Layered layout of high-level directional boreholes and analysis of gas drainage effect

Abstract:

In order to improve the effect of high-level directional drilling in the roof on the goaf and upper corner gas control， a layered arrangement of high-level directional boreholes was proposed， and field tests were carried out in Shuguang Coal Mine. Analysis of gas drainage data of high-level directional boreholes at different depth， and gas drainage effect of high-position directional boreholes in the entire gas drainage cycle showed that gas drainage effect of high-position directional boreholes fluctuated throughout the entire drainage cycle in general. Drainage effect was relatively stable over the middle hole section since it was located in the roof crack zone； while gas drainage effect fluctuated greatly over both top and bottom hole sections since they were located in the build-up sections of the drill holes and did not enter the roof fissure zone， and were affected by the overlap of the drainage holes from the front and rear drill sites. In order to improve gas drainage effect of high-position directional drilling， a large entry angle or a high-bent mud motor can be used to reduce the length of the build-up hole section and increase the overlap length of the drainage holes from the two adjacent drilling sites so as to reduce the proportion of both top and bottom hole sections， and increase that of the middle hole section.

Key words:high-level directional drilling;mined-out area;gas drainage;layered layout;drainage cycle