Polyurethane Proppant Coating for Fracture Conductivity
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Solution Overview
Problem
The challenge in well fracturing is the high flow back of proppants, which leads to reduced retention in the fractured well field and inadequate conductivity, particularly with polyurethane-coated proppants experiencing high flow back ratios and low coating levels that fail to maintain conductivity in small fractures.
Innovation Solution
A polyurethane coating process involving a homogeneous mixture of an isocyanate component, an amine reactant, and optionally an amine-based latent curing agent, which fully crosslinks to provide resistance to dissolution and flow back, ensuring the coating remains adhered to the proppant under downhole conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyurethane coatings are used to reduce flow back, then coating adhesion is improved, but flow back ratio increases and coating level decreases
Solution Approach 1:
The patent changes the chemical parameters of the polyurethane coating system by using specific isocyanate indices (120-240) and incorporating latent curing agents that activate at downhole temperatures. This modifies the coating's chemical structure to achieve both adhesion and resistance to flow back under reservoir conditions
Solution Approach 2:
The coating is applied at the surface with controlled composition and thickness (0.5-5 micrometers) before being deployed downhole. The preliminary coating application ensures proper adhesion while the latent curing mechanism activates later at temperature to prevent flow back
2Length of moving object
If coating level is reduced to permit entry into small fractures, then fracture penetration is improved, but proppant retention decreases
Solution Approach 1:
The patent uses temperature-activated latent curing agents that remain dormant during coating application and transport, then activate at downhole temperatures (above 50°C) to crosslink the coating in situ. This creates a thin but highly retentive coating that penetrates small fractures while preventing proppant flow back
Solution Approach 2:
The coating transitions from a flexible, uncured state during handling and transport to a rigid, crosslinked state downhole. This dynamic transformation allows the coating to adapt to different conditions: flexible enough for thin application but rigid enough for proppant retention under reservoir conditions
3Reliability
If phenol resin coatings are used to reduce flow back, then proppant retention is improved, but manufacturing cost and environmental impact increase
Solution Approach 1:
The patent modifies the chemical composition parameters by using polyurethane systems with specific isocyanate indices and latent curing agents, replacing phenol resins. This achieves comparable proppant retention with lower manufacturing cost and improved environmental performance
Solution Approach 2:
The patent employs a thin coating (0.5-5 micrometers) that provides sufficient performance for a single downhole application. The coating is designed to be cost-effective and environmentally friendly while fulfilling its retention function, replacing more expensive and environmentally problematic phenol resin alternatives
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 solution achieves a substantially cured polyurethane coating with low flow back and high crush strength, maintaining conductivity and reducing capital costs compared to phenol resin-based coatings, while being environmentally friendly and solvent-free.
Implementation Method 1
coating a proppant solid with a substantially homogeneous mixture of (i) an isocyanate component having at least 2 isocyanate groups, (ii) an amine reactant, and optionally (iii) an amine that is a latent curing agent for said isocyanate under conditions sufficient to substantially cure said proppant coating
Implementation Method 2
an amine that is a latent curing agent for said isocyanate under conditions sufficient to substantially cure said proppant coating
Data Source
AI summary
Solid proppants are coated with a phenol-urethane coating in one or more layers by a method comprising coating a proppant solid and then curing the coated proppant under conditions sufficient to substantially cure said proppant, wherein said coating comprises a substantially homogeneous mixture of (i) an isocyanate component having at least 2 isocyanate groups, (ii) an amine reactant, and optionally (iii) an amine that is a latent curing agent for said isocyanate.