Development, Application, and Utility of Compact Wellhead Systems

Abstract

The use of compact wellhead systems, with the ability to hang multiple casing strings from a single forging, has improved drilling efficiency in the Gulf of Mexico, Offshore Louisiana. This recently patented dual hanger system is being used to substantially reduce the drilling cost and improve safety. Both an 18-5/8″ OD (Outside Diameter) conductor casing assembly and a 13-3/8″ OD surface casing assembly are installed through the diverter assembly and supported within the dual hanger casinghead prior to any disconnection and removal of the diverter assembly. An upper compact housing is then utilized and both a 9-5/8″ OD protective casing assembly and a 7″ OD production casing assembly are installed through the BOP (blow out preventer) assembly prior to any disconnection and removal of the BOP assembly. Compact wellheads have been utilized on several development drilling projects with standardized casing programs for several reasons: –Time and money were saved as a result of the reduction in BOP nipple up time.–Significant safety advantages were realized; the use of mandrel hangers resulted in immediate sealing of the annulus in an area where annular gas flow is prevalent.–Casing cutting can be eliminated, thereby, minimizing production shut-in time during PWD (Produce While Drilling) cycles. As of January 1, 1989, Shell Offshore Inc. (SOI) has installed 40 compact wellhead systems on two recently drilled development programs. The total cost savings directly attributable to this system, to date, is $511,000. This paper will address the pros and cons using these wellhead systems, modifications implemented, and review operating experiences to date. In addition, suggestions are presented for further development and use in both low-pressure and high-pressure applications.