Overflow behaviors of natural gas kick well .with high content of H2S gas

Key words:  natural gas wells  gas kick  H2S  multiphase flow in annular  overflow

Abstract:

Based on hole structure and drilling behavior of a gas well which has a high content of H2S gas in Sichuan, the conservation of mass equations and momentum equations were established considering overflow characteristics of high content of H2S gas kick and H2S solubility in water. And the equations were computed by using finite difference approach. The results show that the solubility of H2S is greater than that of CH₄ at bottom hole, and H2S begins to separate at about 360 m away from wellhead. With the content of H2S increasing, the density change range increases during the gas going up, and the position of the gas dramatic expansion is close to the wellhead. When the gas kick volume is same at the bottom，the higher content of H2S, the greater gas expansion factor and pit gain, at the same time, the smaller gas volume fraction at the beginning, but greater when they reach wellhead, which increases the difficulty of gas kick detection and the danger of well control. The descent of bottom hole pressure,pit gain and shut-in casing pressure is smaller than that of pure hydrocarbon when high content of H2S gas kick happens, which can't truly reflect gas kick and the situation is getting worse with time. The casing pressure of high content of H2S gas kick during killing well has little difference to pure hydrocarbon, so applying certain pressure to wellhead can inhibit the expansion of H2S and slow down the blowout accidents.