A technique for improving stimulation fluid recovery has been developed in the laboratory and has proven effective in field applications. The method involves improving proppant pack drainage and minimizing capillary pressure in the formation through the judicious application of surface active agents.
The technique is particularly applicable in low pressure oil wells and tight gas reservoirs, and may be used in all aqueous fracturing treatments. These include slick and gelled water, as well as foamed and crosslinked systems. The technique involves the use of a solvent in the pad fluids and a surfactant system throughout the pad fluids and a surfactant system throughout the entire fracturing treatment. This combination improves sand pack drainage and minimizes capillary water blocks in the invaded formation, while maintaining the water-wet condition of both the proppant pack and formation.
The results of field applications using this technique have shown great improvement in the recovery of aqueous stimulation fluids in both sand and limestone formations. Increases in initial hydrocarbon production have also resulted. Case histories are presented from both oil and gas wells in a variety of formations.
Much has recently been published regarding the mechanisms which cause load water retention and the techniques which may be employed to improve load water recovery.
The effectiveness of an aqueous fracturing treatment, as evidenced by increased hydrocarbon production, is often related to the amount of production, is often related to the amount of stimulation fluid recovered. However, when the factors affecting oil-water relative Permissibility relationships are examined closely, it becomes apparent that maximizing both hydrocarbon production and load water recovery will not be production and load water recovery will not be easy to accomplish. The relationships observed by Owens and Archer show that effective oil permeability, and therefore oil recovery, is permeability, and therefore oil recovery, is highest when the substrate is strongly water-wet and when water saturation is low. Conversely, a strongly oil-wet substrate and low oil saturation result in high relative permeability to water and enhanced load water recovery.
How, then, can load water recovery and hydrocarbon production be maximized by the save system? It would appear that the practical solution to this problem would involve a compromise between the two extremes. This paper presents an empirical investigation of this presents an empirical investigation of this problem. problem. In the early 1970's, water soluble fluorochemical surfactants were used successfully to help provide more rapid and complete stimulation fluid recovery. These surfactants were particularly successful in the low Permeability gas sands of West Texas and Eastern Permeability gas sands of West Texas and Eastern New Mexico.
The theory behind this application is that the ultra-low surface tension provided by these surfactants will help reduce capillary imbibition of injected water in the formation at the fracture face. Fluorosurfactants are still widely and successfully used in many oil field applications, and research continues in this area.
One of the major problems with fluorosurfactants is their inability to function effectively over a large surface area because of adsorption. All surfactants (" surface active agents") tend to adsorb, or plate-out, on solid surfaces to varying degrees. This problem can be especially noticable with fluorosurfactants, which are normally used at very low active concentrations.