Well Cementing Replacement Flow Regime Selecting And Computing Method Of Coal Bed Gas

Coal seam has low mechanical strength and badly stability of mechanics.Duringthe Drilling Process,coal seam is vulnerable to collapse, producing irregular borehole;The design of the formula of the slurry is very difficult; there are more complexsituations in the process of cementing such as water mud will lost easily; Coal seamsvery vulnerable to injury that increases the difficulty of the protection of coalseams.Cementing replace efficiency directly affect the cementing quality,the life ofcoal seam gas and mining effect.So it's important to study the displacement efficiencywith different flow pattern and different well condition.Through the log data of Hemei1analysis showed that hole enlargement is veryserious,some well intervals'enlargement even up to60%.Using the Fluent softwaregets the simulation of displacement efficiency with different hole enlargement rateand different flow pattern(plug flow,laminar flow and turbulent flow the displacementefficiency of which are98%,92%and99%,when the enlargement rate is40%),it showsthat the displacement efficiency of laminar flow is the worst,and the turbulent flow'sis a little better then plug flow's.Because of the effect of hole enlargement in coalseam,In order to ensure the displacement iof turbulent flow,the critical pumping ratereaches8.145m3/min,the work progress is diffcult to be finished,and the annularpressure lost is high,it could easily cause the high pressure in the bottom of thewell,damages the coal seam.But when the critical pumping rate of plug flowdisplacement is only0.756m3/min,the work progress become easily,ensure thecontact time of slurry and strata and the low pressure,it is suitable for coal seam wellcementing.Then,use the Fluent analysis influence of displacement efficiency with theoperational mode of hole enlargement,decenter,well deviation and so on.This researchShows that, in the situation of plug flow, the increase of both the hole enlargement,eccentricity and deviation angle can reduse the displacement efficiency;the moredensity contrast is,the better replace effect is.