Riser recoil preventer system

• US 4,351,261 A
• Filed: 05/01/1978
• Issued: 09/28/1982
• Est. Priority Date: 05/01/1978
• Status: Expired due to Term

• Current Assignee: Sedco Incorporated
• Original Assignee: Sedco Incorporated
• Inventors: Shanks, Forrest E.
• Primary Examiner(s): Blix, Trygve M.
• Assistant Examiner(s): Sotelo, Jesus D.
• Application Number:
  US05/901,520
• Time in Patent Office: 1,611 Days
• Field of Search: 114/213, 114/256, 114/264, 114/265, 175/5, 175/7, 175/8, 175/27, 254/93 R, 254/172, 254/173 B, 92/10, 166/355, 91/4
• US Class Current: 114/264
• CPC Class Codes: B63B 1/107 Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
• CPC Class Codes: B63B 2001/128 comprising underwater connectors between the hulls
• CPC Class Codes: B63B 2035/448 Floating hydrocarbon production vessels, e.g. Floating Production Storage and Offloading vessels [FPSO]
• CPC Class Codes: B63B 35/44 Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices construction methods for floating offshore platforms B63B75/00
• CPC Class Codes: B66C 13/02 Devices for facilitating retrieval of floating objects, e.g. for recovering crafts from water handling live-boats B63B; salvaging, or hauling-out on slipways, waterborne vessels B63C; winding mechanism controls B66D1/52
• CPC Class Codes: E21B 19/006 including heave compensators
• CPC Class Codes: E21B 19/09 specially adapted for drilling underwater formations from a floating support using heave compensators supporting the drill string
• CPC Class Codes: E21B 7/128 from floating support with independent underwater anchored guide base

Abstract

A recoil system and method for supporting a marine riser which is extended from offshore well head equipment to a floating platform are disclosed. The purpose of the recoil system is to prevent a violent collisin of the riser with the platform when the riser becomes separated from the well head equipment during a planned or an emergency disconnect operation. Upon disconnection of the riser from the well head equipment, the lifting force applied to the riser is reduced to a predetermined lower level and the riser is retracted to an elevated position above the well head equipment to permit unobstructed excursions of the riser. A variable lifting force is applied to the riser to maintain the riser substantially in equilibrium in the retracted position as the floating platform heaves relative to the riser in response to wave action. The riser is supported by a tensioner assembly which includes a hydraulic cylinder having a housing member attached to the platform, a movable piston dividing the housing member into a high pressure hydraulic chamber and a low pressure hydraulic chamber, and a rod connected to the piston and coupled to the riser for applying a lifting force to the riser in response to pressurization of the hydraulic pressure chamber. Collision of the riser against the floating platform is prevented by apparatus which includes a reservoir of compressed gas and a valve connected intermediate the compressed gas reservoir and the low pressure hydraulic chamber for selectively applying a pneumatic or pneumatic over hydraulic pressure load to the piston in opposition to the hydraulic pressure load when the riser is disconnected from the well head equipment.

Claims

1. Apparatus for applying tension to a marine riser during a tensioning mode of operation and for relieving the tension during a disconnect mode of operation comprising, in combination:

cylinder means having a housing and a movable piston dividing the housing into a low pressure and a high pressure hydraulic chamber;

a rod connected to the piston for driving a load in response to pressurization of the high pressure chamber;

traveling sheave means mounted on the piston rod;

a power transmission cable disposed in reeved engagement with the traveling sheave means for applying a lifting force on the riser;

a first hydraulic accumulator connected in fluid communication with the high pressure chamber for supplying hydraulic fluid to and for receiving hydraulic fluid from the high pressure chamber in response to changes in its volume;

a second hydraulic accumulator connected in fluid communication with the low pressure chamber for supplying hydraulic fluid to and for receiving hydraulic fluid from the low pressure chamber in response to changes in its volume;

a first reservoir of compressed gas connected in fluid communication with the first hydraulic accumulator for pressurizing the hydraulic fluid in the first accumulator;

a second reservoir of compressed gas having an inlet port connected in fluid communication with the first reservoir and having an outlet port connected in fluid communication with the low pressure chamber for applying a pneumatic pressure load on the piston in combination with the low pressure hydraulic load in opposition to the high pressure hydraulic load;

first valve means connected intermediate the first reservoir and the first hydraulic accumulator for admitting compressed gas into the first accumulator during the tensioning mode of operation and for sealing the first accumulator during the disconnect mode of operation; and

,

second valve means connected intermediate the second reservoir and low pressure chamber for sealing the outlet port of the second reservoir during the tensioning mode of operation and for admitting compressed gas into the low pressure chamber during the disconnect mode of operation.

