Low CTE Cement Slurry and Casing for Thermal Stress Reduction
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Solution Overview
Problem
Cement sheaths in subterranean wells, particularly in steam-injection wells, face challenges due to large temperature fluctuations, leading to thermal stress and loss of zonal isolation, as conventional cements with high thermal expansion coefficients (CTEs) can cause microannulus formation and deterioration.
Innovation Solution
Incorporating fillers with low or negative thermal expansion coefficients, such as INVAR™ alloy and zirconium tungstate, into the cement slurry or using casing strings with low CTE metals like INVAR™, KOVAR™, and OSPREY™ alloys to reduce thermal contraction and expansion stresses, thereby maintaining zonal isolation during temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cement with high thermal expansion coefficient is used, then the cement can be easily manufactured and applied, but thermal stress builds up during temperature fluctuations causing loss of zonal isolation
Solution Approach 1:
The patent changes the thermal expansion parameter of the cement by incorporating fillers with low or negative thermal expansion coefficients (such as microsilica, metakaolin, and zirconium tungstate). This modifies the physical-chemical properties of the cement composite to reduce thermal stress during temperature fluctuations, thereby maintaining zonal isolation reliability in thermal recovery wells.
Solution Approach 2:
The patent creates a composite cement material by combining conventional cement with specific fillers that have low or negative thermal expansion coefficients. This composite structure allows the cement to resist thermal stress while maintaining its cementing function, solving the contradiction between ease of manufacture and thermal stress resistance.
2Strength
If expanding cements are used to maintain cement/casing bonding, then bonding is improved, but in weak formations expansion causes cement sheath to move away from casing creating microannulus
Solution Approach 1:
The patent changes the expansion parameter of the cement by incorporating fillers with low or negative thermal expansion coefficients, creating a cement that does not expand significantly during setting. This prevents the cement sheath from moving away from the casing in weak formations while still achieving adequate bonding strength through the chemical adhesion of the cement matrix.
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 use of low- or negative-CTE materials in cement compositions and casing strings significantly reduces thermal contraction and expansion-induced stresses, minimizing microannulus formation and maintaining zonal isolation, even under extreme temperature variations.
Implementation Method 1
Incorporating fillers with low or negative thermal expansion coefficients, such as INVAR™ alloy and zirconium tungstate, into the cement slurry to reduce thermal contraction and expansion stresses
Implementation Method 2
using casing strings with low CTE metals like INVAR™, KOVAR™, and OSPREY™ alloys to reduce thermal contraction and expansion stresses
Data Source
AI summary
Methods for cementing a subterranean well comprise installing a casing string into a borehole, wherein the casing string comprises a metal having a coefficient of thermal expansion (CTE) lower than about 6×10−6/° C. A cement sheath is then placed between the exterior surface of the casing string and the formation wall. The low-CTE metal may reduce casing shrinkage when the well temperature falls during stimulation treatments, cyclic steam injection or when the well temperature reaches equilibrium at the top of a long casing string.