关键词: 碳酸盐岩, 硫化氢, 气侵, 早期识别, 压力随钻测量

Abstract:

When drilling marine carbonate reservoirs, it is difficult to identify the early gas cut in reservoirs with fractures and pores due to the complex flow resulted from the substitution effect of wellbore fluid and formation fluid. Based on the models of gas cut in the drilling processes, this study discussed the mechanisms, occurrence conditions and interconnections of different gas cut models. New thoughts and methods were proposed for qualitative and quantitative analyses of S-containing gas cut in a direct invasive model. The upward migration and expansion patterns of gas along the wellbore were further investigated. During the upward migration process, the closer to the wellhead, the severed of gas expansion. Accordingly, the variations of the bottom hole pressure during the gas cut process were simulated using a multi-phase flow model that took into account the effects of gas-oil phase changes in the wellbore. It was shown that during the early gas cut, the bottom hole pressure fluctuated in the deep slim holes, with small increases followed by decreases. Based on the annular-pressure-while-drilling system that provides real-time down-hole pressure information, a new method was proposed for identification and early warning of gas cut through comparison with the normal trend line. The application of such method will provide effective protection for safe drilling of complex carbonate reservoirs.

Key words: carbonate rock, hydrogen sulfide, gas cut, early identification, pressure measurement while drilling