Underwater Drilling and Completion Methods
Authors: McEntee J.R. , Geer R.L. , Collipp B.G. 
Published: December 2007

Exploration and development of offshore hydrocarbon accumulations underlying deep water greater than about 150 ft. have been restricted by the physical and economic limitations of conventional procedures using bottom-supported drilling and producing facilities. To overcome these difficulties, underwater drilling and completion methods and equipment have been developed for drilling and producing wells from floating platforms in potentially any depth of water without the need for divers or visual observations of the underwater operation. The techniques have been successfully demonstrated in the Gulf of Mexico. The well control systems used for drilling, completing and producing the wells are designed to be fail-safe, remotely actuated and installed on the sea bottom. Model test of drilling platforms indicate that a semi- submersible, triangular-shaped configuration suitable moored provides the most stable working surface for floating drilling operations.

The Problem

Geologists have long believed that significant hydrocarbon accumulations exist at deep-water locations. Unfortunately, current mobile bottom-supported drilling rigs are limited to about 150-ft water depths. Moreover, bottom-supported drilling and producing platforms appear to be limited to 300 to 400 ft. of water due to limited technology and unfavorable economics. To economically explore for and exploit oil and gas prospects in deep water, development of new techniques was undertaken by Shell Oil Co. in 1955.In defining the problem, the important aspects of deepwater drilling and completion were considered to be

underwater wellhead control systems, floating drilling platforms, production handling facilities, well maintenance techniques and instrumentation.

Moreover, these technical investigations required support from other areas of the company's research and development activities, namely:

oceanography and meteorology, and soil mechanics and structures. The purpose of this paper is to describe system components and procedures developed to meet the exacting conditions of deep-water operations.

Summary And Conclusions

The success of Shell's underwater drilling, completing and producing methods and equipment results from an over-all definition of the problem which has assured compatibility of all procedures and facilities. Further, thorough engineering and comprehensive land testing of complete assemblies are required to minimize economic losses due to equipment failure in the high-cost offshore environment and to achieve acceptable standards of safety. Wells can be economically and safely drilled in deep water from a floating platform using wellhead equipment located on the sea floor. All desired operations, surveys and tests have been performed successfully without divers or the need for visual observation. Wells have been drilled to over 13,000 ft into typical Gulf Coast geopressured strata overlain by 300 ft of water. An optimal design for a floating drilling platform is a suitably moored, semi-submersible, triangular-shaped configuration. A rectangular-shaped, bottom-supported drilling platform, "Bluewater", modified to operate as a semi-submersible floating platform has demonstrated the validity of the design criteria. Drilling operations have been carried on in 15 ft seas and partial operations continued in 28-ft seas with 65-mph winds. Wells have been completed under water with remotely actuated fail-safe wellhead controls located on the sea bottom which have been tested under simulated conditions to have a life of 60 years. Flowlines can be connected without divers, but additional development of materials for flexible flowlines in conjunction with steel or aluminum is necessary. Moreover, through-the-flowline production maintenance tools to control paraffin, measure pressures, place gas-lift valves, etc., are feasible and have been tested successfully. Studies show that production methods depend primarily upon local conditions, such as water depth, well spacing, bottom conditions, distance to land, pipeline availability and others, but bottom-supported production platforms appear economically attractive in water depths of 300 to 400 ft, with floating production platforms attractive in greater depths. Adequate instrumentation of wellhead and platforms must be provided to assure efficient and safe operations.

JPT

P. 595ˆ