Inner Casing Perforation and Washing for Second Casing Integrity
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Solution Overview
Problem
Existing methods for removing cement from the annulus of an inner casing in a well often damage the surrounding second casing, making it difficult to perforate and wash out the annulus without causing damage.
Innovation Solution
A method and device using a drill pipe string with a perforating gun and cement shattering device to make shallow perforations and disintegrate cement in the annulus, followed by a washing tool to remove the shattered cement, allowing for the inner casing to be cut and pulled without damaging the second casing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If intensive perforation is used to shatter cement and wash out the annulus, then the annulus can be effectively cleaned and the casing can be removed or sealed, but the second casing may be damaged
Solution Approach 1:
The perforation process is divided into two distinct stages: first, shallow perforations are made through the inner casing into the cement annulus; second, the cement is shattered and washed out through these controlled perforations. This segmentation allows effective annulus cleaning while limiting the impact zone to prevent damage to the second casing.
Solution Approach 2:
The perforation charges are designed to create localized effects - shallow perforations that penetrate the inner casing and reach the cement annulus, but do not extend deeply enough to damage the second casing. The shattering and washing operations are then confined to the local annulus region, achieving clean removal without harmful effects on surrounding structures.
2Ease of operation
If the inner casing is cut and pulled out section by section, then the casing can be removed from the well, but the operation becomes time-consuming and complex
Solution Approach 1:
The annulus cement is shattered and washed out in advance, creating a clean annulus space before the casing cutting and pulling operation. This preliminary cleaning action removes the binding agent that would otherwise cause the casing to stick, enabling rapid and easy removal of the inner casing without time-consuming section-by-section extraction.
Solution Approach 2:
The washed-out annulus acts as an intermediary medium that facilitates the separation and removal of the inner casing. By removing the cement binding agent, the annulus becomes a clear pathway that allows the inner casing to be cut and pulled out efficiently, transforming a difficult mechanical extraction into a straightforward operation.
3Reliability
If cement is used to seal the annulus for plugging and abandonment, then the well can be sealed, but the cement must be removed first to allow proper sealing over the required length
Solution Approach 1:
The existing cement annulus is shattered and washed out as a preliminary action before installing new sealing cement. This removes the old cement binding agent that would interfere with the new seal, allowing proper cementing over the required length without having to work around or remove cement during the sealing operation.
Solution Approach 2:
The old annulus cement is extracted and removed through the perforations using the shattering and washing process. This extraction creates a clean annulus space ready for new sealing cement, separating the removal of old material from the installation of new sealing material and simplifying the overall process.
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 method effectively perforates and washes out the annulus cement without harming the second casing, enabling the inner casing to be cut and removed or sealed, while maintaining the integrity of the second casing.
Implementation Method 1
activating explosive charges (11, 21) to disintegrate the cement (102) within the first annulus (C10A)
Implementation Method 2
running a washing tool (3) along the perforated casing portion (C10), washing out the disintegrated cement (102) from the first annulus (C10A)
Data Source
AI summary
A method of sealing a partly or entirely annulus-cemented casing portion of a first casing in a second casing in a petroleum well, includes running a drill pipe string-conveyed perforating gun with a cement shattering device into said well; positioning said perforating gun at said cemented casing portion and activating first, shallow-perforating charges to make first, shallow perforations through said casing portion into thus making a perforated, cement-filled annulus portion and leaving said second casing intact; activating said cement shattering device to disintegrate all or part of said cement within said first perforated annulus portion; running a washing tool along said perforated casing portion, washing out said shattered cement from said perforated annulus portion. The washed-out casing portion may then be cut using a cutter tool and pulled out of hole, or cemented using a cementing tool, or a combination thereof.