Offshore Drilling Vessel Heave Compensation via Mobile Working Deck
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Solution Overview
Problem
Existing offshore drilling vessels with RamRig installations face challenges in effectively compensating for heave motion, which can lead to undue vertical motion and pressure variations in subsea wellbores during drilling operations.
Innovation Solution
The implementation of a vertically mobile working deck suspended from independent cables and an integrated heave compensation system that synchronizes the motion of the working deck and the travelling top drive carrier, using a common heave compensation device to maintain consistent load on the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stationary drill floor with slip device is used, then the structure is simple and stable, but heave compensation is insufficient leading to vertical motion and pressure variations in the wellbore
Solution Approach 1:
The drilling installation is segmented into a stationary drill floor and a mobile working deck. The mobile working deck can be vertically positioned independently and equipped with its own slip device, allowing heave compensation to be applied specifically where needed without redesigning the entire drill floor structure.
Solution Approach 2:
The working deck is made dynamically positionable vertically relative to the stationary drill floor through cable suspension and winch mechanisms. This dynamic positioning capability enables the working deck to compensate for heave motion while the main drill floor remains stationary and structurally simple.
2Reliability
If independent cable suspension for working deck is implemented, then heave compensation is improved, but the system complexity increases
Solution Approach 1:
The winch system serves multiple functions: it suspends the working deck vertically, provides heave compensation through synchronized operation with the drill string, and enables positional adjustment of the working deck. This multi-functionality reduces the need for separate mechanisms for each function.
Solution Approach 2:
The independent cable suspension system acts as an intermediary between the stationary drill floor and the mobile working deck, allowing the working deck to move independently for heave compensation while maintaining connection to the overall drilling system through the cables and winches.
3Object-affected harmful factors
If synchronous heave compensation is applied to both drill string and working deck, then vertical motion in wellbore is reduced, but control system complexity increases
Solution Approach 1:
The integrated heave compensation system uses feedback from heave sensors and position sensors to continuously monitor the motion of the vessel and adjust the positioning of both the drill string and working deck. This closed-loop control ensures synchronous compensation and minimizes vertical motion in the wellbore.
Solution Approach 2:
The heave compensation controls for the drill string and working deck are merged into a single integrated system. This allows both components to be compensated synchronously based on the same heave data, reducing the need for separate control systems and simplifying the overall control architecture.
4Adaptability or versatility
If mobile working deck with slip device is used, then operational flexibility is improved, but load transfer complexity increases
Solution Approach 1:
The working deck slip device is designed to automatically engage and disengage from the drill string during operations. This self-service capability allows for quick load transfer between the drill string and working deck without requiring complex manual intervention or additional positioning mechanisms.
Solution Approach 2:
The working deck is positioned at the same vertical level as the drill floor during normal operations, creating an equipotential condition that facilitates easy load transfer. This level alignment eliminates the need for complex lifting or lowering mechanisms during routine load transfers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables full heave compensation during operations like tripping in or out of drill strings, reducing vertical motion and pressure variations in the wellbore, thereby enhancing operational efficiency and safety.
Implementation Method 1
vertically oriented hydraulic piston-and-cylinder type lift devices, each having one of the cylinder and the piston rod thereof fixed in relation to the hull and the other one of the cylinder and the piston rod supporting the top sheave assembly thereon
Implementation Method 2
The hydraulic circuit includes a pressurized gas buffer connected via a piston accumulator to the hydraulic circuit. Passive heave compensation is done on the basis of the pressurized gas buffer as is known in the art. Effectively the piston rods of the lift devices rest on a gas spring.
Implementation Method 3
Active heave compensation is obtained by control of the hydraulic pumps on the basis of a heave sensor
Implementation Method 4
a set of hydraulic pumps in the hydraulic circuit to provide a desired hydraulic liquid flow to the lift devices
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
An offshore drilling vessel comprises a floating hull, a moonpool, and a drilling tower. A main hoisting device comprises a travelling top drive carrier, a top sheave assembly with carrier suspension cable sheaves, and vertically oriented hydraulic piston-and-cylinder type lift devices. Carrier suspension cables have one end secured to the carrier and extend over a respective sheave to another end connected to one of an anchor or to a winch fixed in relation to the hull. A vertically mobile working deck is provided with a slip device that is configured to suspend a tubulars string in the firing line. The working deck is suspended from a working deck suspension cable which is reeved independent from the lift devices. An integrated heave compensation system is provided that is configured to establish, in operation thereof, a heave compensated motion of the working deck and a synchronous heave compensated motion of the carrier in order to obtain synchronous heave compensated motions of the working deck and the carrier. The system comprises a common heave compensation device that acts on both the carrier suspension cables and the working deck suspension cables so that when a load formed by a tubulars string initially suspended from the carrier is transferred to the slip device or vice versa, the load on the common heave compensation device remains substantially the same.