Design and development of superior drilling and drill-in fluidsand also assessment of the effectiveness of mudcake cleaningfrom the borehole wall by cleaning systems require a goodunderstanding of the fundamental phenomena associated withthe erosional behaviour of mudcakes formed by different mudsystems. Because of serious consequences of mudcake erosionon formation damage potential of drilling muds and mudcakecleaning prior to a cementation job, it is important to have asuitable, simple and field applicable method for predicting theerosional potential of mudcakes formed by muds of differentchemical composition. The prediction of erosion behaviour isessential to screen and select appropriate mud additives andalso to design new mud products for producing good qualitymudcakes on the borehole wall. The technique and technologycould provide a suitable means to assess the effectiveness ofmudcake cleaning systems and help design such cleaningsystems for removal of mudcake from the borehole wall.Cakes formed by several water-based muds were evaluatedusing the newly developed technique. The testing has beenperformed with the simulation of hydrodynamic conditionscorresponding to the drill collar-borehole annular section of awellbore. The results indicate that the presence of electrolytesignificantly increases the erosion coefficient of bentonitemudcake. Ionic fluid loss additives such as PAC (polyanioniccellulose) and CMC (carboxymethyl cellulose) reduced theerosion behaviour of salt water-based bentonite mudcakesignificantly. However, the presence of polyanionic fluid lossadditive PAC caused a drastic reduction in the erosioncharacteristic of NaCl-based salt water mud compared to thepresence of anionic fluid loss additive CMC. The presence ofnon-ionic fluid loss additive, modified starch shows littleimprovement of erosional behaviour of salt water-basedmudcake. It seems to be that the electro-chemical forces ofinteractions of ionic fluid loss additives play a vital role inmaking a mudcake non-erodible. The variation of the erosionalcharacteristic of the mudcakes is attributable to the physical,chemical and electrical properties of the cake forming mudadditives and also the nature of the fabrics formed by theseadditives within the mudcake matrix.
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