Poor productivity of promising new wells or old wells with workovers can often be traced to undesirable characteristics of the borehole fluid used in the completion.This paper presents laboratory and field results(see table 1)that show clear examples of productivity losses,resulting from completion damage sustained during workover jobs.For these specific jobs,diesel,calcium chloride and filtered seawater were used as completion fluids.The production rates after the repair jobs suggested that calcium chloride and filtered sea water are more damaging(productivity loss up to 100%)and diesel was less damaging(productivity loss up to 48%).Laboratory work was initiated to evaluate the wellbore damage that occurs during initial well completion or workover operation.This lab work included the examination of the mineralogy and texture of the selected core samples by using conventional core,thin section and x-ray analysis.Also included were”return permeability test”results.Several results are obtained from this study.First,the mineralogy and texture of the selected core are chemically and mechanically stable.Second,solids in the completion fluids appear to be the major cause of the productivity loss in the tested cores.Third,in oil wet type reservoir,use of water base mud in drilling or working-over a well,result in a trapped residual saturation.
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