Methods of Early Gas Kick Detection and Well Control Risk Assessment in Deepwater Drilling

Abstract

Abstract Gas kick early detection and well control are the hotpots and difficulties in deepwater drilling, so this paper aims to establish methods for more accurate gas kick early detection in deepwater drilling, and on this basis, to evaluate the gas kick degree and killing risk, providing a new method for fine well control in deepwater drilling. The calculation model of wellbore annulus temperature and pressure in deepwater drilling was established, which was used to calculate the wellbore multiphase flow; The limitations of conventional gas-kick methods were analyzed by using wellbore multiphase flow calculation model. On this basis, the gas kick early monitoring method based on identification of gas-liquid two-phase flow in deep-water riser was proposed, and its applicable conditions and advantages were analyzed;Through the introduction of maximum allowable casing pressure and gas position, the design method of pit gain warning value for deepwater drilling was established and compared with the conventional methods. Through the analysis of relationship between gas position and pig gain under different conditions, the limitations of current pig gain monitoring method were analyzed. Examples showed that: for deepwater wells whose water depth was greater than 800 m (existing shallow gas reservoirs, or with medium-low permeability formations), the gas kick early detection method based on identification of two-phase flow in deep-water riser had obvious advantages. And the gas kick degree could be calculated in real time based on identification of two-phase flow in riser. The pit gain warning value calculated by the design method established in this paper was more accurate and reliable, and under the certain condition of well control equipment, through operating parameters and formation parameters, a more accurate and reliable gas kick detection could be carried out by using this method. Therefore, the pit gain warning value could be designed according to specific well or depth. The methods of gas kick early detection and well control risk assessment in deepwater drilling proposed in this paper could detect gas kick more accurately and previously compared with the conventional methods. At the same time, it achieved the real-time quantitative description of gas kick degree, which was conductive to improving gas kick early detection accuracy and reducing monitoring cost. It has broad application prospects with further improvement of theory and equipment.