Seawater Acid Stimulation Fluid with Chelating Agent
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Solution Overview
Problem
The use of seawater in acid stimulation of limestone or dolomite formations often results in undesirable solid precipitation due to calcium sulfate formation, which limits the effectiveness of the stimulation process, and existing methods to mitigate this are costly and logistically challenging, especially in offshore operations.
Innovation Solution
A method involving a well servicing fluid composed of a chelating agent, an acid, and an aqueous fluid with sulfate ions, where the chelating agent is added to hinder the reaction of multivalent cations with sulfate ions, reducing precipitate formation, thereby enhancing the stimulation efficiency and reducing logistical complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If seawater is used in acid stimulation instead of fresh water, then logistical challenges and costs are reduced, but calcium sulfate precipitation occurs which reduces stimulation effectiveness
Solution Approach 1:
A chelating agent is introduced as an intermediary substance that binds to calcium ions released during acid dissolution of limestone or dolomite formations. This prevents calcium ions from reacting with sulfate ions in seawater to form precipitates, thereby maintaining stimulation effectiveness while allowing the use of seawater as the acid carrier fluid
Solution Approach 2:
The chemical composition parameters of the acid stimulation fluid are modified by adding chelating agents. This changes the chemical behavior of the system by introducing substances that alter the solubility and reactivity of calcium ions, preventing precipitation and maintaining fluid flow properties throughout the stimulation process
2Object-affected harmful factors
If ion exchange or barium chloride precipitation methods are used to remove sulfate from seawater, then precipitate formation is reduced, but cost and logistical complexity increase significantly
Solution Approach 1:
Instead of removing sulfate ions from seawater through complex ion exchange or precipitation processes, the invention extracts or sequesters the calcium ions that would otherwise react with sulfate to form precipitates. This simpler approach maintains stimulation effectiveness without requiring sophisticated water treatment systems
Solution Approach 2:
The chelating agent is used in relatively small amounts and can be inexpensive, replacing the need for expensive and complex sulfate removal technologies. The chelating agent performs its function during the stimulation process and is then disposed of with the spent acid, eliminating the need for costly water treatment infrastructure
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 method effectively reduces calcium sulfate precipitation, allowing for more efficient well stimulation by maintaining high permeability and reducing the need for pre-treatment of seawater, thus improving the overall stimulation results and operational simplicity.
Implementation Method 1
The concentration of chelating agent is sufficient to hinder a reaction of the increased concentration of multivalent cations with the sulfate ions and to reduce an amount of precipitate produced by the reaction in the well relative to the amount of precipitate that would otherwise have been produced if the chelating agent was not present
Implementation Method 2
The HCl acid is then injected into the formation to dissolve the limestone or dolomite rock, thereby forming a conductive channel extending from the wellbore into the formation area containing the oil and gas
Implementation Method 3
When acid systems are formulated with seawater containing high levels of sulfate ions, calcium sulfate precipitates as the acid reacts with limestone or dolomite formation
Data Source
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AI summary
A well servicing fluid is disclosed. The well servicing fluid is formulated by combining ingredients comprising: an aqueous based fluid comprising sulfate ions at a concentration greater than 50 mg/1; a chelating agent; and an acid in an amount sufficient to result in the well servicing fluid having a pH of 4.5 or less. A method of servicing a well is also disclosed.