Resilient Wellbore Cement Composition for Gas-Tight Stress Cycling
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Solution Overview
Problem
Wellbore cement sheaths fail due to pressure- or temperature-induced stresses during well operations, creating paths for formation fluids to enter the annulus and compromising well safety and economic life.
Innovation Solution
A cement composition comprising a base cement, silica flour, and a cross-linked polyrotaxane additive, with the polyrotaxane present in a range of 0.05% to 5% by weight of cement, is used to form a cement slurry that is cured within the wellbore, providing improved resiliency and resistance to stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cement compositions are used to cement the wellbore, then the cement sheath provides initial support and zonal isolation, but the cement sheath fails under pressure- or temperature-induced stresses during well operations
Solution Approach 1:
The patent applies composite materials by combining conventional cement with polyrotaxane polymer additives to create a cement-polymer composite system. The polyrotaxane forms a three-dimensional cross-linked network within the cement matrix, creating a composite material that maintains the cement's binding properties while adding elastic resilience and stress absorption capabilities, thereby preventing cement sheath failure under operational stress cycles
Solution Approach 2:
The patent applies parameter changes by modifying the mechanical properties of cement through the addition of polyrotaxane, which changes the Young's modulus and stress-strain characteristics. The polyrotaxane additive alters the cement's physical parameters to provide both strength and elasticity, enabling the cement sheath to withstand repeated stress cycles without failure while maintaining gas-tight integrity
2Reliability
If the cement sheath is designed to withstand high stresses, then well safety is improved, but the complexity of the cement composition increases
Solution Approach 1:
The patent applies the intermediary principle by using polyrotaxane polymer as a mediating substance between the cement matrix and the applied stresses. The polyrotaxane acts as a stress-absorbing intermediary that protects the cement structure from direct stress exposure, allowing the cement composition to remain relatively simple while still achieving high stress resistance and well safety
3Reliability
If the cement slurry is pumped to the wellbore and cured, then a cement structure is formed to provide zonal isolation, but stress cycles during well operations cause failure creating paths for formation fluids
Solution Approach 1:
The patent applies beforehand cushioning by incorporating polyrotaxane into the cement composition before the cement is pumped and cured in the wellbore. The polyrotaxane creates a pre-formed elastic network that cushions the cement structure against future stress cycles, preventing crack initiation and propagation before they can occur during well operations, thereby maintaining zonal isolation integrity
Data Source
AI summary
Cement slurries including a cement composition having a base cement, silica flour, and a cross-linked polyrotaxane additive, water, and latex. The cement composition includes the cross-linked polyrotaxane additive in an amount in a range of 0.05% to 5% by weight of cement (BWOC). Cement structures formed by curing a cement slurry within a wellbore and the cement structure is located within the wellbore. Methods for cementing a wellbore, including forming a cement slurry by mixing a cement composition, water, and latex, pumping the cement slurry to a selected location within the wellbore, and curing the cement slurry at the selected location to form a cement structure.