Myth-Busting Performance Properties of Nonmetallic Rigid Centralizers

Abstract

Performance characteristics of nonmetallic rigid centralizers are not defined under the API 10D, Methods for Testing of Solid and Rigid Centralizers. API Technical Report 10TR5 defines recommended performance tests for rigid centralizers, but does not describe testing for coefficient of friction or wear loss. Selection criteria are often based on manufacturer's test methods, material supplier data sheets, and end-user experience using various materials and designs. While American Society for Testing and Materials (ASTM) testing methods are available to measure mass loss caused by wear and frictional coefficient, the selection of the test method that provides the most accurate data replication use in a wellbore is proposed.

Rapid advancements in the mechanical properties of composite materials have given manufacturers a multitude of material choices. However, comparative data based on standardized testing is inconsistent throughout the industry. Not only should consistent test methods for wear and coefficient of friction be established, but resistance to load-at-temperature should also be a criterion for measurement. Because of a lack of an industry standard testing protocol during product development, a standardized method was generated to best replicate the performance characteristics required for downhole conditions.

Various ASTM test methods are deployed in the qualification of rigid composite centralizers, which yield a wide array of results attributed to the inconsistencies of test apparatus and conditions of testing. Through trial and error, a best practice was established for the qualification on nonmetallic rigid centralizers that resulted in more accurate measurements of wear and frictional coefficient. However, friction factor and wear resistance are not the only attributes for durable centralizer requirements to effectively run casing to the target depth. In some instances the casing may need to be retrieved from the wellbore. Other factors such as the ability to rotate the casing string at a prescribed temperature and load rating need to be tested and fully understood. By standardizing the test method for nonmetallic centralizers, the mystery regarding their performance is more clearly understood. The proposal is for lessons learned during product development to be considered for adaptation in API 10TR5.

The rapid advancement of new types of composite materials and the ability to measure their performance properties in downhole conditions will lead to further cost-effective product innovations.