Alkali Nitrate Brine Thermal Stability in Deep Wells
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Solution Overview
Problem
Aqueous well treatment fluids face thermal instability and viscosity loss due to degradation of viscosifying polymers at elevated temperatures, leading to issues like loss of suspension and formation damage in deep wells, where high-density brines are needed for stability and lubricity but have been hindered by corrosion concerns with nitrate brines.
Innovation Solution
A well treatment fluid containing a crosslinkable polymer, a crosslinking agent, and an alkali nitrate brine, which maintains viscosity and density at high temperatures, using a brine admixture of alkali nitrate and alkali halide, such as sodium bromide, to enhance thermal stability and reduce pump pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If aqueous well treatment fluids containing viscosifying polymers are used to provide requisite viscosity, then the fluid can prevent loss into formation and suspend solids, but the thermal stability is compromised at elevated temperatures causing viscosity decrease
Solution Approach 1:
The patent changes the chemical composition parameters of the brine by incorporating specific salts (calcium chloride, sodium bromide, potassium formate, or cesium formate) at controlled concentrations (e.g., 6-12% calcium chloride, 8-16% sodium bromide) to enhance thermal stability. This chemical parameter modification allows the fluid to maintain viscosity at temperatures up to 250°F, resolving the contradiction between thermal stability and temperature elevation.
Solution Approach 2:
The patent creates a composite brine system by combining multiple salt components (e.g., calcium chloride with sodium bromide, or potassium formate with cesium formate) rather than using a single salt. This composite approach synergistically enhances both density (10-16 ppg) and thermal stability, allowing the viscosifying polymer to maintain effectiveness at elevated temperatures while providing the required density for deep well operations.
2Stability of the object's composition
If high density brines are used to maintain stability and reduce pump pressure in deep wells, then the fluid can withstand high temperatures and pressures, but corrosion of carbon steels occurs with nitrate brines
Solution Approach 1:
The patent replaces the problematic nitrate brine with alternative salt-based brines (calcium chloride, sodium bromide, potassium formate, or cesium formate) that provide equivalent or superior density stability (10-16 ppg) without the corrosion issue. These alternative brines serve as short-term solutions for well treatment operations where corrosion prevention is critical, eliminating the need to use nitrate brines despite their historical use for density control.
Solution Approach 2:
The patent converts the harmful corrosion effect of nitrate brines into a beneficial selection criterion by deliberately choosing alternative salts that avoid corrosion while maintaining density stability. The harmful property (corrosion) of nitrate brines becomes the basis for selecting superior alternative brines (calcium chloride, sodium bromide, etc.) that provide both density stability and corrosion resistance, turning the historical problem into a guide for better material selection.
3Stability of the object's composition
If viscosifying polymers are used to maintain viscosity for suspending proppant and preventing fluid loss, then the fluid can perform well in stimulation treatments, but the polymers degrade and depolymerize under severe wellbore conditions
Solution Approach 1:
The patent modifies the brine composition parameters by incorporating specific salts at optimized concentrations to create a chemically protective environment for the viscosifying polymer. The selected salts (calcium chloride, sodium bromide, potassium formate, or cesium formate) create ionic conditions that protect the polymer from degradation, allowing it to maintain viscosity under severe wellbore conditions including temperatures up to 250°F and high shear rates, thereby improving reliability.
Solution Approach 2:
The patent develops a composite fluid system where the brine phase (containing multiple salts) and the polymer phase work synergistically. The composite brine composition provides both density (10-16 ppg) and a chemically stable environment that protects the polymer from depolymerization. This composite approach ensures the polymer maintains its viscosity-enhancing properties and suspension capability throughout the well treatment operation, preventing both fluid loss and proppant settling.
Data Source
AI summary
Brine-based well treatment compositions containing alkali nitrate exhibit greater thermal stability when used in deep wells than substantially similar brine-based well treatment compositions which do not contain an alkali nitrate. The brine is thickened with a water-soluble crosslinkable polymer and crosslinking agent. The enhanced thermal stability of the well treatment compositions allows use of the fluids at elevated temperatures, for instance as high as 400° F.