Wellbore Cement Precompression for CO2 Injection Integrity
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Solution Overview
Problem
The issue of cement debonding from the casing in wellbores during carbon dioxide injection, leading to undesirable leaks, is exacerbated by differential contraction due to temperature differences and cement shrinkage, which compromises wellbore integrity and increases operational costs.
Innovation Solution
A method is introduced to design a wellbore with a cement residual compressive stress layer around the casing, involving simulations to determine necessary compressive stresses and fluid heights, ensuring the casing remains in a compressed state to counteract thermal expansion and shrinkage, thereby preventing micro-annulus formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cement is placed in the wellbore annulus to seal the casing, then wellbore integrity is improved, but cement shrinkage and differential contraction cause debonding and micro-annulus formation leading to leakage
Solution Approach 1:
The patent applies preliminary anti-action by pre-compressing the cement slurry to a density higher than both the formation fluid and casing fluid before setting. This pre-compression creates initial compressive stress in the cement that counteracts the subsequent shrinkage and differential contraction forces, preventing debonding and micro-annulus formation before they can occur during normal operation
Solution Approach 2:
The patent changes the density parameter of the cement slurry dynamically - initially placing it at high density to prevent debonding, then allowing it to lighten to match formation fluid density for long-term stability. This parameter transformation resolves the contradiction by using different density states at different time periods to address both immediate sealing and long-term integrity requirements
2Strength
If cement slurry density is increased to prevent debonding, then cement strength and seal quality are improved, but the risk of casing collapse from excessive external pressure increases
Solution Approach 1:
The patent applies preliminary action by temporarily increasing cement slurry density only during the critical setting and early curing period when the cement needs maximum strength development. After the cement achieves sufficient strength, the slurry is allowed to lighten, removing the excessive external pressure while maintaining the strength benefits already gained during the preliminary high-density phase
Solution Approach 2:
The patent makes the cement slurry density dynamic rather than static - it transitions from high density during placement and early setting to lower density after strength development. This dynamic adjustment allows the system to optimize for strength when needed and reduce collapse risk when the cement has already gained sufficient strength
3Ease of manufacture
If minimum cement height is reduced to lower costs, then cementing costs are reduced, but the seal effectiveness and prevention of micro-annulus formation are compromised
Solution Approach 1:
The patent changes the density parameter of the cement slurry to be higher than both the formation fluid and casing fluid, which fundamentally alters the stress distribution in the annulus. This parameter change allows the cement to maintain effective sealing and prevent micro-annulus formation even at reduced heights, because the high density creates sufficient compressive stress to keep the cement bonded to the casing throughout the annulus
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 approach effectively prevents cement debonding and leakage by maintaining wellbore integrity, reducing economic costs associated with remediation and ensuring safe carbon dioxide injection.
Implementation Method 1
cement shrinkage during setting and curing
Implementation Method 2
differential contraction of the casing and cement may lead to creation of a micro-annulus
Implementation Method 3
differential deformations between changing operating environments and cement shrinkage
Implementation Method 4
The annular cement slurry may lose filtrate (slurry minus solid particles that cannot percolate into the formation)
Data Source
AI summary
Embodiments presented provide for a method to negate debonding of the casing from a cement in a wellbore. In one embodiment, the cement around the casing is set with a sufficiently large residual compressive stress, preventing the deboning.