API TR 10TR4:2008 pdf download
API TR 10TR4:2008 pdf download.Selection of Centralizers for Primary Cementing Operations.
1 Introduction
The proper centralization of the casing for pnmary cementing has long been a critical step in quality cementing. Lack of poper centralization can lead to severe cementing problems, including ladc of zonal isolation and improper casing support. The goal of this document Is to provide the petroleum industry with Information for three types of centralizers, their selection and application, and their advantages and limitations.
2 Benefits of Centralization
When performing primary cementing jobs. the casing should be centralized in the wellbore for three reasons:
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 f or 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 casing centralization can be detrimental to the cement job, particularly in narrow annuli. Therefore, a good centralization program should aim for high levels of standoff, which produces improved mud removal, particularly across critical areas of the wellbore, that is, those areas where isolation is required, It is imperative the user investigate the standoff at all points, especially between the centralizers.
2.1 DefinItIon of Standoff
Standoff is defined by API/ISO documents (e.g. ISO 10427.2) as the smallest distance between the outside diameter of the casing and the wellbore, The standoff ratio is defined by the same documents as tile ratio of standoti to the annular clearance for perfectly centered casing expressed as a percentage (%). Annular clearance for perfectly centered casing is the wellbore diameter minus the casing outside diameter divided by two. Figure 1 illustrates standoff and annular clearance.
