Safety Analysis And Evaluation For The Process Of Underbalanced Drilling

As oil resources gradually reduced in recent years, the exploration is increasingly becoming more and more difficult. Undoubtedly, people have to put emphasis on the large and small oil fields with complicated geological and surface conditions. As a result, underbalanced drilling technology has been becoming a leading technology in drilling industry, and this technology is conducive to develop such kind of failure reservoir. If there are inappropriate behavior and measures in the drilling, and this will result in a large mount of loss regardless of surface system or underground system, even lead to dangerous consequence to drilling personnel. Hence, improving the safety level of the process of underbalanced drilling is conducive to popularize and apply this technology, which is a trend of the increasing difficulty in exploration.This paper concludes possible dangerous factors in the process of underbalanced drilling by virtue of reading bibliography concerned materials over the world. Moreover, it established a safety evaluation index system of underbalanced drilling from five aspects, including people, equipments, environment, technology and management.The relative importance of index can be estimated experience from experts who have many years experience of this research area, and the weight can be calculated by soft yaahp combined with analytical hierarchy process.Selecting a certain underbalanced well, using fuzzy comprehensive evaluation calculate a result of safety level, which illustrates that some factors have a great deal influence on the final safety level.Picking five underbalanced wells as the samples and using gray comprehensive evaluation calculate the gray correlation of them. The smallest gray correlation show the lowest safety level and appropriate dangerous factors, which help people to find the real dangerous to rectify and control them.Finally, using fault tree method to draw the fault tree of underbalanced drilling blowout that can reveal important factors that might lead to blowout.