Coated Proppants Reducing Flowback in Hydraulic Fracturing
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Solution Overview
Problem
Proppants used in hydraulic fracturing often experience flowback, where they are washed out of fractures, leading to reduced production rates and equipment damage due to their abrasive nature, and existing polymer coatings do not adequately prevent this while maintaining permeability.
Innovation Solution
A method of coating proppant particles with a polyisocyanate and starch mixture, reacting at elevated temperatures to form a solid polymeric coating that prevents flowback while maintaining permeability, using a urethane catalyst to simplify the coating process and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polymer coating is applied to proppant particles to reduce flowback, then flowback resistance is improved, but the coating process becomes more complex and costly
Solution Approach 1:
The patent uses a composite coating system combining polyisocyanate polymer with starch additive. The starch serves as a filler and bonding agent that enhances the coating's adhesion to proppant particles and rock formation, while the polyisocyanate provides the polymeric matrix. This composite approach improves flowback resistance through synergistic effects without requiring complex multi-step coating processes.
Solution Approach 2:
The patent modifies coating parameters by using pre-emulsified starch and controlling the curing temperature and time. The starch emulsion allows for better distribution and adhesion at lower concentrations, while the curing process at elevated temperatures (up to 150°C) activates the polyisocyanate-starch reactions to form strong bonds. These parameter optimizations simplify the overall coating process while maintaining high flowback resistance.
2Stability of the object's composition
If proppant particles are coated to prevent flowback, then proppant stability is improved, but permeability of the formation may be reduced
Solution Approach 1:
The coating is applied as a thin layer on the surface of proppant particles rather than as a thick bulk material. This localized application provides flowback resistance at the particle surface while maintaining pore spaces between particles for fluid flow. The starch component specifically enhances surface adhesion to rock formation without significantly increasing coating thickness, thus preserving formation permeability.
3Ease of manufacture
If starch is used in the coating composition, then coating simplicity and cost are improved, but reaction control becomes more challenging
Solution Approach 1:
The starch is pre-emulsified before being mixed with the polyisocyanate coating composition. This preliminary emulsification step ensures uniform distribution of starch particles throughout the coating, preventing clumping and ensuring consistent adhesion properties. The pre-emulsified state also controls the reaction rate by regulating starch accessibility to the polyisocyanate, making the curing process more predictable and easier to manufacture.
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 coated proppants are free-flowing during handling, pack well in fractures, and bond strongly under pressure, significantly reducing flowback and maintaining effective oil and gas flow, with a simplified and cost-effective coating process.
Implementation Method 1
reacting at least a portion of the polyisocyanate with at least a portion of the starch at the surface of the substrate particles in the presence of a urethane catalyst at an elevated temperature of up to 150° C. and for a period of up to 10 minutes to produce the solid polymeric coating
Implementation Method 2
in the presence of a urethane catalyst at an elevated temperature of up to 150° C. and for a period of up to 10 minutes
Implementation Method 3
applying at least one polyisocyanate and starch to the surface of solid substrate particles
Data Source
AI summary
Coated proppant particles are prepared by coating the particles with at least one polyisocyanate, and at least one urethane catalyst, and starch is present during at least part of the curing step. The starch becomes incorporated into in at least a portion of the cured coating. The coating cures rapidly at moderate temperatures, and bonds to itself well under conditions of heat and pressure as are experienced by the particles in subterranean formations.