Development of Downhole Explosion Monitoring System for Gas Drilling

Abstract Continental strata in Northeast Sichuan presents poor drillability due to high formation pressure, which leads to low ROP, wellbore inclination and lost-circulation with mud drilling technique. Gas drilling not only dramatically improves ROP and well quality, but also decreases construction cycle. However, this method was apt to trigger downhole explosion through payzones drilling, which would result in downhole tool broken, drilling failure and even well abandonment. During the exploitation of gas reservoirs in Northeast Sichuan, downhole explosion has happened in P104-1, P303-1, Y2 and Y3 wells, and these severe accidents provide an important incentive for developing a downhole explosion monitoring system for gas drilling to decrease downhole explosion risk. This paper will focus on the development of this system based on MIC-2718-a high-gain, high-performance multifunction DAS card-and other high-precision chemical sensors, which can monitor the concentration changes of CO2, CO, O2, H2S and CH4 in real-time. Visual C++ was employed to develop the real-time data acquisition and display interface, which are useful to display and save or playback curves of real-time data, what's more, intelligent alarm function is also available. This system features simple installation, convenient wire routing and great system stability. Furthermore, the usage of new developed downhole explosion monitoring system provides a safe downhole environment for gas drilling.