Abstract

A method and apparatus to test the annular seal of a casing string placed in a wellbore is presented. This method and apparatus, called the Annular Casing Seal Test (ACST), successfully measures the annular casing seal in the wellbore using a positive pressure test. Results presented document the experimental studies using prototypes under a variety of cemented casing conditions to determine the ability to detect effective and poorly cemented casing annular seals. When the interior of the tool is drilled out, an array of encapsulated bores is exposed, allowing pressure and flow communication between the interior and the annulus of the casing. Prototypes tested in experimental wellbores confirm the ability of the technology to detect casing annular conditions. A well-cemented casing annulus is easily detected, since the test pressure only encounters the annular cemented across the full circumference of casing. A poorly cemented annulus is similarly detected because pressure escapes the ports into the void in the cemented annulus. An important application of this method allows the annular seal at the surface casing shoe to be inexpensively and quickly tested, providing positive confirmation of the protection of the aquifer. This test is an improvement over the casing shoe test, which is in reality, a measure of formation strength and has demonstrated short comings in detecting poor cement jobs near the casing shoe in a variety of applications. This method is also an improvement over cement bond logs (CBLs), which are more expensive, time consuming, and do not provide a positive test of hydraulic isolation.

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