Study on Wellbore Relative Humidity of Gas Drilling in Condition of Formation Water

Abstract

A lot of advantages exist in gas drilling such as increasing rate of penetration, protecting the reservoir and preventing leakage. However, complex condition downhole, as a result of formation water, is one of the important factors that hinder the gas drilling from being widely used. As the consequence of formation water getting into the wellbore when drilling aquifer, the relative humidity of circulation gas increase, and complex problems such as sidewall instability and obstacle of carrying rocks are caused downhole. Therefore, the mathematical model of relative humidity coupling wellbore temperature and pressure distribution is established in this paper, and the critical water content and relative humidity of the borehole temperature, pressure, gas maximum moisture content, relative humidity distribution, and dew point condition were obtained through numerical simulation. Research results show that: when the relative humidity of wellhead is higher than the critical relative humidity in the condition of dew point, droplets have been appeared in bottom, but the wellhead is less than the emergence. With the gas drilling being carrying out constantly, the formation water, cuttings and borehole wall interact with each other and lead to the occurrence of sidewall instability, obstacle of carrying rocks and other complicated conditions downhole eventually. This study provides an important guidance to avoid the complex problems downhole caused by formation water in gas drilling. There is an important significance to improve the construction safety of gas drilling.