Experimental investigation on the effect of ethanol on micropore structure and fluid distribution of coalbed methane reservoir

Abstract

<jats:p> The development of coalbed methane not only ensures the supply of natural gas but also reduces the risks of coal mine accidents. The micropore structure of coalbed methane reservoir affects the seepage of coalbed methane; improvement of pore structure is one of the effective methods to enhance the efficiency of coalbed methane exploitation. In this study, low-pressure nitrogen gas adsorption, specific surface area analysis, nuclear magnetic resonance spectroscopy, and centrifugation experiment were used to evaluate the effect of ethanol on coal microscopic pore structure and fluid distribution during hydraulic fracturing. Seven coal samples were collected from the No. 3 coal seam in Zhaozhuang Mine, Qinshui Basin. The samples are mainly composed of micropores, transition pores, and mesopores. The experimental results show that ethanol can significantly change the pore structure by increasing the pore diameter. The average specific surface area, pore volume, and pore diameter of rock samples before ethanol immersion are 1.1270 m<jats:sup>2</jats:sup>/g, 0.0104 cm<jats:sup>3</jats:sup>/g, and 14.20 nm, respectively. The three parameters of rock samples after ethanol immersion are 0.5865 m<jats:sup>2</jats:sup>/g, 0.0025 cm<jats:sup>3</jats:sup>/g, and 29.37 nm. Ethanol improves the connectivity between micropores and mesopores. The average irreducible fluid saturation of samples saturated with formation water after centrifugation is 86%, and the average irreducible fluid saturation of samples soaked in three concentrations of ethanol solution decreases. It is considered that an ethanol solution of 0.4% concentration has the best effect on improving the pore structure and fluid distribution. </jats:p>

Effect of Nanoparticle Adsorption on the Pore Structure of a Coalbed Methane Reservoir: A Laboratory Experimental Study

“…The loose property of cores limits the higher centrifugal speed; it is known from the previous experiments in the same block that destructive cracks appeared in the sample above a speed of 2000 rpm. 22,23 Therefore, the maximum centrifugal speed designed in this experiment was 2000 rpm. The centrifugal process lasted 40 min under each speed, and then the core was weighed.…”

Experimental Investigation on Pore-Fracture Variations in Coal Affected by Carbon Disulfide

“…This may be due to the low degree of pore development in anthracite, which renders carbon disulfide ineffective in increasing the pore connectivity of the coal sample. Zhou et al 30 established a standard equation of porosity versus fluid volume to calculate the porosity of coal as follows:…”

“…Zhou et al established a standard equation of porosity versus fluid volume to calculate the porosity of coal as follows: ϕ = V ′ V × 100 % = 6 S + a b V × 100 % where ϕ is coal porosity; V ′ is the volume of solution in coal (cm 3 ; V is the coal sample’s volume (cm 3 ); S is the integration region of the NMR spectrum; and a and b are constants. S is calculated as follows: S = ∫ A ( T i ) normald T where T i is the time in the NMR spectrum; A is the amplitude corresponding to T i .…”