A major problem in maximizing oil production potential is the maintenance of adequate mobility control and favorable permeability profiles within the reservoir. Currently, polymer systems are profiles within the reservoir. Currently, polymer systems are receiving a great deal of attention in this application, not only as viscosifying agents, but also as cross-linked/gelled water blocking agents. Traditionally, silica gel systems had been used for such purposes. They still offer advantages in situations where polymer systems are limited by degradation and syneresis or are polymer systems are limited by degradation and syneresis or are inadequate to shut off major thief zones.
This paper presents the chemistry of silica polymer gel systems. and reviews their properties, benefits, limitations, and methods of application. The properties such as gel time, strength, and shrinkage vary considerably versus the concentrations of reactants, the type of acidifying/selling agent used, or the particular reservoir environmental conditions such as temperature, particular reservoir environmental conditions such as temperature, salinity, hardness, and hydrocarbon saturation. Gels ranging from elastic to rigid can be made with set times varying from a few seconds to several hours. Inorganic acids and reactants such as CaCl2 or NaAlO2 tend to react quite rapidly. Organic reactants that slowly hydrolyze or oxidize give more gradual formation of gels. Most reservoirs that contain high salinity, hardness, or temperature environments tend to accelerate the gel formation.
Examples of these effects are presented for several silicate based systems. Also the gelation of silicate in the presence of organic chemicals is discussed. Information from the grouting literature is reviewed so that a complete picture can be presented on the use and application of silicate based water control and production methods. production methods
Introduction
Permeability variations and the production of excess water are common problems that need to be addressed when maximizing potential oil recovery. The application of silica gels to these potential oil recovery. The application of silica gels to these problems was recognized more than 60 years ago by Mills and problems was recognized more than 60 years ago by Mills and discussed later by Hurd. Corrective actions may need to be performed at nearly any stage of operations, ranging from initial performed at nearly any stage of operations, ranging from initial drilling of the well to the later stages of tertiary recovery. During the drilling stages, a thief zone may be encountered causing loss of mud circulation. During the initial production stage, action may be taken to prevent water coning from an underlying active aquifer. During the later stages, action to correct vertical conformance or improve injection or production flow profiles may be taken to extend the well's life and improve profiles may be taken to extend the well's life and improve recovery.
The aforementioned needs for permeability modification require the injection of chemicals into the high permeability zones of the reservoir, generally only in the near wellbore area. By achieving either partial or total blockage of the pores, fluids are subsequently diverted into the less permeable unswept portions of the formation thereby increasing production.
The two systems that are most commonly employed are polymer and silicate treatments which form gels or cross-linked products after a predetermined period of time following penetration into the formation. Such treatments feature rather small investment costs and rapid payback in comparison to conventional EOR projects. In addition, they provide various associated tax advantages. Both the polymer and silicate systems offer certain advantages and polymer and silicate systems offer certain advantages and disadvantages.
Several forms of sodium silicate gels have been successfully used in each of these applications.
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