2. The riser tensioner apparatus as defined in claim 1, the combination further including a regulator connected intermediate the first reservoir and the second reservoir for maintaining the pressure of the second reservoir at a predetermined lower level relative to the pressure of the first reservoir.

3. In combination:

an offshore production facility including a floating platform stationed above an ocean floor production site in which well head equipment is embedded;

a marine riser connected to the well head equipment and extending from the production site to the floating platform;

a telescoping joint coupling the riser to the floating platform;

a tensioner assembly coupled intermediate the platform and marine riser for applying a tension load on the riser, the tensioner assembly including a hydraulic cylinder having a housing member attached to the platform, a movable piston dividing the housing member onto a high pressure hydraulic chamber and a low pressure hydraulic chamber, a rod connected to the piston and coupled to the riser for applying a tension load to the riser in response to pressurization of the high pressure chamber; and

,

a riser recoil preventer assembly including a reservoir of compressed gas and valve means connected intermediate the compressed gas reservoir and low pressure chamber for selectively opening a pneumatic circuit between the reservoir and low pressure chamber for applying a pneumatic over hydraulic pressure load on the piston in opposition to the high pressure hydraulic load, thereby relieving the tension load on the riser and limiting the displacement of the telescoping joint to prevent its collision with the platform in response to disconnection of the marine riser from the well head equipment.

4. In a tensioner assembly for applying a tension load to a marine riser connected to well head equipment and extending to a floating platform in an offshore production site, the tensioner assembly being of the type including a hydraulic cylinder having a housing, a piston dividing the housing into a high pressure hydraulic chamber and a low pressure hydraulic chamber, and a rod attached to the piston for applying a tension load to the marine riser, the combination with the hydraulic cylinder of a reservoir of compressed gas and valve means connected intermediate the reservoir and low pressure chamber for selectively applying a pneumatic over hydraulic load to the piston in opposition to the hydraulic load when the riser is disconnected from the well head equipment.

5. In a tensioner assembly for applying a tension load to a marine riser connected to well head equipment and extending to a floating platform in an offshore production site, the tensioner assembly being of the type including a hydraulic cylinder having a housing, a piston coupled to the housing defining a pressure chamber that changes in volume with movement of the piston relative to the housing, a rod attached to the piston for applying a tension load to the marine riser in response to pressurization of the pressure chamber, a first hydraulic accumulator connected in fluid communication with the pressure chamber for maintaining hydraulic fluid in the pressure chamber under pressure, and a first reservoir of compressed gas connected in fluid communication with the first hydraulic accumulator for maintaining a pressure load on the hydraulic fluid, the combination with the hydraulic cylinder of a second hydraulic accumulator connected in fluid communication with the pressure chamber, a second reservoir of compressed gas connected in fluid communication with the second accumulator, a first valve connected intermediate the first hydraulic accumulator and pressure chamber for selectively opening and closing a fluid circuit from the first hydraulic accumulator to the pressure chamber, and a second valve connected intermediate the second hydraulic accumulator and pressure chamber for selectively opening or closing a fluid circuit from the second hydraulic accumulator to the pressure chamber, a first volume of compressed gas disposed in the first reservoir and accumulator at a pressure level sufficient to maintain tension loading on the marine riser while it is attached to the well head equipment, and a second volume of compressed gas disposed in the second reservoir and second hydraulic accumulator at a pressure level less than the pressure level of the first reservoir but which is sufficient to retract the riser upon disconnection of the riser from the well head equipment and maintain the suspended riser substantially in equilibrium at the retracted position as the platform heaves and falls in response to wave movements.