The possibility of causing formation permeability damage exists during many operations throughout the life of a well. This paper deals with formation damage in only the earliest stages, i.e., during drilling and completion. Drilling fluid is the first non-indigenous fluid to contact the formation and thus, it provides the first opportunity for causing permeability damage. Other potentially damaging fluids that frequently contact the formation during drilling and completion are cements, perforating fluids, gravel packing fluids, and kill fluids.
Most drilling fluids are designed to de-flocculate clays and other fine particles in the wellbore, which is opposite to what is desirable in the formation rock. Therefore, filtrate invasion is potentially very damaging to the rock in the near-well area. Potentially damaging filtrates are also lost to the formation during well completions. Permeability damage frequently extends a few feet into the formation which makes it difficult to remedy. Therefore, damage prevention is very important.
Damage prevention is best accomplished by both minimizing filtrate invasion and the detrimental effects of invasion. While both are important, the latter is more practical because total elimination of filtrate invasion is virtually impossible. Water-based drilling and completion fluids can usually be made non-damaging by assuring that (1) they contain an adequate amount of salts, especially potassium salt, (2) they have a pH lower than about 9.5, (3) they do not contain materials that form precipitates on contact with formation water, (A) they contain a minimum amount of de-flocculants, and (5) completion fluids are clean. Laboratory flow tests using formation rock and reservoir fluids are useful for maximizing efficiency and effectiveness in the fluid design. Maximizing productivity of a damage susceptible well comes about only through a concerted effort to prevent formation damage during the life of the well, especially during drilling and completion.