affected by the shortage of fossil energy and the greenhouse effect, all countries in the world are actively exploring new energy. , Coalbed methane is a new type of clean energy with broad application prospects, which has attracted the attention of governments all over the world. , According to the data of the International Energy Agency (IEA), the total global coalbed methane resources buried at a depth of less than 2000 m can reach 260 trillion m 3 , which is more than twice the proven reserves of conventional natural gas . However, the coal seams are less permeable and need to be hydraulically fractured to increase the permeability before the drainage of coalbed methane, especially in China. , Fracturing fluid is a key factor affecting the hydraulic fracture morphology and coal microstructure and plays an important role in the process of hydraulic fracturing. − …”

“… 3 , 4 According to the data of the International Energy Agency (IEA), the total global coalbed methane resources buried at a depth of less than 2000 m can reach 260 trillion m 3 , which is more than twice the proven reserves of conventional natural gas. 5 However, the coal seams are less permeable and need to be hydraulically fractured to increase the permeability before the drainage of coalbed methane, especially in China. 6 , 7 Fracturing fluid is a key factor affecting the hydraulic fracture morphology and coal microstructure and plays an important role in the process of hydraulic fracturing.…”