Preparation and numerical simulation of bentonite based microbubble gas drilling fluid
In order to minimize the occurrence of jamming during gas hole drilling and formation,a microfoam drilling fluid is developed with sodium-based bentonite as base material.Various foaming agent and foam stabilizer are tested in-lab for the influence in microfoam drilling fluid,including drilling fluid stability and mobility,and they are also evaluated for rheological property,high temperature resistance,coal powder resistance and acid and alkali resistance of drilling fluid system.Use numerical simulation to study drilling fluid carriage with coal powder.The experimental results show that sodium based and bentonite based microfoam drilling fluid has good foaming performance.It remains stable below 80℃,and has good erosion resistance to coal dust with mass fraction less than 10%.The rock debris settling rate characterizes that the drilling fluid has better rock-carrying ability than ordinary water.Numerical simulation study indicates that when the coal dust concentration in drilling fluid reaches 4%volume fraction,after 20 seconds stimulated drilling,average drill hole coal powder volume fraction will reach 4.5%.Coal dust volume fraction at hole bottom is around 15%.The exit of opening has denser coal dust concentration than the entrance.Under the same condition,improvement of flow rate and revolving speed can carry more coal dust and reduce the concentration in air.
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