Characteristics of the Coal Fines Produced from Low-Rank Coal Reservoirs and Their Wettability and Settleability in the Binchang Area, South Ordos Basin, China

Abstract

By using proximate analysis, X-ray diffraction mineral analysis, scanning electron microscope, contact angle measurement, and settlement simulation experiment, the coal fines produced from the coalbed methane wells of Binchang area were used to study the characteristics including particle size distribution, composition, morphology, wettability, and settleability. The results show that the particle size of coal fines produced from coalbed methane wells are mainly >20 mesh, ranging of 1-400 μm, and the particle size distribution curve is mainly dominated by the main-secondary bimodal type, with the main peak of 30-300 μm. The particle size from large to small is drill cutting coal fines, flowback coal fines, bailing coal fines, and pipeline filter coal fines. In terms of ash content, coal fines are higher than coal seam, and drilling cuttings are higher than bailing coal fines, while the fixed carbon content of the former is lower than that of the latter. The minerals of coal fines are mainly kaolinite, illite, quartz, and other 6 minerals, and the mineral types of drilling coal fines are the most abundant, while the bailing coal fines only contain illite and quartz. The roundness of coal fine particles ranges from excellent to poor in the order of bailing coal fines, pipeline filter coal fines, flowback coal fines, and drilling cuttings. However, the sorting of drilling cuttings is excellent, and the particle edges are straight, neat, and smooth, while the sorting of bailing coal fines is poor, and the particle edges are curved, uneven, and rough. The contact angles of coal fines are 40.25°-69.5°, indicating hydrophilous. The wettability of bailing coal fines is better than that of drilling cuttings. The particle size has a negative correlation with the wettability effect. The more obvious the modification effect of positive wetting agent is, the worse the modification effect of negative wetting agent is. The modification of surfactant has nothing to do with the particle size of the coal fines, but is closely related to organic components and minerals. The larger the coal particle size, the higher the settling rate, and the higher the ash content and the lower the fixed carbon content, the faster the settling rate. With the dividing point 150 mesh, the settling rate of large particles is mainly affected by particle size, while that of small particles is affected by the composition.

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…According to the previous studies, the cleat aperture can vary from 5 to 400 μm, − while the coal fines sizes are in the range of 10–1000, 1–400, 0.1–200, or 1–14 μm . It is, therefore, very likely that the coal fines are retained in the cleats, leading to permeability reduction or even complete closure of cleats.…”

“…Coal fines are a common issue in almost all major CSG fields globally, such as in Bowen Basin (Australia), San Juan Basin (USA), Qinshui Basin (China), and Junggar Basin (China) . Coal fines are small particles released from the coal and mainly consist of nonorganic minerals like clay, kaolinite, quartz, and others. ,, They can be divided into two types: (i) primary coal fines, which refer to the coal fines that already exist before the production, and (ii) secondary coal fines, which are production induced. , More coal fines are observed during the dewatering and two-phase flow stages than in other stages, , as illustrated in Figure .…”

“…203,205,206 They can be divided into two types: (i) primary coal fines, which refer to the coal fines that already exist before the production, and (ii) secondary coal fines, which are production induced. 206,207 More coal fines are observed during the dewatering and two-phase flow stages than in other stages, 208,209 as illustrated in Figure 13.…”

“…Chen et al 206 Laboratory characterization of coal fine particle size, composition, morphology, and wettability.…”

An Experimental Study on the Particle Size and Shape Distribution of Coal Drill Cuttings by Dynamic Image Analysis

“…The accurate measurement of particle size distribution (PSD) of coal samples is significant to both scientific research and engineering, such as coal combustion [1][2][3][4][5], coal chemical industry [6][7][8][9], adsorption and desorption [10][11][12], and coal and gas outburst [13,14]. There are more than one hundred methods and instruments to measure particle size distribution, including sieving, settling velocity measurements, laser diffraction (LD), photon correlation spectroscopy, sound spectrum method, dynamic light scattering method, scanning electron microscope, and X-ray diffraction [15][16][17][18][19][20]. Of these methods, sieving and LD particle analyzers are widely used for measuring general coal particles (>10 μm) because of their high accuracy, simple operation, fast speed, and high repeatability.…”