The
APHRON
ICS™
System
The APHRON ICSTM fluid system changes the way fluid works. It is the only fluid that provides a variable density fluid downhole, and is able to create an automatic "at-balance" condition between the annular and formation pressures to stop invasion and movement of the fluid into the rock. The system has been used worldwide in high permeability sands, fractured sandstone, fractured limestone and dolomite, as well as fractured granite. It has proven highly effective in stopping losses and invasion while providing rapid cleanup and enhanced production.
The APHRON ICSTM system uses nitrogen-core aphrons that are encapsulated and stabilized with a polymer and surfactant blend. The encapsulated micro-bubbles are non-coalescing and can be recirculated. Aphrons are created within the mud system during the natural course of adding products and mixing the mud, without requiring injecting external air or gas.
Aphrons in the APHRON ICSTM system exist as independent bubbles of air encapsulated by a multiple-layer film. This film, which is the key to maintaining bubble integrity, allows the aphrons to function as a stable drilling fluid. A surfactant is used to produce the surface tension to contain the aphron as it is formed, build the multilayer bubble wall, and create interfacial tension to form a non-bonding network capable of bridging openings in permeable and fractured formations. In addition to the surfactants, aphrons must be stabilized with a high yield, low-shear-rate-viscosity polymer. This type of polymer viscosifies the water “lamella” that surrounds the aphron core and strengthens the bubble film so that the aphrons can survive for a long time.
The aphron micro-bubbles bridge and pack off at the formation openings of a permeable zone, but unlike solid bridging materials, they are deformable and capable of adjusting to bridge a fractured or vugular opening. The aphron/gel microenvironment can contain tremendous energy, which contributes to the observed bridging effect in fractured formations.
Aphrons possess physicochemical properties that make them distinctively different from conventional bubbles. Although they deform under pressure and shear like conventional bubbles, aphrons resist losing air when compressed much better than conventional bubbles. Laboratory experiments at downhole pressures have shown that with only a small pressure differential, “bubbly flow” of the aphrons occur, whereby the low-density aphrons rush to the fluid front and form a soft seal ahead of the liquid phase. This process does not work with conventional bubbles, because they cannot survive downhole pressures.
Another unique feature of aphrons is their hydrophobic exterior, which causes them to have low affinity for each other or for the mineral surfaces of rock formations. By contrast, conventional bubbles are water-wetting. Thus, aphrons resist aggregation and coalescence, which minimizes phase separation; furthermore, they do not stick easily to porous walls and they can be pushed out of a formation easily during backflow of produced fluid.
Aphrons at the surface typically range in size from 25 =m to 1 mm diameter. This allows them to be recirculated, even when solids-control systems are in use. Most will not be removed by fine-screen shale shakers or flowline cleaners, and they are not discarded through hydrocyclones or high-speed centrifuges since they have little mass. Finally, aphrons do not interfere with downhole tools such as MWD or mud motors, making them ideal for directional and horizontal applications. |
