In the past 5 years, chemical profile modification for water injection wells has evolved from the experimental stage to a routine procedure. Chemical profile modification can be used under a wide range of reservoir conditions to treat a variety of reservoir heterogeneities known as thief zones. This paper presents a discussion of the typical thief zone problems, how they are diagnosed and the design process necessary for a successful profile modification treatment. Introduction Chemical profile modification has been practiced since the mid - 1940's when the practiced since the mid - 1940's when the South Penn Oil Co. treated 159 water injection wells on the Bingham 533 lease in the Bradford field. This project resulted in the recovery of 285000 bbls of incremental oil and a 63% reduction in water oil ratio (WOR). Since then, nearly every conceivable chemical and solid product has been evaluated for permeability product has been evaluated for permeability reduction. Several techniques have emerged and are marketed under an array of trade, generic and process names. Typically these treatments are performed turnkey as a specialized operation provided by an oil field service company. Profile modification (PM) treatments must Profile modification (PM) treatments must be designed specifically for individual wells based on all available relevant data. Usually, one chemical system can be applied to an entire field, although some fields may require a combination of systems. Gel slug design for a given well is a function of many variables:thief zone typethief zone location with respect to shale barriersinjection rates and pressuresmatrix permeabilityreservoir brine compositionreservoir and bottom hole temperaturesdegree of permeability reduction requiredvertical profile prior to treatment In order to achieve the highest rate of success, all of these variables must be carefully analyzed and used in treatment design. Once a treatment is performed, its progress must be monitored to insure the progress must be monitored to insure the maximum benefit is realized. Figure 1 is a flowchart outlining the process used to design a PM treatment. THIEF ZONE CHARACTERISTICS Several types of thief zone problems that reduce vertical sweep efficiency are encountered in water injection wells. The severity and type of thief zone must be diagnosed in order to select the best treatment design for a given well.

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