Polyacrylamide-Modified VES Fluids for High-Temperature Fracturing
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Solution Overview
Problem
Current viscoelastic surfactant fluids used in hydraulic fracturing have a temperature limit of approximately 121.1 °C (250 °F) beyond which their viscosity becomes unsuitable for fracturing applications, necessitating the development of formulations that maintain high viscosity at higher temperatures while reducing the amount of high-temperature viscoelastic surfactant (HT VES) usage.
Innovation Solution
The use of acrylamide-based polymers and copolymers, specifically polyacrylamides with a hydrolysis level of less than 5 mole percent and weight-averaged molecular weights ranging from 250,000 to 40,000,000 g/mol, is introduced to enhance the viscoelastic fluid's viscosity by attaching to HT VES micelles, thereby increasing the fluid's stability and viscosity at temperatures from 121.1 °C to 176.7 °C (250 to 350 °F).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the temperature is increased beyond 121.1°C (250°F), then the fracturing application capability is improved, but the fluid viscosity becomes unsuitable for fracturing
Solution Approach 1:
The patent combines viscoelastic surfactant (VES) with hydrophobically modified polymers to create a composite fluid system. The polymer component provides thermal stability and viscosity maintenance at high temperatures (121.1°C to 204.4°C), while the VES component provides the necessary viscoelastic properties for proppant suspension and fracture conductivity, resolving the contradiction between temperature capability and viscosity stability.
Solution Approach 2:
The patent modifies the physical-chemical parameters of the base fluid by incorporating hydrophobically modified polymers with specific molecular weights and hydrophobic group concentrations. This parameter change enables the fluid to maintain suitable viscosity across an expanded temperature range, allowing fracturing applications at temperatures beyond the conventional 121.1°C limit while preserving fluid stability.
2Quantity of substance
If the amount of high temperature viscoelastic surfactant (HT VES) is reduced, then the cost and complexity are lowered, but the viscosity at high temperatures decreases
Solution Approach 1:
The patent merges the functions of VES and hydrophobically modified polymers into a single formulation. The polymer component compensates for the reduced HT VES concentration by providing additional viscosity contribution and thermal stability, while both components work synergistically to maintain proppant suspension capabilities, thus reducing the required amount of expensive HT VES without sacrificing high-temperature viscosity.
3Stability of the object's composition
If the fluid viscosity is increased to maintain proppant suspension, then the proppant carrying ability is improved, but the pumpability and flow characteristics deteriorate
Solution Approach 1:
The patent utilizes the dynamic viscoelastic properties of the VES-polymer composite system. The fluid exhibits shear-thinning behavior where viscosity is high at low shear rates (maintaining proppant suspension in the fracture) and low at high shear rates (enabling easy pumping during injection). This dynamic property resolution allows the fluid to satisfy both proppant suspension and pumpability requirements through its ability to adapt viscosity based on flow conditions.
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 effectively lowers the amount of HT VES needed while maintaining similar viscosity, ensuring the fluid's stability and proppant suspension capabilities at elevated temperatures, thereby enhancing the effectiveness of hydraulic fracturing treatments.
Implementation Method 1
The viscoelastic fluid includes wormlike micelles that become entangled to form a 3-dimensional (3D) viscoelastic gel
Implementation Method 2
the viscoelastic fluid exhibits both elastic behavior and viscous behavior due to the micelles formed under different conditions
Implementation Method 3
When the viscoelastic fluid is subjected to shear stress, for example, by a pump, the viscoelastic fluid is shear thinned to produce a low viscosity fluid
Implementation Method 4
a hydrophobically-modified polymer
Data Source
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AI summary
In accordance with one or more embodiments, this disclosure describes a viscoelastic surfactant fluid for a subterranean formation comprising: brine solution; at least one polyacrylamide viscosity modifier with a weight averaged molecular weight (Mw) from 250,000 g/mol to 40,000,000 g/mol; and a viscoelastic surfactant according to formula (I): where R1 is a saturated or unsaturated hydrocarbon group of from 17 to 29 carbon atoms, R2 and R3 are each independently selected from a straight chain or branched alkyl or hydroxyalkyl group of from 1 to 6 carbon atoms; R4 is selected from H, hydroxyl, alkyl or hydroxyalkyl groups of from 1 to 4 carbon atoms; k is an integer of from 2-20; m is an integer of from 1-20; and n is an integer of from 0-20.