THPS and Chelating Agent Scale Removal in Wellbores
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Solution Overview
Problem
Current methods for removing iron sulfide and calcium carbonate scale deposits from wellbores and equipment are inefficient, often requiring strong acids that are corrosive and hazardous, or labor-intensive mechanical scrubbing, and fail to address the presence of mixed scale types, particularly pyrite and marcasite forms, and calcium carbonate scales simultaneously.
Innovation Solution
A composition comprising tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in the range of 10 wt. % to 40 wt. % combined with chelating agents like HEDTA, and optionally converting agents, applied at a pH of 6.0 to 8.0 and heated to 70 to 180°C, is injected into wells to dissolve and remove heterogeneous iron sulfide and calcium carbonate scales without the need for corrosion inhibitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If strong acid (10-20 wt% HCl) is used to dissolve iron sulfide and calcium carbonate scales, then the scale removal effectiveness is improved, but the corrosion damage to wellbore equipment and formation increases, and toxic H2S gas is generated
Solution Approach 1:
The patent changes the chemical parameters by using THPS at controlled concentrations (10-40 wt%) with chelating agents at specific pH ranges (6.0-8.0), replacing the traditional strong acid system. This parameter change achieves effective scale removal while avoiding the harmful effects of high acidity and H2S generation.
Solution Approach 2:
The patent employs a composite chemical formulation combining THPS with chelating agents (such as EDTA, DTPA, or HEDTA) and optionally converting agents. This composite approach synergistically enhances scale removal effectiveness while maintaining safety by preventing corrosion and avoiding toxic gas production.
2Productivity
If mechanical scrubbing methods (milling, high pressure water jetting) are used to remove scale deposits, then the scale removal capability is improved, but the labor intensity and time consumption increase significantly
Solution Approach 1:
The patent replaces mechanical scrubbing methods with a chemical dissolution system based on THPS and chelating agents. This substitution eliminates the need for manual intervention, high-pressure equipment, and extensive labor, allowing the scale to be removed chemically through injection and contact time.
Solution Approach 2:
The chemical formulation automatically dissolves and removes scale deposits when injected into the wellbore, requiring no external mechanical energy input or manual operation. The system performs the removal function autonomously through the chemical reaction between the formulation and the scale deposits.
3Object-affected harmful factors
If oxidizing agents are used to remove iron sulfide scales, then the toxicity hazards are avoided, but the oxidation products including elemental sulfur are produced which are corrosive to pipes and equipment
Solution Approach 1:
The patent changes the chemical mechanism from oxidation to chelation and dissolution. By using THPS with chelating agents at controlled pH levels, the system removes iron sulfide scales without generating corrosive oxidation products like elemental sulfur, while also avoiding toxicity hazards.
4Productivity
If Acrolein is used for treating scale, then the scale removal effectiveness is improved, but health, safety, and environmental issues arise
Solution Approach 1:
The patent replaces Acrolein with THPS combined with chelating agents, changing the chemical parameters to achieve scale removal through a safer mechanism. This substitution maintains effectiveness while eliminating the severe health, safety, and environmental hazards associated with Acrolein.
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 solution effectively removes at least 50% of iron sulfide and calcium carbonate scales, increasing well permeability and preventing scale formation, while being non-corrosive and safer than traditional methods, with the THPS/HEDTA formulation preventing calcium sulfate precipitation and enhancing core permeability.
Implementation Method 1
A composition comprising tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in the range of 10 wt. % to 40 wt. % combined with chelating agents like HEDTA... is injected into wells to dissolve and remove heterogeneous iron sulfide and calcium carbonate scales
Implementation Method 2
The composition... is injected into wells to dissolve and remove heterogeneous iron sulfide and calcium carbonate scales
Implementation Method 3
applied at a pH of 6.0 to 8.0 and heated to 70 to 180°C
Data Source
AI summary
A method of removing a heterogeneous scale from a surface in fluid communication with a wellbore and/or subterranean formation comprising contacting the scale with a composition comprising tetrakis(hydroxmethyl)phosphonium sulfate (THPS) and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (THEDTA) to dissolve the scale having a pH in the range of about 6.0 to 8.0. The composition is suitable to remove iron sulfide and calcium carbonate scale in the absence of corrosion resistance at a temperature up to about 150° C. Also, the composition may be used remove scale from surface pipe line and other petroleum oil handling equipment.