Use of Activated Charcoal in Cement To Combat Effects of Contamination by Drilling Muds

Abstract

Abstract Results of laboratory investigations of the effects of drilling muds on oilwell cements are presented which show that relatively large quantities ofuntreated muds do not seriously interfere with the setting of cement slurries, but that relatively small quantities of treated muds seriously retard thesetting of cement slurries. Laboratory results also indicate that the harmfuleffects of contamination with treated muds can be counteracted by the additionof activated charcoal to cements. Also described is the successful use ofcement containing activated charcoal for the placement of plugs in open holeafter previous attempts with ordinary cement had been unsuccessful. Introduction The contamination of cement slurry by dilution with drilling mud has longbeen considered a cause of failure in oil well cementing. The cement slurrymust displace the drilling mud from the annulus between the casing and thewalls of the borehole, and it is probable that some mixing of the slurry andthe mud occurs even under the most nearly ideal displacement conditions. Holeenlargement, failure to center the casing in the hole, and formation of gelstructure in the drilling mud increase the probability of contamination. Insome cementing operations, such as the placement of a cement plug in open hole, considerable mixing of the mud and slurry is likely. Many cement failures whichcan be attributed logically to no cause other than contamination of the cementslurry by the mud attest the need of a better understanding of thisproblem. Considerable attention was given to the problem of mud contamination ofcements about 20 years ago. The effects of field mud upon cement slurriesprepared with different amounts of mix water were investigated thoroughly, andthe data obtained were invaluable in determining the causes of the highpercentage of failure in oil-well cementing at that time and in bringing aboutimproved cementing results. Since then, many aspects of the problem havechanged, due primarily to advancements in cement and drilling mud technology.Today, several types of portland cement are used in well cementing and numerouschemical additives are used in drilling muds. An excellent report on theeffects of drilling mud additives on oil-well cements was issued during 1951 bythe American Petroleum Institute. Data in the report revealed that many mudadditives, notably organic materials in relatively small amounts, produce amarked effect on the properties of cements. Prior to this time, littleinformation has been available on the effects of chemicals commonly used in thetreatment of drilling muds upon the properties of cements. Another aspect ofthe problem of mud contamination of cements, which has received no attentionheretofore, is the possibility of producing a cement having propertiesunaffected by a reasonable amount of mud contamination. T.P. 3396