Formation damage in the vicinity of the wellbore is a major cause of low productivity, and the difficulties involved in removing the damage translate into a significant number of wells that do not respond satisfactorily to remedial treatment. This damage is usually the result of fines migration which is triggered by the introduction of foreign water. The migrating fines tend to lodge in constrictions in the formation flow channels where they severely reduce production.
Clay stabilizers have been used to solve this problem for several decades. Cationic organic problem for several decades. Cationic organic polymers (COPs) have been the most popular polymers (COPs) have been the most popular stabilizers because of treatment longevity and effectiveness in moderate to high permeability formations. Most producing formations in the United States, however, do not have moderate to high permeabilities but are classified instead as "low" permeabilities but are classified instead as "low" permeability. permeability. A new clay stabilizing additive has been developed specifically for low permeability formations typical in the Appalachian basin. This low molecular weight chemical is shown to be effective in rock matrices with permeabilities as low as 0.015 md. Other popular clay stabilizers with higher molecular weights are less effective in preventing swelling and migration of clay in formations having permeabilities below 30 md. Additionally, permeability damage can result when these relatively high molecular weight polymers are injected into low permeability formations.
Data are included from laboratory core tests using the low molecular weight clay stabilizer. The encouraging results of these laboratory tests is supported by field production results in the Appalachian basin. The field data include the results of fracturing, acidizing, and other operations, all of which are tabulated and discussed.
The clays involved in the case histories represent clays typical to the Appalachian basin. These include kaolinite, illite, chlorite, mixed layer clays, iron oxides, and hydrous oxides. Generally, these clays occur in crystals of such minute size that they cannot be distinguished except by special techniques outside the scope of usual petrographic study. However, these minerals are very petrographic study. However, these minerals are very important volumetrically and greatly influence the way in which a formation responds to stimulation treatments. Specific mineralogies of these clays are listed in the appendix. The Ohio and Berea sandstones discussed in the Experimental Work section of this paper are commercially available sandstones, and the Clinton is a naturally occurring, oil-bearing sandstone. Brine permeability ranges are 0.01 to 0.015 md (Clinton), 0.15 to 0.50 md (Ohio), and 60 to 275 md (Berea).
In migration, clay minerals can be dispersed by contact with a foreign fluid, or they can be entrained by produced fluids and transported until a restriction (normally a pore throat) is encountered where the entrained particles bridge, forming a restriction to the capillary. The mechanism of clays and other fine minerals has been extensively explored in other sources.
Clay minerals are composed of small crystal structures that have highly negatively charged surfaces. In their natural state, the clays are surrounded by connate water that is highly saline in nature.