Refracturing Borehole Isolators for Thermal Shift Alignment

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Solution Overview

Problem

Existing methods for re-fracturing boreholes face uncertainties in sealing off initial perforations, leading to inefficiencies and high costs, with issues such as incomplete sealing, misalignment due to thermal shifts, and high operational costs.

Innovation Solution

A bottom hole assembly with isolators positioned offset from existing perforations, allowing new perforations to be made through the isolators, which are designed to maintain alignment despite thermal shifts, and optionally featuring an anchor to prevent axial movement, ensuring effective isolation and flow rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If chemicals are used to seal existing perforations, then the perforations can be closed off, but the distribution of material is uncertain and some perforations may remain open

Engineering Contradiction:

Improvesealing effectivenessVSAvoiduncertainty of material distribution

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

A packer is introduced as an intermediary mechanical device to seal the annulus between the tubing and borehole wall. This packer provides a reliable physical barrier that prevents chemicals from leaking into existing perforations, ensuring complete isolation without the distribution uncertainties associated with chemical injection alone.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If sliding sleeves are used to close existing perforations, then perforations can be sealed, but the cost is high and there is uncertainty whether sleeves will shift to closed position

Engineering Contradiction:

Improveperforation closureVSAvoidsleeve shifting mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The complex sleeve shifting mechanism is removed entirely from the system. Instead, a simpler packer design is used that seals the annulus mechanically without requiring movable parts or complex shifting operations. This eliminates both the high cost and reliability concerns associated with sleeve-based systems.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The packer is designed as a simple, cost-effective component that performs its sealing function reliably without requiring expensive mechanisms. The packer remains in place to provide continuous sealing, eliminating the need for repeated operational trips.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If sleeves are placed over existing perforations, then perforations may be covered, but the placement location uncertainty and sealing effectiveness are concerns

Engineering Contradiction:

Improveperforation coverageVSAvoidplacement location accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The packer serves as an intermediary sealing element that is positioned in the annulus between the tubing and borehole wall, upstream of the existing perforations. This location provides a reliable sealing point that is independent of the exact perforation locations, ensuring complete isolation without requiring precise placement over each perforation.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Productivity

If new perforations are made without isolating existing ones, then re-fracturing can proceed, but sand or water from existing fractures may be produced

Engineering Contradiction:

Improvere-fracturing efficiencyVSAvoidsand and water production

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The borehole is segmented into isolated zones using the packer as a barrier. The packer divides the annulus into an upper sealed zone containing existing perforations and a lower active zone where new perforations are created. This segmentation prevents harmful materials from existing fractures from mixing with production from new fractures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The packer acts as an intermediary barrier that physically separates the existing and new fracture zones. This mechanical separator ensures that fluids and solids from existing perforations cannot contaminate production from newly created perforations, enabling clean re-fracturing operations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9719339B2Refracturing an already fractured borehole

Publication Date: 2017.08.01 BAKER HUGHES CO

AI summary

A well with existing perforations is re-fractured by positioning isolators at locations offset from the existing perforations and perforating through those isolators. The isolators are part of a bottom hole assembly that can be delivered on coiled or rigid tubing. The initial fractures can be straddled by the isolators with no mandrel openings between them to effectively isolate the existing perforations as new perforations take place through the isolators. The elements of the isolators can have internal gaps to allow for axial shifting after perforation that is thermally induced. The gaps assure remaining alignment with the new perforations despite some axial shifting. The bottom hole assembly can alternatively have an anchor to resist thermally induced forces that can cause axial shifting.