Most water-based reservoir drilling fluid systems used today are comprised of four primary components: the base brine, viscosifier, fluid-loss additive, and bridging particles. With the exception of minor adjustments of loading levels, the first three components normally do not change. The two primary types of bridging agents include calcium carbonate and sodium chloride salt. Some companies offer as many as seven different grades or sizes of each type of bridging particle.
For the first time, the "ideal" pigment-size-distribution theory used widely in the paint industry has been transferred to practical oilfield use. This paper discusses the method and its use in selecting the optimum blend of bridging particles, focusing on an ideal packing sequence for minimizing fluid invasion. The authors examine the various procedures for optimizing sealing, as well as a management maintenance system.
The paper expands on Abrams’ Median Particle-Size Rule by going beyond the size of particle required to initiate a bridge. In the discussion, the authors examine the ideal packing sequence for formulating a minimally invading (non-damaging) fluid.