Mechanical Hold-Down Assembly for Well Tie-Back Strings

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Solution Overview

Problem

Existing subsea well tie-back systems face challenges with load-bearing capacity and leakage risks, particularly when using cement or hydraulic cylinders above the primary seal in hold-down mechanisms.

Innovation Solution

A mechanical hold-down assembly for a well tie-back string that includes bi-directional slips, an annular seal assembly, latch rings, and shear bolts, allowing for secure anchoring and tensioning of the tie-back string without relying solely on cement or hydraulic cylinders above the primary seal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If cement is used to anchor the hold-down mechanism, then the anchoring function is provided, but the load-bearing capacity is insufficient

Engineering Contradiction:

Improveload-bearing capacityVSAvoidanchoring reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The hold-down mechanism is divided into multiple independent hold-down cones (first hold-down cone, second hold-down cone, third hold-down cone) that can be sequentially activated. Each cone provides a portion of the total holding force, distributing the load and enabling the system to achieve high load-bearing capacity that exceeds what a single cement anchor could provide.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Hydraulic cylinders are used to actuate the hold-down cones, providing controlled mechanical force to press the cones against the wellhead. This hydraulic actuation system enables reliable and adjustable application of large forces to achieve secure anchoring with sufficient load-bearing capacity.

Inventive Principle:

Principle #29Pneumatics and hydraulics

2Ease of operation

If hydraulic cylinders are placed above the primary seal, then the hold-down mechanism can be actuated, but leakage risk increases

Engineering Contradiction:

Improvehold-down actuationVSAvoidleakage risk

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The hold-down function is segmented into multiple cones actuated by separate hydraulic cylinders. This segmentation allows the system to achieve reliable actuation through distributed hydraulic forces while maintaining sealing integrity, as each cylinder-cone assembly can be independently controlled and sealed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The hold-down cones are positioned and sealed against the wellhead before full actuation occurs. The sealing elements are pre-positioned to create barriers that prevent leakage paths, allowing the hydraulic cylinders to actuate the mechanism without creating leakage risks.

Inventive Principle:

Principle #10Preliminary action

3Strength

If multiple hold-down cones are used, then load-bearing capacity increases, but device complexity increases

Engineering Contradiction:

Improveload-bearing capacityVSAvoidmechanism complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

Multiple hold-down cones share the same design and function, each capable of providing identical holding force. This universality allows the system to increase load-bearing capacity by simply adding more identical units rather than designing increasingly complex single-unit solutions. The repeated modular units simplify the overall design approach.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The hold-down mechanism transitions from a static cement anchor to a dynamic, sequentially actuated system. The hydraulic cylinders can activate cones in sequence, allowing the system to adapt its holding force dynamically. This dynamic activation pattern simplifies control compared to designing a single overly-complex high-strength anchor.

Inventive Principle:

Principle #15Dynamics

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

The mechanical hold-down assembly provides enhanced load-bearing capacity and reduces leakage risks by securely anchoring the tie-back string, maintaining tension, and creating a reliable fluid flow path, thereby improving the efficiency and reliability of subsea operations.

Implementation Method 1

bi-directional slips... securely anchoring the tie-back string

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 2

bi-directional slips... securely anchoring the tie-back string

Methodology Applied

Scientific EffectMechanical interlocking: Mechanical Fastener

Implementation Method 3

shear bolts... maintaining tension of the tie-back string

Methodology Applied

Scientific EffectShear stress: Shear Stress

Implementation Method 4

annular seal assembly... creating a reliable fluid flow path

Methodology Applied

Scientific EffectSealing:

Data Source

PatentUS9982504B2Mechanical hold-down assembly for a well tie-back string

Publication Date: 2018.05.29 INNOVEX INTERNATIONAL INC

AI summary

An improved hold-down assembly for a well tie-back string and methods of use of the same are disclosed. The improved hold-down assembly includes a tie-back string and a hold-down assembly coupled to the tie-back string. The hold-down assembly includes one or more slips and a packer assembly disposed about the tie-back string.