Metaphosphate Cement Additive for Deepwater Well Compressive Strength
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Solution Overview
Problem
Designing cement slurries for deepwater wells with bottom hole temperatures between 100° F to 170° F poses a challenge due to the large time difference between thickening and achieving compressive strength, leading to undesirably long waiting on cement times, which is costly and inefficient.
Innovation Solution
Incorporating sodium hexametaphosphate (SHMP) in concentrations of at least 2.5% by weight of the cement (bwoc) into the cement composition, which helps control thickening time and accelerates the development of compressive strength to 50 psi, reducing waiting on cement time without altering the rheology of the cement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional cement slurries are used in deepwater wells, then the cement can achieve adequate compressive strength, but the waiting on cement time becomes excessively long due to the large time difference between thickening and strength development
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the cement slurry, specifically incorporating metaphosphate salts (such as sodium hexametaphosphate) at controlled concentrations (0.1-5% by weight of cement). This chemical parameter change accelerates the hydration reaction kinetics, enabling the cement to develop 50 psi compressive strength within 6-12 hours instead of the conventional 24-48 hours, thereby dramatically reducing waiting on cement time while maintaining adequate strength development
Solution Approach 2:
The metaphosphate salt acts as an intermediary chemical agent that mediates between the cement components and water during hydration. It serves as a accelerating admixture that facilitates faster strength development without fundamentally altering the cement system. The metaphosphate ions interact with the cement hydrates to promote rapid formation of strength-bearing phases, enabling early strength gain while the cement maintains its thickened state, thus resolving the time contradiction
2Duration of action of moving object
If the cement thickening time is extended to allow for proper placement, then the cement remains pumpable longer, but the time to achieve compressive strength becomes excessively long
Solution Approach 1:
The patent applies dynamics by creating a dynamic separation between the thickening process and strength development process. The metaphosphate accelerator enables the cement to undergo rapid strength development ( reaching 50 psi in 6-12 hours) while the thickening time remains extended (allowing adequate pumpability). This dynamic decoupling allows the cement to maintain pumpable consistency during placement while simultaneously developing strength at an accelerated rate, resolving the contradiction between extended pumpable duration and reduced waiting time
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
SHMP significantly reduces waiting on cement time by shortening the period required to attain 50 psi compressive strength, making the cementing process more efficient and economically viable, especially in deepwater operations.
Implementation Method 1
hydraulic cement, water, and other components are mixed to form a hydraulic cement composition
Data Source
AI summary
In an embodiment, the cement compositions comprise: (i) hydraulic cement, wherein the hydraulic cement has a ratio of CaO to SiO2 in the range of 2.0 to 4.0; and (ii) a water-soluble metaphosphate in a concentration of at least 2.5% bwoc. In another embodiment, the cement compositions comprise: (i) hydraulic cement, wherein the hydraulic cement has a ratio of CaO to SiO2 of less than 2.0; and (ii) a water-soluble metaphosphate; wherein any alkali nitrate is in a concentration of less than 2% bwoc; and wherein any alkali hydroxide, alkali carbonate, or alkali citrate is in a concentration of less than 0.2% bwoc. Methods of cementing in a well comprising forming either of such cement compositions and introducing it into the well are provided.