Research On Influence Of Water On Coal Adsorptivity And Fluid Pressure Evolution Of Lignite In Turpan-hami Basin

In order to explore the water-bearing features of lignite reservoir and its influence on lignite adsorptivity, as well as its fluid pressure evolution, the lignite reservoir in eastern exploration area No.1, Dananhu Depression, Turpan-Hami Basin was chosen to analyze the water content and its bearing characteristics, and the influence of water on lignite adsorption was investigated with the methane adsorption experiments of equilibrium water coal samples which was compared with the experiments of air dried base samples. Moreover, the coal reservoir fluid pressure evolution process was revealed through the "four" history simulation in the study area with the basin numerical simulation software named Petro Mod. Research showed that, there were four water occurrence patterns including the external water, the pore water, the molecule water and the crystal water in the lignite of which the biggest influencing patterns on adsorption were the pore water and the molecule water, the normal influencing pattern was the external water, while the crystal water almost had no impact; The saturated adsorption quantity of dry air base coal samples decreased as temperature rose at low temperature(30-50℃), however, as temperature continued to go up, the saturated adsorption quantity of different kinds of coal samples presented the opposite variation tendency due to the shift of the positive effect of adsorption quantity increased caused by removal of different occurrence patterns of water and the negative effect of adsorption quantity reduced caused by increasing of the temperature; Lignite reservoir in the research area experienced a low temperature(Tmax=47℃) burial history under the stable tectonic evolution background in which thermogenic gas and biogenic gas both accounted for a certain proportion, but the amount of gas generated was small; The gas generation ratio determined the evolution of the gas generation pressurization, and since coal reservoir had low coalification degree(Ro, max=0.34%) and characteristics of self generation and self preservation, the contribution of hydrocarbon generation pressurization to the fluid pressure was weakened with a maximum value of less than 0.02 MPa, therefore the lignite reservoir pressure was mainly subject to the change of the hydraulic pressure which was under the control of the burial history; Although the gas bearing potential was poor(0.4 cm3/g), as buried depth increased, the preservation condition was good, which was in favour of coalbed methane(CBM for short) occurrence. The achievement of this research is of guiding significance for the exploration and development of CBM in lignite reservoir.