Search

The well log inversion has been widely applied to forecast coal texture distribution due to its effectiveness and low investment. However, most research missed the low resolution of well logging data caused by the "boundary effect", which make it difficult to identify thin layers. Here a method to improve the vertical resolution of logging curves by Wavelet Transform was applied. The original logging curve was decomposed by two-level wavelet decomposition using sym 8 mother wavelet, and then the high-frequency wavelet coefficient (d 2) was weighted to reconstruct a new log curve to enhance the resolution of the thin-layer. Based on 160 reconstructed training logging datasets, the Linear Discrimination Analysis was used to establish a quantitative coal texture identification model by reducing the dimensionality of the data points and projecting them into a two-dimensional space. The validation results of coal texture are in good agreement with the coal core. Compared with the non-reconstructed curve, the recognition accuracy is greatly improved, especially for layers with a thickness < 20 cm. The combination of Wavelet Transform and Linear Discrimination Analysis provides a new way to predict coal texture using geophysical logging data. This method has been successfully applied to multiple (>20 layers) and thin (generally <2 m in thickness) seams in the western Guizhou province of China, with recognition accuracy >85%. [ABSTRACT FROM AUTHOR]

With 59 sets of well testing data from 32 wells, 70 coal seam gas data from 9 wells, and production data from 17 wells, the in situ stress distribution within depths of 136-1244 m and its implications for coal permeability (0.0001-1.56 mD), gas content (5-22 m3/t) and gas productivity in western Guizhou were investigated. Three major depth intervals with different stress regimes were identified. At depths of 800-1244 m, the horizontal stresses increased to high values with depth due to the compressional zone near the axis of the syncline. Permeability changes with depth were consistent with the effective stress variations. The 500–800 m depth interval with a normal faulting stress regime was favorable for good permeability (0.008-0.57 mD, mean 0.2 mD) and a stable pressure gradient (approximately 1 MPa/100 m), and the gas content generally increased with depth to a peak value at 800 m. For the 200-500 m and 800-1244 m depth intervals, extremely low permeability (0.0001-0.17 mD, mean 0.03 mD) resulted in discontinuous changes in gas content and pressure gradient (0.47-1.71 MPa/100 m). Overall, the stress release zone at depths of 500–800 m was favorable for coalbed methane extraction, which agreed with the measured production data. Low horizontal stress anisotropy in western Guizhou contributes to complex hydraulic fracture networks, individual seam fracturing with low proppant concentration and high fracturing fluid volume is suggested for multilayer commingled production. • In-situ stress distribution characteristics of coals in the Western Guizhou. • Permeability and resource distribution show similar belting as with stress regimes. • Stress release zone at 500–800 m depths are favorable for CBM extraction. • Low proppant concentration and high fluid volume are suggested for hydrofracturing. • Individual-seam fracturing is the most effective productivity enhancement method. [ABSTRACT FROM AUTHOR]