How to Evaluate the Effect of Mud Cake on Cement Bond Quality of Second Interface?

Abstract

Abstract A set of HPHT core filter press and a special manmade core have been designed to simulate the bond quality of second interface of cement job, i.e. the bond status between borehole wall rock contains mud cake and slurry, mud cake has formed on the rock at HPHT conditions. The filter press consists of three parts: heating jacket, HPHT cauldron and core holder, and the center of special manmade core has been drilled a disconnected hole as filtration outlet of drilling fluid. The drilling fluid only can filtrate from the outer wall of the special core to that of inner wall and form mud cake at the outer wall when carrying out filtration experiment of drilling fluid, so this bond status is in agreement with downhole condition. Slurry bond mold has been combined with HPHT core filter press, a novel method for evaluating the bond quality of second interface of cementing has been developed, and the method has been used to measure the shear bond strength between manmade core and slurry. In order to verify the rationality of the method, it has been applied to evaluate the effects of three drilling fluids on the second interface after mud cake formed on the special core. High flow rate washing before cementing has been simulated to wash manmade core after HPHT filtration experiment. The study shows that the novel method is simple, scientific and rational, better simulates the bond status of cement-formation interface; the mud cake has a pronounced affect on the shear bond strength; this method has high applied value, and develops a good foundation for studying the effect of drilling fluids upon the bond strength of second interface quantitatively; high flow rate washing before cementing is helpful for improving the bond quality of cement to formation.