The paper demonstrates both converging and controversial laboratory results in potential application of silicone compounds (silanes, siloxanes and silicone oils and resins) to be used for restriction of water production in gas wells. The research program was extended to determination of surface and colloid chemical, rheological, hydrodynamic and retention properties of silicone-containing fluids in natural and synthetic porous media. Special attention was paid to the effect of different silicones on absolute, effective, relative and normalized relative permeability, and capillary and normalized capillary pressure curves. The complex survey has clearly shown that some silicone compounds, particularly in low permeable, tough porous media, drastically change the capillary forces, the spontaneous imbibition rate, and hence they offer a special option for delay of water break-through in gas/water systems. The comparison of different silicones provided sufficient information for development of a new technology which has been tested under field condition for restriction of water production in a tough, low permeable gas field (Algyö field, Hungary).
Gas production from gas fields and underground gas storage is usually accompanied by unwanted water production. The high water production often deteriorates the gas flow and recovery efficiency in wells operating in gas fields and hampers maintaining an environment compatible operation. Therefore, during the past decades intensive R&D activity has been launched to develop a viable method to cure the problem. The different methods, tested also under field conditions, can be categorized as follows:
Application of chain-like polymer (e.g. triblock polymers used by Pusch et al.1).
Injection or in-situ generation of weak polymer gels (Zaitoun and Kohler2, Zaitoun and Pichery3.
Application of alcohol-containing polymer solutions (Lakatos et al.4).
Treatment of wells with surfactant stabilized oil-in-water emulsions (Sobanova et al.5, Romero et al.6 and Stavland et al.7).
Injection of silicone microemulsions (Pusch et al.8 and Lakatos et al.9).
Hydrophobization of formation rock (proposed but not tested under field conditions by Dewenter et al.10).
As far as the mechanism of water abatement in gas wells is concerned the above mentioned methods can be subdivided into the following groups:
Irreversible polymer or gel adsorption on surface of the pores or capillaries and reversible conformation change of polymer coils or gel films attached to rocks.
Disproportional permeability modification which can be traced back to mechanisms 1).
Partial or complete zone isolation/blocking by high viscosity emulsions.
Wettability alteration (shifting the wettability towards the oil-wet direction) modifying thus the capillary forces in gas/water systems.
Driving force of the present studies was the obvious fact that earlier some elements of the mechanisms and laboratory observations were not fully understood and interpreted. Therefore, the risk of the field applications is still unacceptable for the operators and hence, the technology is not attractive and matured for a routine application at gas fields or underground gas storage. It should be learned, however, the following circumstances:
Hundreds of gas wells operating in gas field produce substantial amount of water.
Restriction of water production in gas wells represent a crucial and unsolved problem.
On account of the inverse mobility ration of gas/water systems the well known and widely used water shut-off treatments in case of oil wells can not be applied.
Restriction of water production in gas producing wells needs different theoretical and practical approaches.