Study On Water - Carrying Water In Gas Drilling

Gas drilling belongs to underbalanced drilling. It can improve ROP、reduce well leakage、reduce drilling costs and improve well production and EOR. Thus, gas drilling has been widespread attention at home and abroad. However there is little research at home and abroad about carrying water while gas drilling. The main direction of research focused on gas carrying rocks. Most studies converted formation water into equivalent ROP and did not consider the impact of physical properties of the liquid、water film and droplets in the annulus. This thesis will build gas drilling wellbore flow model and annulus carrying water model, and combine gas dynamics, gas-liquid two-phase flow theory and droplet dispersion theory to research the law of carrying water while gas drilling in detail.This thesis has analyzed the effects of formation water on gas drilling and researched water-carrying mechanism of the gas-based drilling technology, such as air drilling、mist drilling and foam drilling. For the problem of carrying water while gas drilling, this thesis has combined gas dynamics theory、fluid dynamics theory and the actual situation to establish the mathematical model of gas flow in the wellbore while gas drilling. This model has taken the variation of gas physical parameters and bit pressure-drop into account. Then, this thesis has studied the gas-liquid two-phase flow pattern in the vertical annulus, and thought the annular flow was the effective flow pattern while carrying water. Combined the gas-liquid two-phase flow theory and the annulus structure characteristics, and considered the water film on the annulus wall and the content of droplets in the gaseous core, we have established the mathematical model of annular flow in the annulus and tested this model by a visual simulation experiment. At the same time, this thesis has studied the dynamic rule of droplets in the annulus, and built the calculation model of the droplet size, as well as analyzed the influence factors of droplet size and droplet size distribution and morphology.Combined gas flow model in the wellbore while gas drilling with annular flow model in the annulus, the carrying water model while gas drilling has been built and calculated by Mathcad. Through the calculation of example, the distribution law of pressure、water film、 droplets and fluid parameters in the wellbore after the water output while gas drilling has been analyzed. At the same time, the influence factors of carrying water while gas drilling have also been studied, including annulus structure and fluid physical properties. The studies show that the bigger annulus area is not conducive to carrying water and the smaller surface tension is conductive to carrying water. At last, the variation of carrying water after adding atomized liquid while gas drilling has been calculated by the carrying water model. The calculation results show that atomized liquid is conducive to carrying water.