Effects of acid-based fracturing fluids with variable hydrochloric acid contents on the microstructure of bituminous coal: An experimental study

Wang, Zepeng; Ge, Zhaolong; Li, Ruihui; Liu, Xianfeng; Wang, Haoming; Gong, Shengkai

doi:10.1016/j.energy.2021.122621

Cited by 30 publications

(41 citation statements)

References 35 publications

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“…b kx e = (5) with k = 0.114 27 and x as the distance from the nozzle outlet to the jet terminal, that is, the jet target distance, which is substituted into eq 4 u u…”

Section: Resultsmentioning

confidence: 99%

Fracture Characteristics and Failure Modes of Coal, Sandstone, and Shale Impacted by Water Jet under True Triaxial Conditions

Gao

Zhou

et al. 2022

Energy Fuels

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In recent years, the water jet technology has become an important means for processing unconventional oil and gas resources. With the exploitation of resources to the deep development, the study of the fracture characteristics and failure modes of true triaxial water jet rock breaking is of major importance for the application of the water jet technology in deeper crustal levels. We selected three typical unconventional gas reservoirs, coal, sandstone, and shale, as samples for our rockbreaking experiments of water jet under true triaxial conditions. On the basis of the rock failure criterion considering triaxial stress, we establish the rock-breaking energy criterion of water jet under true triaxial conditions and study the rock-breaking mode of water jet under true triaxial conditions. Experimental results document that the true triaxial water jet rock-breaking energy criterion can predict the rock-breaking threshold pressure well. With the increase of triaxial stress, the breaking threshold pressure of coal, sandstone, and shale increased by 92, 38, and 37%, respectively. Under true triaxial conditions, the failure characteristics and failure modes of different rocks impacted by water jet differ significantly. The water wedge action of coal is weakened, the volume of the crushing pit was reduced by 90%, and the failure is mainly caused by the shear failure that is induced by jet pressure. Sandstone is still dominated by the denudation failure that is caused by jet, but the degree of destruction is weakened, and the volume of the crushing pit was reduced by 38%. The shale has changed from tensile failure that is dominated by stress waves to erosion pit failure that is dominated by shear action. The results of the study provide a reference for the application of the water jet technology for the exploitation of unconventional oil and gas resources in deeper crust levels.

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“…b kx e = (5) with k = 0.114 27 and x as the distance from the nozzle outlet to the jet terminal, that is, the jet target distance, which is substituted into eq 4 u u…”

Section: Resultsmentioning

confidence: 99%

Fracture Characteristics and Failure Modes of Coal, Sandstone, and Shale Impacted by Water Jet under True Triaxial Conditions

Gao

Zhou

et al. 2022

Energy Fuels

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“… causes swelling of clay particles in the reservoir layer, resulting in a sharp decrease in the permeability of the lower well area;  water-oil emulsions are formed, which in some cases significantly reduce the permeability of the lower well area;  Capillary forces in the porous medium and its partial displacement from the porous channels can only be accompanied by a significant change in pressure, which makes it difficult for methane to move to the bottom of the well, especially with low conductivity reservoirs;  As a result of the interaction of the drilling mud filter with highly mineralized water, insoluble residues may form in the reservoir pores [4]. The penetration of polymers, starch, and calcium carbonate, which is part of the drilling mud into the productive layer of the drilled rock, changes the filtration properties of the formation during the formation of the filtration crust and leads to a decrease in the initial permeability [5].…”

Section: Introductionmentioning

confidence: 99%

Improving the efficiency of methane extraction from coal seams

Rabatuly¹,

Musin²,

Demin³

et al. 2022

KIMS/CUMR/MShKP

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This article presents possible reasons for the low productivity of wells for coal methane extraction and ways to resolve them using hydrochloric acid treatment of wells. A common reason for the low productivity of wells is a decrease in the permeability of the bottom-hole formation zone. Starch, calcium carbonate, and drilling rocks, which are part of the drilling mud, change the filtration properties of the layer during the formation of a filtration crust and lead to a decrease in the initial permeability. Hydrochloric acid treatment, during which clay rocks are dissolved, is an effective method of increasing the productivity of wells. It is used to increase pick-up and prevent contamination of the bottom-hole zone of the carbonate formation. The parameters affecting the effectiveness of hydrochloric acid treatments were considered. The results of the experience of the interaction of hydrochloric acid with a clay crust are presented and analyzed using approaches to the mechanics of multiphase media. Dependences of the rate of dissolution of clay rock on the concentration of acid solution are obtained. It is established that the treatment of the productive intermediate layer of the well with hydrochloric acid in a certain concentration, its use increases the technological and economic efficiency of wells. As a result of experimental work, it was found that hydrochloric acid with an HCL concentration above 18% has a negative effect on the internal equipment of the well when processing clay shells.

