Chemical-Tracer Method For Testing Segregation in Multiple - Completion Wells

Abstract

As a means of testing segregation in multiple-completion wells, pressuremeasurements have a number of drawbacks and efforts to develop alternativeeffective methods have been generally unsuccessful. This paper presents achemical-tracer method which has shown good results in three field tests and isnow being patented. Its main advantages are that it: Introduction Development wells in oil fields having overlying, vertically spacedproducing zones are generally completed so that each zone can be producedindependently. However, these multiple-completion wells often present certaindifficulties. Faulty cementing of the casing in the well bore, failure of theproduction packers, corrosion of the well-bore tubing or the development ofvertical fractures adjacent to the well bore may permit substantial quantitiesof oil to flow between zones When this happens, any zone may be producingconsiderably more or less oil than the production figures would show. Such erroneous production data may result in the adoption of inefficientrecovery programs. Moreover, conservation regulations restrict the amount ofoil which can be produced from each zone of a multiple-completion well andimpose penalties in cases of over-production. This means that, to ensureaccurate production records, multiple-completion wells must be tested often todetermine whether adjacent zones are segregated from one another. Obviously, then, a reliable and practical method for making these tests is essential. Methods for Testing Segregation Pressure Method Multiple - completion wells are usually tested for segregation by varyingthe production rate from one zone and recording the pressure in another. Anypressure variation in the second zone generally means that the two zones arenot completely segregated. This method is reliable and satisfactory in mostcases. However, it is difficult to use where the zones have large productivityindices, because then even large quantities of oil may flow from one zone toanother without producing any significant pressure change.