Study On Explosion Risk Of Combustible Gas Mixtures In Air Drilling

The air drilling technology has been developed greatly all over the world in recent years. It is a practical technology and often the application of choice in dry, hard rock. The air drilling fluid medium is inexpensive and respectable rates of penetration can be achieved, compared to traditional drilling methods which use water or weighted drilling mud as drilling fluid medium. In terms of economic consideration with respect to drilling fluid expenditures, air drilling is a good choice. However air drilling is not without its impediments: it increases the potential for flammable or explosive gas mixtures to be present in the wellbore and surface piping during drilling. In this paper, studies related to explosion risk of combustible gas mixtures in air drilling were carried out.During the air drilling, the working procedures were various and complex that the equipments, workers and working condition were sufferring great explosion risk. In order to make certain these risk factors, the kinds of risk and potential risk were concluded and the main potential explosion risks existed in the process of air drilling were analyzed systematically, according to the practical applications of air drilling at home and abroad. The same time, the general steps of preliminary hazard analysis and fuzzy integrative evaluate method were introduced and adopted to fulfill the safety assessment of explosion risks in air drilling. Based on the risk identification of air drilling,the integrated drilling risk evaluation model was established and the safety assessment of explosion risks in air drilling were fulfilled objectively. A specially-designed apparatus was calibrated utilizing combustible mixtures, then the flammability characteristics of various mixtures were established. Additional tests were carried out utilizing nitrogen/combustible mixtures. Flammability limits were determined for each series of experiments, and the results used to design the safety features for air drilling, such as the minimum flow rate of circulating medium for drilling, the monitoring value of explosion and the limit value of oxygen content, were discussed. At last, several safety measures and guidelines for safe air drilling operations were made to minimize the potential for downhole and surface explosion, and reduce the property loss and casualty or hurt of workers.