Ionic Polymer Gel Crosslinking in Low-Conductivity Well Fluids
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Solution Overview
Problem
Existing well treatment methods face challenges in crosslinking anionically or cationically charged polymers in low-conductivity fluid media without adversely impacting gel strength and thermal persistence, particularly when using borate or metal crosslinkers.
Innovation Solution
The use of surfactants with oppositely charged moieties is introduced to facilitate early borate crosslinking in a low-conductivity aqueous medium, followed by metal crosslinking at higher temperatures, allowing for reversible and persistent gel formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If borate crosslinking is used in low-conductivity media, then early gel formation is achieved, but gel strength and thermal persistence are adversely impacted
Solution Approach 1:
The patent introduces oppositely charged surfactants as intermediary agents that facilitate borate crosslinking in low-conductivity media by neutralizing charge repulsion between polymer chains. The surfactant acts as a mediator that enables the borate crosslinking reaction to proceed effectively without requiring high ionic strength, thus allowing early gel formation while preserving gel strength and thermal persistence.
Solution Approach 2:
The patent changes the chemical environment by adjusting pH levels and introducing surfactants to modify the crosslinking mechanism. By controlling pH and surfactant concentration, the system enables borate crosslinking to occur effectively in low-conductivity media, achieving both timely gel formation and maintained gel strength through optimized reaction conditions.
2Reliability
If metal crosslinking is delayed to avoid high shear sensitivity, then fluid viscosity is maintained during pumping, but crosslinking efficiency decreases
Solution Approach 1:
The patent segments the crosslinking process into two distinct stages: first, borate crosslinking occurs early to provide reversible, shear-sensitive gelation that maintains viscosity during pumping; second, metal crosslinking occurs later to provide irreversible, persistent gelation for long-term gel strength. This segmentation allows each crosslinking mechanism to perform its optimal function at the appropriate time.
Solution Approach 2:
The patent applies preliminary borate crosslinking before metal crosslinking to establish initial gel structure and viscosity. This preliminary action creates a gel network that can withstand pumping shear stresses, while the subsequent metal crosslinking reinforces the structure for long-term stability, thereby maintaining both viscosity stability and crosslinking efficiency.
3Productivity
If high pH is used to promote borate crosslinking, then crosslinking rate increases, but polymer stability and gel quality deteriorate
Solution Approach 1:
The patent optimizes pH as a critical parameter, maintaining it in a moderate range (8.5-12.5) rather than using extremely high pH values. This parameter optimization enables sufficient borate crosslinking activity while preventing polymer degradation and maintaining gel quality. The surfactant addition further enhances crosslinking efficiency at these moderate pH levels.
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 enables effective gel formation with reversible shear viscosity recovery at lower temperatures and persistent viscosity at elevated temperatures, maintaining gel strength and thermal stability.
Implementation Method 1
the borate crosslinker can gel the polymer fluid at a low temperature through a reversible crosslinking mechanism
Implementation Method 2
thereafter initiating a second gelling of the aqueous mixture with persistent crosslinking for low shear conditions, preferably after entry into the subterranean formation
Implementation Method 3
For early crosslinking of an ionic polymer in a low conductivity aqueous medium with a boron source followed by crosslinking at a higher temperature by a metal crosslinker, it has been found that surfactants with oppositely charged moieties can provide an adequate response to both borate and metal crosslinkers
Data Source
AI summary
Methods comprising preparing an aqueous mixture of an anionic polymer, a charge screening surfactant, and a borate crosslinker, wherein the mixture has a conductivity less than 10 mS/cm, injecting the mixture down a wellbore, and gelling the mixture. An embodiment of the aqueous mixture can also include tetramethylammonium chloride as a clay stabilizer and a metal crosslinker such as a complex of zirconium and an amino acid ligand system. An embodiment can effectively provide borate crosslinking of an anionic polymer in a low-ionic-strength fluid system, without sacrificing ultimate gel strength or thermal persistence of the metal crosslinked polymer.