| oil-base mud cake which was bad for the cementing interface strength would appear on the borehole wall and wellbore casing When the oil-base drilling fluid was used to drill. Finally cementing interface strength and the quality of cementing would fall. Therefore, cleaning the oil-base drilling fluid mud cake was one of the effective methods to improve the quality of cementing.In order to produce thin oil-base mud cake on the borehole wall and wellbore casing, and from the perspective of effectively clearing the oil-base drilling fluid,, the removing and cleaning agent were screened according to the surface active function, at the same time, the methods of effectively cleaning the oil-base mud cake were discussed. Firstly, JCS, JCO-3, OME and the cleaning agents which include JCN-1, JCN-2, JCN-3, JCN-4, JCO-1, JCO-2, JCO-3 and JCO-4 were selected to add into the oil-base drilling fluid, doing the coupon experiment at the certain proportion. Removing mud cake ratio as the evaluation index, JCN-3 was the best Removing agent. Then JCN-3 and C2H5 OH were mixed according to the synergy of functional group in molecular, the influencing factors of mixed proportion and the total amount were researched through the coupon experiment. The result showed that the ratio of mud cake removed reached 90%, when the concentration of JCN-3 and ethanol was1:1 and the total were 2.2% of drilling fluid. Besides, the main performance of drilling fluid would not be significantly influenced by mud cake removing agent JCN-3/ethanol through testing the filtration, density, resistivity and funnel viscosity.In order to further improve the effect of removing mud cake, oil-base drilling fluid cleaning agent which was used to clean the mud cake and reduce its thickness has been developed. QXJ-1, QXJ-2, QXJ-3, QXJ-4 with water respectively, formed the cleaning agents,the mud cakes which were processed respectively by the mud cake removing agent JCN-3 and JCN-3/ethanol were soaked in the cleaning agent. The result indicated that the best cleaning agent was QXJ-2 and the concentration was 1% and 0.6% respective.On the basis of establishing the oil-base mud cake removing agent and cleaning agent,the use of both terms were investigated and the process of removing oil-base mud cake was determined through coupon experiment and cleaning experiment. The results showed that it would reduce the amount of adhesive on the bolt drilling fluid when JCN-3/ethanol agent at the proportion of 2.2% was added into oil-base drilling fluid at 55 ℃ for 40 min. Then the bolt on the adhesion of the drilling fluid was cleaned by QXJ-2 cleaning fluid with a concentration of 0.6% and temperature of 45 ℃ for 20 min, the removing rate of mud cake could reach 90%. Indicating that the combined use of mud cake quell agent and cleaning agent can significantly reduce the amount of adhesive drilling fluid on the bolt, which benefits the formation of thin mud cake.Interface simulation experiment was carried out for further investigating the effect of mud cake removing agent JCN-3/ethanol and detergent QXJ-2 on the interface cementation strength. The results showed that adding 2.2% of agent JCN-3/ethanol to the drilling fluid and then cleaning the mud cake by QXJ-2 could make the cementing strength raised to 10.3 times, and the interface enhancement effect was remarkable. |
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