Dynamic monitor on coal reservoir water system during drainage process of coalbed methane well

In order to study dynamic propagation characteristics of coal reservoir water system during drainage process of coalbed methane well, based on different electrical conductivity of different lithology and water content of coal strata, a CBM production well in Qinnan area was chosen to conduct transient electromagnetic dynamic detections of coal reservoir water system before drainage and after half a year respectively. A rectangular survey grid of 400 m×300 m was set up with 16 survey lines perpendicular to the strata strike and 400 survey points distributed in each line, resulting in an observation coordinate network of 20 m×10 m within the survey grid. By means of data acquisition, data processing and quantitative interpretation, apparent resistivity bedding slice chart, comparison diagram of coal apparent resistivity and apparent resistivity section of each survey line and point were available before drainage and after half a year. The analysis results show that, distribution of coal reservoir water system is relatively uniform before drainage, while its anisotropy becomes very obvious after half a year. In the poor connectivity regions, apparent resistivity of coal seam and roof sandstone increases in different degrees because static water reserves of coal reservoir water system are partly dewatered, to the contrary, that of coal seam and roof sandstone in the preferable connectivity regions decreases in a certain range because of hydraulic dynamic supply.