Swelling Rock Impacted By High Pressure Water Jet And Its Application In Coal Mine

In conventional wet drilling process, mudstone in hole will quickly expand when encountering water, which causes the space between drill pipe and borehole to close or partially close and leads to the drill tool clip or stuck, affecting drilling and later extraction activity schedule. Serious pipe-holding accidents will cause the loss of the drill tools and cause damage to property also.Based on Pingdingshan Coal Group Co.,Ltd. key project, aiming at the pipe-holding problem in drilling cross swelling mudstone, the high pressure water jet impact swelling mudstone experiment research has been carried out, which has verified the validity of high pressure water jet cutting swelling mudstone drilling to solve the problem of pipe-holding. At first, the high pressure water jet impact mudstone experiment has been carried on. The influence of key parameters to impact effect of swelling mudstone has been analyzed. The paper has obtained the suitable range of parameters in the field application. Secondly, through on-site validation the research finds that high pressure water jet cutting swelling mudstone drilling can efficiently solve pipe-holding problem. So high pressure water jet cutting swelling mudstone provides a new way to prevent pipe-holding problem when pipe crosses the swelling mudstone and it is of great significance for drilling and accidents to prevent gas disasters in coal mine. The main conclusions are stated as follows:① The paper applied high pressure water jet to impact swelling mudstone, studied the impact results for mudstone gotten from a coal mine. Research results show that impact depth, rate and diameter increases with the increase of impact parameters, overall impact rate presents a trend in time, the impact rate decreases at the first stage, then increases at the second stage, decreases at last. Because the presence of surface or radial constraint increases at first, then decreases and increases at last during the impact process corresponding stage to affect the impact rate change. Secondly, the distance is an important factor to affect impact rate. In the whole impact process by high pressure water jet, the stability of rock specimen is well and has no visible cracks in rock surface by naked eye. Within 1~5minutes, the rock fragment is small, whose width and thickness are less than 20 mm. Within 5~10minutes, rock fragment is produced more than 20 mm width.② Based on experiment results, the appropriate parameter of field test is obtained, including 2mm nozzle diameter, 5minutes impacting time, 30~35MPaimpact pressure. The field test results verify that the parameters conform to the requirements of test field.③ Based on the experimental data and analysis results, the field test is carried out. Compared with traditional drilling, the research has come to the conclusion that the drilling applied by high pressure water jet to cut swelling mudstone can reduce pipe-holding rate and solve the pipe-holding problem.