During well design and construction, the cementing of tubulars into the wellbore, referred to as primary cementation, has always been a critical step because the introduction of cement into the annulus between the tubular and open hole provides zonal isolation. It is well documented by API, SPE and other industry publications that achieving a good cement bond depends on the proper selection and placement of centralizers onto the pipe being cemented. In addition, getting the pipe to total depth (TD) is one of the most important objectives in the well construction process. Proper placement of centralizers drastically reduces the effects of differential sticking of slick OD tubulars when running across permeable formations and increases the chance of getting to TD. Once at TD, centralizers play a very important role by aiding in mud removal, which allows the cement to flow into the proper position with minimal channeling. Solid expandable liners are most often run without centralization due to the very nature of expanding tubulars and the effect that the centralizers would have on the expansion forces. Another contributing factor is the tight clearances between the host casing and the expandable tubulars that are present in many applications. Adding to these challenges is the need for proper standoff to aid mud removal in the underreamed hole section in which the expandable tubulars are deployed. Solid expandable liners provide a drilling hazard mitigation technique covering pressure anomalies in the wellbore and their use in horizontal wells for maximum oil recovery furthers the importance of centralization for drag reduction, zonal isolation and the prevention of differential sticking. In this paper the authors will review the cementing process and the problems associated with centralizers and explore several novel, field-proven and developing approaches to centralizing solid expandable pipe using both positive standoff and bow- spring centralizers.
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