Development of Activators for Improved Mud Filter Cakes Containing BFS
 Neeraj S. Nandurdikar

 A series of experiments was conducted to study the influence of blast furnace slag (BFS) as a drilling mud additive in reducing the spurt loss and formation damage potential of a drilling mud. The effect of BFS on the depth of penetration of the filter cake (i.e. formation of an internal filter cake) was also studied.

 A partially hydrolyzed poly acrylamide (PHPA) mud was selected, and samples having BFS loadings of 0, 5, and 30 pounds per barrel (ppb) were prepared. Filtration profiles were obtained by conducting permeability plugging apparatus (PPA) tests using artificial cores. PPA tests were carried out at 200^°F and 2000 pounds per square inch (psi) differential pressure. A novel method of conducting a repeat test on a given core, after scraping off the external cake, was adopted to study the influence of internal cake formation.

 Filtration profiles were run for the different BFS loadings and the results show that the spurt loss is reduced from 247mL for 0 BFS to 48mL for 5ppb BFS and 22mL for 30ppb BFS. This translates to 80% and 54% reduction in spurt loss in going from 0 BFS to 30ppb BFS. The internal cake also accounts for 35% reduction in spurt loss for 5ppb BFS and more than 75% reduction in the case of 30ppb BFS.

 Permeability studies were also carried out to investigate changes in the permeability of the cores after the PPA tests were conducted.

 These results maybe useful for the design of drilling fluids which not only have lower formation damage potential, but also have improved sealing capabilities for micro-fractured formations.