A New Completion System for Surface-Controlled Subsurface Safety Valves
Authors: Hill T.H. , Gordon J.R. , Warner D.G. 
Published: December 2007

This system uses the annulus between concentric tubing strings for hydraulic communication. Small-diameter control lines are eliminated, thus allowing the use of surface-controlled valves in tubingless as well as in conventional completions and increasing the mechanical and pressure integrity of the system.

Introduction
Surface-controlled subsurface safety valves offer improved blowout protection for many wells, and U. S. Geological Survey regulations require the use of surface-controlled valves in many OCS wells. This paper describes the development and testing of one paper describes the development and testing of one type of completion system that Exxon Company, U.S.A., has adopted for the application of surface-controlled valves offshore Louisiana.
Previous Industry Experience Previous Industry Experience Surface-controlled subsurface safety valves have been used in California, Cook Inlet, and overseas with excellent results.' The operation of a typical surface-controlled valve is illustrated in Fig, 1. Hydraulic control pressure inside the valve forces an operating piston downward against a spring. The downward piston downward against a spring. The downward motion of the piston causes the valve mechanism (ball, flapper, or popper) to move to the open position (Fig. 1a). When pressure is released, the spring moves the piston upward, allowing the valve mechanism to close (Fig. 1b). Control has usually been accomplished down a small-diameter hydraulic line installed in the tubing-casing annulus of a conventional completion 2 (Fig. 1c). Valves typically have been set less than 300 ft below the mud line.

Development Requirements
Application of surface-controlled subsurface valves to Exxon's Gulf of Mexico wells required considerable development and adaptation for sand production, paraffin deposition, and tubingless wellbores. production, paraffin deposition, and tubingless wellbores. Although valves are designed to minimize sand erosion and fouling, they still must be tested and occasionally retrieved for maintenance. Therefore, a completion system enabling low-cost valve retrieval and resetting was desirable.In wells subject to paraffin accumulation, valves may have to be set at depths as great as 3,000 ft to be below deposition. To reduce the possibility of mechanical damage when valves are set deep in directional wells and to allow for tubingless completions, it was desirable to eliminate the small hydraulic control line.The above considerations led to the evaluation and development of a completion system that uses the annulus between concentric tubing strings as the hydraulic control channel. This system allows valves to be set deep in the well, provides a high degree of reliability, and is economical to maintain.

Completion System
The new completion system is shown in Fig. 2. A tapered production string is swaged from 3 1/2 to 4 1/2 in. at the desired valve-setting depth. An inner string of 3 1/2 -in. tubing is run inside the 4 1/2 -in. pipe and latched at the taper point. The safety valve is pipe and latched at the taper point. The safety valve is hydraulically controlled by applying pressure to the 3 1/2- x 4 1/2-in. annulus at the surface.
JPT
P. 331