Page 134 - 6634

Figure 6.39 - Drilling from a floater. (Courtesy

Vetco)

WELLHEAD SYSTEM

The subsea wellhead system run by the drilling vessel prior to installing the

TLP is an 18-in., 10,000-psi WP system (Fig. 6.40), modified to accommodate the

tieback system. The wellhead housing is a standard extra- long type except that the

landing ring has been moved down so more of the housing is exposed when it

lands inside the 30-in. housing. The 18-in. x 13-in. casing hanger inner profile is

the same as a standard 163/4-in. x 13-in. casing hanger, which allows the same

running tool to be used for both the 183/4-in. floater-drilled and 16-in. TLP-drilled

wells.

DRILLING RISER SYSTEM

Drilling with a surface BOP and high-pressure riser is a reversal of the

standard techniques used in drilling from a floating drilling vessel. With this

arrangement, a smaller, less complex BOP at the surface can be maintained and

operated more easily. The high-pressure drilling riser assembly is essentially an

135