Rock Pore Structure Damage Due to Freeze During Liquid Nitrogen Fracturing

Cai, Chengzheng; Li, Gensheng; Huang, Zhongwei; Shen, Zhonghou; Tian, Shouceng

doi:10.1007/s13369-014-1472-1

Cited by 62 publications

(23 citation statements)

References 15 publications

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“…Cai et al 31,32 also used NMR to study rock and coal that had been frozen using LN 2 . They discovered that LN 2 causes greater freezing damage to coal compared to other rocks.…”

Section: Previous Studiesmentioning

confidence: 99%

Pore Structure in Coal: Pore Evolution after Cryogenic Freezing with Cyclic Liquid Nitrogen Injection and Its Implication on Coalbed Methane Extraction

et al. 2016

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Freezing and thawing cycles occur with cyclic liquid nitrogen (LN 2 ) injection in coal. The freeze−thaw treatment damages the pore structure of coal and thus increases its permeability. In this study, NMR and strain monitoring were employed to investigate the changes in coal structure when the coal specimens were under cryogenic treatment using LN 2 . We classified freeze−thaw process into four stages; stages I and III are dominated by seepage pore development, and stages II and IV are dominated by adsorption pore development. It was found that LN 2 freeze−thaw cycles can cause structural deterioration in the coal so as to improve both fracture density and overall permeability. The results demonstrate that the rate of increase of both the effective porosity and total porosity of the coal are positively correlated with the LN 2 freezing time and the number of freezing cycles but negatively correlated with the residual porosity. For the same absolute LN 2 freezing time, cyclic freeze−thawing has a greater effect on the rate of growth of pore spaces and reduction of P-wave velocity in the coal compared with single freeze−thaw treatment. It was also found that the number of freeze−thaw cycles is a very important factor for the creation of larger pores, pores that can connect the fracture network. The results suggest that appropriate control of the number of freeze−thaw cycles can result in effective fracturing of coal.

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“…Cai et al 31,32 also used NMR to study rock and coal that had been frozen using LN 2 . They discovered that LN 2 causes greater freezing damage to coal compared to other rocks.…”

Section: Previous Studiesmentioning

confidence: 99%

Pore Structure in Coal: Pore Evolution after Cryogenic Freezing with Cyclic Liquid Nitrogen Injection and Its Implication on Coalbed Methane Extraction

et al. 2016

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“…They also observed that when subjected to liquid nitrogen, the mechanical strength of the coal decreased, and the damage was positively correlated to water saturation. (Cai et al 2014a) Cai et al (2015) submerged some dry coal samples in LN2. While they observed surface cracks along the macro-fractures, the experiments revealed an increase of up to 34% and 93% in the compressive strength and permeability of treated samples, respectively (Cai et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Coal fracturing through liquid nitrogen treatment: a micro-computed tomography study

et al. 2020

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Low permeability of coal has been a constant obstacle to economic production from coalbed methane reservoirs, and liquid nitrogen (LN2) treatment has been investigated as one approach to address this issue. This study examined LN2 fracturing of a bituminous coal at pore-scale through 3D X-ray micro-computed tomography. For this purpose, a cylindrical sample was immersed into LN2 for 60 min. The micro-CT results clearly showed that the rapid freezing of the coal with LN2 generated fracture planes with large apertures originating from the pre-existing cleats in the rock. This treatment also connected original cleats with originally isolated pores and micro-cleats, thereby increasing pore network connectivity. Moreover, scanning electron microscopy highlighted the appearance of continuous wide conductive fractures with a maximum opening size of 9 µm. Furthermore, a nano-indentation technique was used to test the effect of LN2 on coal mechanical properties. The indentation moduli decreased by up to 14%, which was attributed to the increase in the cracked rock compressibility, showing considerable fracturing efficiency of the LN2 treatment. Through in-situ microscopic visualisation and surface investigation, this study quantified the pore structure and connectivity evolution of the rock based on the morphological alteration, and demonstrated the promising effect of LN2 freezing on fracturing of bituminous coals, thus aiding coalbed methane production. The significance of this study was investigating the mechanisms associated with and the efficiency of LN2 treatment of a coal rock in a 3D analysis inside the rock.

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“…The feasibility of cryogenic fracturing in reservoir stimulation was proved by a well-known field test using LN 2 as the fracturing fluid in 1998 [5]. Thereafter, various studies were carried out to investigate the cryogenic fracturing [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Displacement of Water by Sub-Zero N-Hexanol in a Straight Channel

Huang

Wang

2020

Energies

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Series of displacement tests of water by cold n-hexanol (below 0 °C) in a straight tube were conducted to investigate the freezing-accompanied displacement process, which occurs during the cryogenic fracturing process. The interrelationship between water freezing and displacement flow was studied. It was found that the displacement flow could significantly affect the water distribution in the flow channel. Along with the displacement proceeding, the n-hexanol overtook the water in the flow direction gradually, and the water in the center of the channel was driven to the edge area. Moreover, the initially integrated water phase split into several parts during the displacement process. Once the water freezing occurred, two typical ice blockage patterns, i.e., complete ice blockage and incomplete ice blockage, were observed. In incomplete ice blockage pattern, the channel cross-section was partly occupied by the ice phase, which mainly affected the rate of subsequent fluid flow. In complete ice blockage pattern, the channel cross-section was fully occupied by the ice phase, which cut off the fluid flow in the original direction. Based on the test results, the influences of the initial water temperature, initial water column length and flow rate of n-hexanol on the formation of different ice blockage patterns are discussed. The decrease of the initial water temperature and the increase of the initial water column length are preferred to induce the occurrence of complete ice blockage. However, changing n-hexanol flow rate could lead to the occurrence of both incomplete ice blockage and complete ice blockage, which depends on the actual situations.

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Rock Pore Structure Damage Due to Freeze During Liquid Nitrogen Fracturing

Cited by 62 publications

References 15 publications

Pore Structure in Coal: Pore Evolution after Cryogenic Freezing with Cyclic Liquid Nitrogen Injection and Its Implication on Coalbed Methane Extraction

Pore Structure in Coal: Pore Evolution after Cryogenic Freezing with Cyclic Liquid Nitrogen Injection and Its Implication on Coalbed Methane Extraction

Coal fracturing through liquid nitrogen treatment: a micro-computed tomography study

Experimental Study on Displacement of Water by Sub-Zero N-Hexanol in a Straight Channel

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