Coupling Effect of Temperature, Gas, and Viscoelastic Surfactant Fracturing Fluid on the Microstructure and its Fractal Characteristics of Deep Coal

Self Cite

Water plays an important role in carbon dioxide (CO2) enhanced coalbed methane exploitation and CO2 geological sequestration at deep geological conditions. We performed mercury intrusion porosimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction analysis on coal samples with different moisture contents after supercritical carbon dioxide (ScCO2) treatment to study the effect of different moisture contents on deep coal seam treatment by ScCO2. Using these experimental techniques, the effects of ScCO2 treatment on the microstructure of coal samples with different moisture contents were obtained. The results showed that the combination of ScCO2 and water in coal samples can cause mineral dissolution, increase the damage degree of coal structural defects, reduce the number of aromatic structures and oxygen-containing functional groups, and then lead to the expansion of the pore and fracture volume, especially the micropore volume. Moreover, with increasing the moisture content, the micropore volume of the coal samples under ScCO2 interaction with the presence of water exhibited an increasing trend. The number of oxygen-containing functional groups in the coal samples decreased. The peak position difference (G – D1) decreased first and then plateaued, and when the moisture content was in the range of 5.85–7.19%, the damage degree reached the maximum. The effect of water and ScCO2 on the dissolution of clay minerals in the coal samples was greater than that on the carbonate minerals.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Effect of Supercritical Carbon Dioxide (ScCO₂) on the Microstructure of Bituminous Coal with Different Moisture Contents in the Process of ScCO₂ Enhanced Coalbed Methane and CO₂ Geological Sequestration

Wang

et al. 2022

Self Cite

“…To ensure the uniformity of the test, all coal samples were taken from the same piece of coal. The samples were then crushed, and coal samples with a particle size of approximately 1 mm were screened out. , To study the change pattern of the chemical structure of coal under the coupling effect of temperature, gas, and VES fracturing fluid, especially for high temperature and high gas pressure conditions, geological data of Chinese coal seams were evaluated. The test parameters for group C were developed, and groups A and B were designed as control groups, as shown in Table .…”

Section: Methodsmentioning

confidence: 99%

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

Wang

et al. 2022

Self Cite

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.

“…The hydraulic fracturing technology reduces oil flow resistance and improves oil recovery in tight reservoirs . Therefore, it is very important to develop a suitable fracturing fluid with high efficiency, low cost, strong sand-carrying capacity, temperature resistance, and shear resistance in the process of fracturing construction. − Compared with the traditional natural guar gel fracturing fluid and the synthetic polymer fracturing fluid, a clean fracturing fluid has obvious advantages of simple compositions, residue free after gel breaking, high flowback rate, and low formation damage. − The main driving mechanism for the formation of the clean fracturing fluid is the interaction between viscoelastic surfactants and counterion salts to form a complex three-dimensional network structure overlapped by wormlike micelles. − Under tensile or shear forces, the wormlike micelle network has characteristic rheological properties that allow the clean fracturing fluid to quickly return to its original state after being pumped at high speed.…”

Section: Introductionmentioning

confidence: 99%

Development and Performance Evaluation of a Novel Silica Nanoparticle-Reinforced CO₂-Sensitive Fracturing Fluid with High Temperature and Shear Resistance Ability

Liu

Zhao

et al. 2022

In order to further increase the temperature and shear resistance of a conventional CO2-sensitive clean fracturing fluid, a novel silica nanoparticle-reinforced CO2-sensitive fracturing fluid system was developed. The system was prepared with the compositions of 2.0 wt % N-[3-(dimethylamino) propyl] oleamide, 1.5 wt % sodium p-toluene sulfonate (NaPts), and 0.025 wt % silica nanoparticles. The rheological properties, temperature resistance, shear resistance, sand-carrying capacity, gel-breaking property, and core damage property of the system were systematically studied and evaluated. Compared with the conventional CO2-sensitive fracturing fluid system, the silica nanoparticle-reinforced CO2-sensitive fracturing fluid system has a better viscosity increase effect, and the zero-shear viscosity increases from 2900 to 3500 mPa·s. By adding and removing CO2, the viscosity of the system can be repeatedly converted from high to low, and the reusable property can be realized. After introducing silica nanoparticles, the temperature resistance ability of the clean fracturing fluid increases from 100 to 130 °C, the sand-carrying effect increases by 23%, rapid and thorough gel breaking occurs, and core damage is less than 13%. We expect that this study can broaden the application of the CO2-sensitive clean fracturing fluid in low permeability, high-temperature reservoirs and provide a theoretical basis for field applications.