On-the-fly Acid Mixing with Retarding Agents
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Solution Overview
Problem
Current acid treatment methods for oil and gas wells face challenges in efficiently stimulating less permeable regions of the reservoir, as high permeability zones tend to dominate acid flow, leading to uneven stimulation and reduced production from other parts of the formation.
Innovation Solution
The development of a method involving the on-the-fly mixing of acid, water, and water-soluble acid retarding agents, along with viscoelastic surfactants, to create a retarded acidizing fluid that can be introduced into the wellbore, allowing for real-time tunable systems and more efficient wellsite operations, thereby redirecting acid flow and enhancing stimulation across the reservoir.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If HCl is injected at low rates into carbonate formations, then wormholes can form to extend radially from the well bore, but the reaction rate is too fast at higher temperatures leading to facial dissolution over wormholing
Solution Approach 1:
Water-soluble retarding agents (such as salts, urea, or amino acids) are introduced as intermediary substances that moderate the reaction between HCl and the carbonate formation. These retarding agents slow down the acid's reactivity, allowing wormhole propagation to continue effectively even at higher temperatures where the acid would otherwise react too quickly and cause facial dissolution.
Solution Approach 2:
The chemical composition parameters of the acid system are modified by adding water-soluble retarding agents. This changes the reaction kinetics of the HCl, reducing its reactivity and enabling controlled wormhole formation across a broader range of injection rates and temperatures.
2Productivity
If HCl is injected at high rates to cause fracturing, then conductive channels can extend the length of the fracture, but the acid unevenly dissolves the walls leading to non-uniform stimulation
Solution Approach 1:
Water-soluble retarding agents act as intermediaries that uniformize the acid's interaction with the fracture walls. By slowing and moderating the reaction rate, these agents prevent localized uneven dissolution and promote more uniform etching of the fracture surfaces, resulting in better conductive channels.
3Productivity
If the highest permeability parts of the formation accept the largest volumes of acid, then these zones have their permeability increased further, but this does little to stimulate production in other parts of the reservoir
Solution Approach 1:
Water-soluble retarding agents serve as mediators that modify acid flow behavior by controlling reaction rates. This allows for more uniform distribution of acid treatment across different permeability zones, enabling stimulation of lower permeability areas that would otherwise be bypassed by preferential flow paths.
4Stability of the object's composition
If organic acids are used to reduce reactivity, then facial dissolution is reduced, but the acids have higher pKa's and will not completely spend in the reservoir
Solution Approach 1:
The system combines HCl (strong acid with low pKa) and water-soluble retarding agents (such as salts, urea, or amino acids) to create a composite acid system. This composite approach maintains the complete spending capability of HCl while using the retarding agents to control reaction rate and reduce facial dissolution, avoiding the incomplete spending problem of organic acids.
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
This approach allows for deeper penetration of the acid into the formation, increasing permeability and productivity by slowing the acid's reaction rate, thereby improving the stimulation of less permeable zones and overall well production.
Implementation Method 1
water-soluble acid retarding agents... to form a retarded acidizing fluid... slowing the acid's reaction rate
Implementation Method 2
A viscoelastic surfactant (VES) from a VES source can also be mixed with the acid, the water and the RA in step a) to form the retarded acidizing fluid
Data Source
AI summary
Described herein are methods for on the fly mixing of retarded acidizing fluids containing acid, a water-soluble acid retarding agent (RA), and optionally a viscoelastic surfactant (VES), and for on the fly mixing of diversion fluids containing VES and RA in the same equipment. Also described are methods of controlling the preparation of such fluids based on feedback composition analyses.