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“…Coal is an extremely complex and inhomogeneous organic rock that is heterogeneous, amorphous, and insoluble. − These complex structures of coal determine a series of macroscopic properties of coal, such as the gas adsorption properties and the mechanical properties. , It has been concluded that the interaction between gas and the coal molecular structure has an important influence on coal and gas protrusion. In addition, the type and number of coal functional groups and the skeleton structure will affect the adsorption properties of coal to gas, which will affect the gas extraction effect. , Due to the high temperature, high gas pressure, and other environments, the physical properties of deep coal such as the microstructure have changed greatly compared with the shallow coal, which lead to the further increase of the difficulty of the exploitation of coalbed methane (ECBM) and the risk of coal and gas outburst.…”

Section: Introductionmentioning

confidence: 99%

“…At present, the main methods used for coal chemical structure analysis are X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, etc. , Through these methods, we can analyze the surface functional groups, macromolecular structure, and mineral composition of coal. The macromolecular structure of coal, which contains a complex macromolecular network of organic structural units connected by covalent and noncovalent bonds of different sizes, is very complex .…”

Section: Introductionmentioning

confidence: 99%

“…After the coalification and tectonic effects are weakened, the microstructure of coal is shaped and remains basically stable. However, with the influence of some external factors in later mining activities such as coal washing, coal seam water injection, and hydraulic fracturing, the microstructure of coal may also change dramatically. ,− Hydraulic fracturing is a measure to crack the coal body by injecting a high pressure fracturing fluid into the coal seam so as to achieve the purpose of coal seam permeability enhancement. ,,, To achieve a better permeability enhancement effect, a fracturing fluid with strong modification on coal seam is applied to the hydraulic fracturing process, such as an acid-based fracturing fluid, viscoelastic surfactant fracturing fluid, etc. The addition of these chemicals will modify the coal and change its chemical structure, , for example, shedding of functional groups, condensation of aromatic rings, etc.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Chemical Structure of Deep Coal: An Experimental Study

Wang

et al. 2022

Energy Fuels

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The chemical structure of coal has an important influence on coalbed methane mining. Through Fourier transform infrared (FTIR) and Raman analysis of coal samples after coupling treatment of temperature, gas, and viscoelastic surfactant fracturing fluid (VES), we studied the evolution law of coal chemical structure. It was determined that the functional groups of coal decreased by approximately 30% with increasing temperature, showing an obvious temperature sensitivity. The VES fracturing fluids can destroy the functional groups of coal, and high temperature and high gas pressure conditions can seriously weaken the degree of destruction of the functional groups of coal by VES fracturing fluids but significantly enhance the destruction of the functional groups of coal by deionized water. Temperature, deionized water, and the use of VES fracturing fluid under a low temperature barely affect the macromolecular structure of coal, but when the temperature increases above 323.15 K, the coupling effect of temperature and VES fracturing fluid causes the position of the Raman peaks D1 and G for coal to move toward higher frequencies, the peak position difference to move toward lower frequencies, and the range of motion to be 10–18 cm–1. That is, the coupling effect of high temperature and VES fracturing fluid can make the macromolecular structure of coal become more ordered.

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Effects of acid-based fracturing fluids with variable hydrochloric acid contents on the microstructure of bituminous coal: An experimental study

Cited by 30 publications

References 35 publications

Fracture Characteristics and Failure Modes of Coal, Sandstone, and Shale Impacted by Water Jet under True Triaxial Conditions

Fracture Characteristics and Failure Modes of Coal, Sandstone, and Shale Impacted by Water Jet under True Triaxial Conditions

Improving the efficiency of methane extraction from coal seams

Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Chemical Structure of Deep Coal: An Experimental Study

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