Sometimes, a new perforated well can not deliver fluid at a certain rate which is predicted by correlating to other wells on the same horizon. It is necessary to compare the mud used in the well with the mud used in other wells. Maybe the solid content of the mud is much higher than the solid contents of other muds. Probably based on gamma ray logs, the reservoir clay content is higher. Or possibly, some agents in the mud precipitate solid during contact with formation fluid.
Pressure build up test is a good indicator to quantify the degree of damage around the wellbore. Skin due to limited perforation interval must be considered before concluding the degree of damage due to mud filtrate or solid invasion.
Changing the wettability of the damager is one way to remove the damage. Surfactants as a primary emulsifier to generate microemulsion are believed able to change the wettability of damager and reduce interfacial tension. Figure 1 shows an example of a test result in the lab depicting the decreasing interfacial tension (IFT) over time. Reservoir with a higher temperature requires less soaking time to reach low IFT. By soaking microemulsion, the damager will diffuse and mix with microemulsion. The microemulsion is also stable thermodynamically and homogenous macroscopically.
The microemulsion comprises surfactant (cationic, anionic and nonionic surfactants), non-polar fluid (oil), polar fluid (water) and optionally co surfactant, acid. An example of ionic surfactant and non ionic surfactant is alkali metal alkyl sulfates and alkyl polyglycosides respectively.
After soaking the microemulsion, the well can be unloaded using a PCP pump since PCP pump can handle very well the solid within the microemulsion.
Recommended reading, microemulsion application in hair drying, and an example of nonionic surfactant:
