Abstract
Fluid loss control is often a consideration, if not a major engineering exercise, for a wellbore workover or completion operation. When the mix includes high bottomhole wellbore temperature, high reservoir pore pressure and high reservoir permeability and porosity, then the well killing operation can become very complicated. For these reasons many operations include mechanical means of fluid loss control, thereby achieving positive well control for a long period of time without the worry of reservoir damage by fluid invasion and kill fluid byproducts. However, there are some instances, such as tripping drill pipe or tubing in or out of a well, that mechanical tools are not applicable.
Enter chemical fluid loss control. Often referred to as "fluid loss pills," chemical fluid loss control has been associated with everything from shredded newspapers to the latest biopolymers, which may carry carefully engineered bridging solids. While completion operations will hopefully not use bridging solids usually reserved for lost circulation while drilling, the point is that just about everything at hand on a rig location or in a laboratory has been tried as a fluid loss control agent.
For most of these chemical fluid loss pills, the upper limit of endurance is 275°F (135°C), which is the melting point of processed starch commonly found in fluid loss pills. Also, most commercially available fluid loss pills lose temperature stability as fluid density is increased with water soluble salts. A new fluid loss control pill has been designed to provide effective fluid loss control for 24 hours at 300°F (149°C) in a fluid density up to 12.5 pounds per gallon (1.50 specific gravity).
