Study On Sealing Spacer Fluid System Suitable For Shale Formation

There are a large amount of microcracks which are open in shale formations especially in its hard brittle part, clay minerals there have a strong ability of hydration and expansion, which can lead borehole peeled and collapse. This article mainly studies on a sealing spacer system think about wellbore stability and reservoir protection. This system can form a dense sealing layer pressed against the borehole wall, reduce spacer and cement slurry filtration and prevent borehole collapse. Also it can improve the loading capacity of shale formation.Optimize the admixtures of the sealing spacer system through comprehensive assessment of API filter loss test, stability test, rheological test and flushing efficiency test, such as film-forming agent, suspending agent, and surfactants, etc. Determine two kinds of sealing formulas which apply to different temperature ranges and then determine two corresponding sealing spacer systems by controlling variables method. The system studied with good rheological property and suspension stability can control its leak-off volume within a lower value, also it has good compatibility with drilling fluid and cement slurry commenly used in shale formation.This paper estimates the sealing property of the spacer system through measuring permeability of filter cake and artificial core polluted test and breakthrough pressure test. The results show that the sealing spacer system for shale formation is of wide range of density and good thermostability. It can plug microcracks in shale formation and at the same time form a dense sealing layer on the surface, which can improve the loading capacity of shale formation effectively In a word, the system is of significance to borehole wall stability in in shale formations especially in its hard brittle part, ensuring construction safety and cementing quality.