Research On Well Control Technology For Safe Tripping

At present, with the structural adjustment of domestic energy consumption and theurgent need of environmental protection, the natural gas which is the most clean andlow-carbon fossil energy will play a key part in today’s market. However, with theincrease of reinforced exploration of natural gas, the problems of overflow, well kickoccurred frequently, especially in the part of the gas field in Sichuan field. The gas wellis accompanied by high pressure and high sulfur usually. It is not only increased thedifficulty of the drilling operation, but also a major challenge for well control safety.Tripping is the most difficult condition in overflow of drilling. In recent years, the gaswells in east Sichuan region often cause overflow during tripping operation. It not onlyeffects the safety of drilling operation, but also makes economic benefits bad as well asbring casualty. So it is an urgent thing to study the well control technology for safetripping which has great significance for solving practical engineering problems andenhancing the level of gas well control technology for safe tripping in China.This paper which is based on the summary of characteristics of the well controltechnology of drilling at home and abroad did a deep research from several key aspects,including the mechanism of gas channeling, gas channeling critical height, rate of gaschanneling, gas tripping speed control and drilling fluid density in relevance to therheological properties.On the condition of known formation and the normal polysulfide drilling fluidsystem in east Sichuan region. This paper found the correlation between drilling fluidrheological properties and density through the method of experiment and the statisticsof field data, and built mathematical model of the relationship between density andrheological parameter.Through the real gas state equation, combining the conventional drilling fluidmodel of gas spillover and considering the gas slippage, transport, expansion in theannular, determined the critical height of gas channeling.According to the gas liquid two phase flow theory, this paper found the mainfactors influencing the rate of gas channeling. This paper on one hand made reasonableimprovement on the basis of conventional method using drilling fluid performanceparameters which can calculate the rate of gas channeling though vertical depth, drillingfluid density, plastic viscosity and surface tension, on the other hand used field data amending the theory so that it can make the result more accurately. Therefore, thismethod can predict the rate of gas channeling in advance and do not need after effectingtest. So it can provide the basis for the actual safety operation.According to the principle of balance of bottom hole pressure as well as the impactof fluctuating pressure, the maximum speed of tripping can be determined in the gasformation, which can provide theoretical basis for site for tripping operation.According to the related data of east Sichuan gas wells, a safe trip applicationsoftware has been programmed which can provide theory basis for field operation andoffer a convenient calculation tool.