Discussion On A New Method Of Curing Cake And Its Curing Mechanism

The mud cake is formed in the process of drilling fluid circulation on the wall, it can stabilize wall and ensure working fluid cycling smoothly. But in cementing operation, mud cake hinders contact between the slurry and the wall and impacts cementing effect of the second interface. Hence, it leads to disqualification of cementing and crossflow after getting into operation. Stratified injection can not be implemented and there is not effect of acid fracturing. At present, it is unable to clean up the underground mud cake completely, and the technology of mud solidifying still have some shortages. Therefore, in order to improve the quality of zonal isolation, we must explore new ways to eliminate the adverse effects of mud cake.In this paper, we try to develop a new technology to eliminate the adverse effects of mud cake. We design a flushing fluid system with a special chemical composition, then make it react with the active substance in the mud cake so that mud cake solidify in a short time and solidify with cement after injection into the slurry. Based on scientific experiments and material analysis, we explore the mechanism of eliminating the adverse effects by using flushing solidifying liquidWe select the common polymer sulfonated drilling fluid system in Tarim Oilfield and solidifying agents and penetrants in the market to do the experiments. We optimize the amount of the agent and penetrants and evaluate the effect of temperature and time on flushing solidifying liquid. In addition, we also evaluate the solidified effect of mud cake formed with different densities drilling liquid. Moreover we study the flushing solidifying liquid compatibility with the slurry. Laboratory experiments have proved the feasibility of industrial applications. Based on laboratory experiments and theoretical studies, the conclusions reached as follows:(1) It is preferable to regard solution contains10%sodium silicate,2%NaOH and5%CaCl2as a major component of the flushing fluidsolidifying formulations; solution contains0.6%of fatty alcohol ethoxylates and0.4%sodium dodecyl benzene Sodium is the main penetrant. They are added into the flushing solidifying liquid to increase the efficiency of the curing reaction;(2) As the increment of curing temperature and the the extention of curing time, bonding strength between mud cake and cement increases and till the fifth day,it achieves maximum and dose not change any more;(3) the flushing solidifying liquid has no effect on the flow of the slurry, but it can shorten the mixed slurry thickening time and reach the request of the project by adding a retarder; after treat by flushing solidifying liquid, mud cake formed by different density drilling liquid have the ideal solidifying effect;(4)It can be found that there is not any cracks by SEM, junction interface cementation is in good condition and no obvious crack on the solidification surface can be seen. It is discovered that the mud cake. generate a new phase of calcium silicate hydrate (C-S-H) and hydrated aluminum silicate through XRD diffraction. These gelling material have effect on the various substances in mud cake, thus the whole cementing interface is solidified;(5) Results of the experiments show that a series of hydrated calcium silicate gel (C-S-H) produced in mud cake solidification reaction link with the hydrated calcium silicate gel formed in the hydration of cement. A network structure in the interface and inside unifies the mud cake and cement, so as to form a dense body, for achieving the purpose of eliminating the negative effects of mud cake.