The Design And Application Of Weighting Flushing And Spacer Fluid

Prepad fluid includes flushing fluid and spacer fluid, it is pumped before cementing operation in order to flush borehole, change the wettability of the casing to bond with cement slurry easily, improve the rheology of cement slurry, to prevent the cement slurry from contamination , the drilling fluid from flocculation. The prepad fluid has multi-function, such as isolation, flushing, thinning, buffering and so on. With the increasing exploration and development of oilfield, there are lots of problems during cementing operation, such as high temperature, long cementing well section, abnormal borehole diameter, contamination, low flushing efficiency, bad buffer action, low displacement efficiency etc. All these complicated problems restrict the improvement of cementing quality. And cementing quality is relative to successful implementation of subsequent drilling, completion, production and enhancement of oil recovery, relative to the exploration and development course of whole oilfield. By analyzing the mating technology of cementing and cementing quality, we know the flushing fluid and spacer fluid are weak parts in cementing operation.In this paper, the action mechanism of flushing fluid and spacer fluid is introduced. The present status and development trend of prepad fluid have been analyzed. The evaluation methods on flushing efficiency test, the displacement efficiency of spacer fluid, the rheological property, the stability, the compatibility of mixture and interface cementing strength test have been summarized. The properties of surface active agent, suspension stabilizer, dispersion agent, fluid loss additive, weighting agent, antifoamer were compared and evaluated. Ideal additives were chosen. The weighting flushing spacer fluid has been developed by combinating theoretical analysis with tests. The system was tested in some adjustment wells and deep development wells. The results showed the system has higher flushing efficient, better isolation effect, wider density range from 1.05 to 1.85 g/cm3 which can be adjusted freely, API water loss less than 50ml. It can be compatable with drilling fluid and cement slurry. It is helpful to improve interface cementing strength, without foaming phenomena. It is pumped easily and operated simply. The interfaces of the return drilling fluid, flushing fluid and spacer fluid are very clear, the migma section is short. The system is helpful to increase cementing displacement efficiency, improve cement job quality, prolong the life of oil wells and enhance the benefits of oil and gas field exploitment.