API TR 10TR4:2008 pdf download

API TR 10TR4:2008 pdf download.Selection of Centralizers for Primary Cementing Operations.
Acknowledgment
API Subcommittee 10 acknowledges the assistance from industry manufacturers in compiling this document. Manyof them provided photos of their centralizers,and those illustrations are included in this document.
1lntroduction
The proper centralization of the casing for primary cementing has long been a critical step in quality cementing. Lackof proper centralization can lead to severe cementing problems,including lack of zonal isolation and impropercasing support.The goal of this document is to provide the petroleum industry with information for three types ofcentralizers, their selection and application, and their advantages and limitations.
2Benefits of Centralization
When performing primary cementing jobs, the casing should be centralized in the wellbore for three reasons:
1. to help get the casing to bottom (this includes reduction of the potential for sticking of the string);2. to help move the casing during mud conditioning and during the cementing job;
3. to provide an optimal path for fluid flow during mud conditioning and cementing allowing for effective mud
removal to achieve zonal isolation.
Field experiences， numerous large-scale experiments and computer simulations have shown that poor casingcentralization can be detrimental to the cement job, particularly in narrow annuli. Therefore, a good centralizationprogram should aim for high levels of standoff, which produces improved mud removal, particularly across criticalareas of the wellbore,that is, those areas where isolation is required. lt is imperative the user investigate thestandoff at all points, especially between the centralizers.
2.1Definition of Standoff
Standoff is defined by APVISO documents (e.g. ISO 10427-2) as the smallest distance between the outsidediameter of the casing and the wellbore.The standoff ratio is defined by the same documents as the ratio of standoffto the annular clearance for perfectly centered casing expressed as a percentage (%)，Annular clearance forperfectly centered casing is the wellbore diameter minus the casing outside diameter divided by two. Figure 1illustrates standoff and annular clearance.