Seawater Fracturing Fluid Buffer System for High-Temperature Stability
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Solution Overview
Problem
Seawater-based borate crosslinked fracturing fluids face challenges at high temperatures due to precipitate formation and difficulty in adjusting pH, leading to reduced proppant pack conductivity and increased operational costs, especially in deep well fracturing operations where crosslinking occurs too early, causing friction loss and shear thinning.
Innovation Solution
An aqueous-based treatment fluid comprising a gelling agent, an aqueous base fluid, a buffer composition with a plurality of salts, and a crosslinking agent that delays crosslinking and maintains stability at high temperatures, preventing precipitate formation and ensuring high shear recovery, allowing for effective fracturing at greater depths with reduced injection rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the pH of the fracturing fluid is elevated to a level in excess of 9.5 to form a sufficiently crosslinked gel at high temperatures, then the gel viscosity is improved, but solid precipitates form that reduce proppant pack conductivity and productivity
Solution Approach 1:
A buffer system comprising carbonate and bicarbonate ions is introduced as an intermediary to control pH elevation. The buffer system allows the pH to increase to levels in excess of 9.5 necessary for high-temperature crosslinking while preventing the uncontrolled pH rise that causes magnesium hydroxide precipitate formation. The buffer acts as a mediator between the need for high pH and the need to avoid precipitation.
Solution Approach 2:
The invention changes the pH control mechanism from direct hydroxyl ion addition to buffer-mediated pH control. By using a buffer system with carbonate and bicarbonate ions, the pH can be elevated to the required level for crosslinking (pH > 9.5) while the buffer capacity prevents excessive pH rise that would cause magnesium hydroxide precipitation. This parameter change allows simultaneous achievement of high gel viscosity and precipitate-free fluid.
2Strength
If crosslinking occurs early in the pipe to achieve sufficient viscosity, then the gel strength is improved, but friction loss increases and pump pressures become excessively high
Solution Approach 1:
The buffer system is prepared in advance and incorporated into the fracturing fluid before pumping. This preliminary action ensures that pH control is established before crosslinking begins, allowing delayed crosslinking to occur. The buffer is pre-positioned to control the timing and rate of pH elevation, thereby controlling when crosslinking occurs.
Solution Approach 2:
The invention introduces dynamic control over the crosslinking process through the buffer system. Rather than crosslinking occurring immediately upon mixing, the buffer-controlled pH elevation allows the crosslinking to progress dynamically over time as the fluid travels through the pipe. This dynamic control enables crosslinking to occur at the optimal moment, reducing friction loss while achieving necessary gel strength.
3Productivity
If the pH is elevated using hydroxyl ions to achieve crosslinking at high temperatures, then the crosslinking efficiency is improved, but the reaction with magnesium ions is slow and time-delayed making pH adjustment difficult
Solution Approach 1:
The buffer system serves as an intermediary between hydroxyl ions and the crosslinking process. Instead of directly adding hydroxyl ions which react slowly with magnesium ions causing time delays, the buffer system mediates pH elevation through carbonate and bicarbonate equilibrium. This intermediary mechanism provides faster, more predictable pH adjustment while avoiding the slow magnesium hydroxide precipitation reaction.
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 treatment fluid maintains high viscosity and stability at temperatures above 200°F, preventing precipitate formation and ensuring effective fracturing with delayed crosslinking, reducing friction loss and operational costs, while maintaining compatibility with enzyme breakers and calcium and magnesium salts in solution.
Implementation Method 1
aqueous-based treatment fluids comprising a buffer composition... wherein the treatment fluid maintains a pH of about 10 or less when the treatment fluid is heated to a temperature of about 200°F or greater
Implementation Method 2
crosslinking agents such as borate ion releasing compounds can be incorporated into the fracturing fluids
Implementation Method 3
Another side affect of early crosslinking may be the shear thinning of the fluid as it passes through the pipe
Implementation Method 4
seawater contains multivalent ions such as calcium and magnesium ions which form insoluble precipitates at a pH greater than about 9.5... elevating the pH of the fracturing fluid to a pH greater than about 9.5 is difficult due to the formation of magnesium hydroxide
Data Source
AI summary
A method comprises providing a treatment fluid comprising a gelling agent, an aqueous base fluid, a buffer composition comprising a plurality of salts, and a crosslinking agent; and contacting a subterranean formation with the treatment fluid. The aqueous base fluid is preferably seawater and the buffer composition includes one or more salts present in the treatment fluid from about 1 to about 1000 pounds per gallon of treatment fluid.