Water sensitive formations, mature fields, and relatively depleted formations can require complex fluid formulations using specific bottomhole assemblies (BHAs) and underbalanced guns fired to help minimize formation damage. Results have demonstrated that, in many cases where standard procedures were followed, production decreased and such procedures were not always completely effective. This phenomenon can be attributed to formation characteristics, such as kaolinite, smectite, silica incrustations, tertiary precipitations, pH changes, clay swelling, and others.
Relative permeability modifiers (RPMs) are being formulated and used within the oil industry to help mitigate such issues. Physically, the objective is to decrease the relative permeability to water without any (or minimum) modifications of relative permeability to oil. Basically, this methodology can be applied in water wet formations without oil permeability modifications. A standard procedure was executed in four wells and two different formations to prove this technique.
The technique involves using a standard BHA to clean and condition the well, after having selected the zone where the perforating guns will be fired. A specific formulation of RPM treatment is placed inside the casing using a balanced fluid placement technique in front of the section to be shot. This type of fluid has no salinity sensitivity and very low viscosity (less than 4 cp). After placing the RPM fluid, tubing must carefully be pulled out of the hole (POOH) to avoid disturbing and damaging this temporary plug. Guns are run into the hole(RIH) to the selected zone to be perforated after spotting the RPM and then fired, squeezing the system into the desired formations through the casing. The pressure limit must be related to the casing integrity and no more than 1,500 psi as closure pressure (10 min stabilization trend) is measured at surface, and then the final BHA run to begin production.
The primary objective of this paper is to present a non-damaging fluid that can be pumped (or gravity injected) through recently open perforations, reaching casing closure pressure, and changing nearby water permeability, without causing any completion fluid invasion into the formation or induced damage. This process can put the well into production immediately, without any additional cleaning fluid necessary for the removal of the RPM fluid from the formation. The treated wells experienced production with zero damage to formations.