Laboratory work has shown that pipe dope, routinely used during well construction can penetrate and damage relatively high-permeability formations. Previous laboratory and field studies showed that dope-induced formation damage is severe (more than 99 percent). However that earlier work using cores up to 240 md demonstrated that dope particles would stay at the front face of the cores, forming a filter cake and not penetrate the rock matrix.
If the well is put on injection service and in the case of workovers such as matrix stimulation treatments, the formation damage caused by pipe dope will almost guarantee operational failure. However, for production, the dope can be readily swept to the surface and its impact would be minimal.
What would be the situation in higher permeability rocks if dope particles were to penetrate the formation in which case they may not be removed through flowback?
The objective of this work is to evaluate the magnitude of formation damage by pipe dope in higher permeability sandstone samples of 1,000 md in two injection tests of commonly found concentrations in field operations.
Results show clear penetration of the core matrix, manifested by large pressure gradients measured along the core. The dope, although in relatively small concentrations causes a considerable permeability reduction and, implicitly, a marked reduction in connected porosity. The latter is particularly important because small quantities can cause very large damage, unlike drilling mud which would require large losses into the rock to cause comparable damage.
The good news is that dope-free connections for casing & tubing can be used to avoid thread compounds and eliminate well damage as they produce zero effluents. Dope-free connection can also improve the efficiency and reliability of the operation itself, removing a cumbersome, albeit routine job, a major advantage in drilling operations. Because of obvious economic considerations these benefits will be more profound in a deepwater environment.