Th!s pa?~r discussesfteld application of :schniql;es for preventingannular gas flew after ;ementlng. Includedare sectionsoutlfnirigatheory ?xplainingthe a,inular gas phenomena,a graphical >redictivetechnique,theoreticalpreventivemethods, md case histories, of actual field applicationsof these preventivetechniques.The theory'discussed in this paper is based J on analysisof laboratoryresearchconductedby t~e Texas A&M UniversityResearchFoundationand ExxonCompany,U.S.A. The resultsr~f this research Indicatethat annular gas flow after cementingis associatedwith a reductionin the effectivehydrostatic head exertedby a cement column during ics initialcuring period.A graphicaltechniquewhich predictsthe potantialfor annular gas flow after cementinghas been developed. This techniqueconsistsof a plot af depth versus hydrostaticpressureof the annular fluld columns and assumes that the cement slurry reverts to a fluid gradientequal to that of its nix water density. The estimatedformationpore pressure is then plottedon the same graph. Any differencesbetween the pressurevalues expressed by these plots providean indicationof the degree of overbalanceor underbalanceexistingbetween the annular fluid column and the formation.If the potentialfor gas migrationthrough the lightenedcement column is indicatedby the graphical plot, severalpreventivetechniquesmay be used for field applicaliion. Some of these techniques include: minimizingheight of the cement column, imposingsurfacepressureon the annulus, increasing annular mud density,adjustingslurry thickeningtimes, conventionalmultistagecementing,increasingcement mix water density,or modified cement slurries. " Each of these procedureshas been successful 1y utilized In the Gulf Coast area FOY both tubingless and conventionaltype completions. Referencesand ill@trations at end of paper, NTROOUCTfONAnnular and Interzonegas flow shortly after the tlacement of cement continuesto be a major problem msociated with cementingcasing and liners. These )roblemsare,of particularsignificancein abnormal n'essuregas wells and remedialmeasures to control ;uchflow often requirea major expenditure. Annular asflow has occurred behind protectivecasing, productioncasing, and linerson both inshoreand offihorewells. It is si nificantto note that these 7 occurrences are not unque to any single operatorbut !avebeen experiencedby the industryworldwide." -Dc im oennis c. hvim.
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