Improving Oilwell Stimulations With Compatible Oils

Abstract

Abstract Crude oils, diesels and similar distillates are often considered to be inert stimulation fluids for use in oil wells. In fact they may contain or create plugging materials which can reduce or destroy permeability. It is common knowledge chat produced crudes may contain clays, fines, sulphur, salt, organic debris, asphaltenes, as well as any chemicals added to assist production. Although crudes are still used to hydraulically fracture wells because of low cost, distilled oils are commonly used in an attempt to avoid the mentioned problems. However, clean fluids such as diesel and condensate are still incompatible with some crudes and particularly the asphaltic crudes common in western Canada. Special refining can produce oil which is very compatible with, crudes. One such oil is available at a cost comparable to diesel and has been used as a workover fluid, fracturing fluid, and acidizing spacer. Results of more than one year of field evaluation confirms that the fluid is practical to use and is meeting our expectations. Laboratory results and theoretical background are also provided. Introduction It is the intention of this paper to discuss some important aspects of the use of oils in well completions. Most ideas are relatively familiar to many readers, however, they will be reviewed in reference to a new product which has become available. In the majority of cases oil is used because of concerns over formation damage. In such cases, oil is often regarded as relatively benign in comparison to water-based fluids. There are many good reasons to believe this. The main ones are listed as follows:—Fresh water in contact with any smectite clays in the formation will be absorbed into the clay structure and cause swelling. The swelling restricts the pore throat to reduce the permeability.—Kaolinite clays and other migratable fines which are water wet or are loosely attached to the pore surface will only move within the connate water phase. When water invades a formation with irreducible water saturation, the fines will then become movable and begin plugging the pore throats.—Water, being the most universal inorganic solvent known, can carry a variety of chemicals, cations and anions into the formation. Incompatible water, sometimes even with very low concentrations of contaminants, can cause a variety of precipitates, emulsions and sludges which can reduce or destroy the formation permeability.—Even a very low percentage of fines contained in water can easily plug perforations or the formation. This point can more easily be appreciated since very dirty water is recognizable with the naked eye. It should be kept in mind that occasionally clear water contains enough fines to do serious formation damage. In contrast oils are perceived, although sometimes inaccurately, to have the following behavior:"Oil does not react with smectite clays to cause swelling. Further to this, oils are not expected to react with any clays present to produce detrimental results. ""Oil does not open the door for lines migration to begin. "