CEMENTING PLUG

摘要

The invention provides a bottom cementing plug (594) which is releasably attached to a top plug (584) by means of a tubular sleeve (550) and shear pins (553). Instead of shear pins a shear ring, which may be segmented, and which is integral with the tubular sleeve, may be arranged. The tubular sleeve (550) comprises first openings (565) which are covered by burst plates (570) for allowing cement to pass after having set the plug on the float shoe at the casing bottom. The tubular sleeve (550) may comprise second openings (554) covered by burst plates (555) to allow the cementing process to be performed in case that the top plug has been launched together with the bottom plug. The invention further provides a dart launching device, where the darts are arranged in a sleeve coaxially with and radially spaced from the housing of the launching device. A fluid diverter is arranged at the top of the launching device for diverting the fluid into the annular space between sleeve and housing in order to prevent pressure overload on the plungers which hold the darts in place before they are launched.