| Four XC-Polymeric water based mud systems with different median particle sizes of the bridging additives were used to study the effect of particle size distribution and flooding time on formation damage. The experiment was conducted using Leak-Off experimental setup. An ultrasonic technique, a non-destructive method was implemented to measure depth of invasion by the drilling fluid filtrates and particles on Berea core samples. The results of this experimental work proved that an increase in the median particle size of the bridging additive would decrease the invasion depth and increase the return permeability. It is also observed that as flooding time increases, permeability impairment and invasion depth increased, which resulted in an increase of the skin factor. For all of the drilling fluid types studied, the largest invasion depth was observed in the first four hours flooding time. This is due to the absence of well-established, low permeable filter cake to protect the formation from invasion by drilling fluid filtrates and drilling fluid particulates down to colloidal sizes. In sizing particles in the drilling fluid system, it is important to consider not only the invasion of particles, but also the invasion of particulates down to colloidal sizes like the polymers. It is possible to achieve minimum formation impairment by properly sizing the particles, not only to minimize the invasion depth into the formation, but also to effectively filter out the smaller polymers and other colloidal particulates in the drilling fluid system. An example is presented at the end to show how this experimental work can be applied to a horizontal well. |
