An Experimental Study of Mud Displacement in Primary Cementing

Abstract

Displacement of mud by cement slurry was investigated with a plastic model of annulus which was 4m tall, 52mm ID of outer pipe and 34mm OD of inner pipe. By the direct observation of the outer surface of cement, the height of cement head was determined. The ratio of this height to a calculated height obtained by the injected amount of cement slurry was used as an index of experimental results. As factors to determine the mud displacement, were selected both the density differential between mud and cement slurry and the ratio of apparent viscosity of both fluids under flowing conditions. Results obtained were as follows: (1) Effect of pipe position in case of the two factors kept properly: whereas the ratio of height was more than 0.8 in experiments using a concentric annulus, it decreased to about 0.7 in experiments using a eccentric annulus (50% standoff). (2) Results in a concentric annulus: although always good results could be obtained for the density differential of above 0.4g/cm3, the viscosity ratio had to be kept 4-5 for the density differential of 0.1-0.2g/cm3. (3) Results in an eccentric annulus: it is more important to control relative flow properties between mud and cement slurry, and for density differential of 0.5g/cm3, the viscosity ratio of about six was necessary to obtain a good result.