Thermoplastic Polyvinyl Alcohol Diverting Agents for Subterranean Flow Control
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Solution Overview
Problem
Current diverting agents for subterranean formations often fail to effectively divert fluids into lower permeability zones due to their permanence or require excessive efforts to remove, leading to temporary or permanent closure of productive sites.
Innovation Solution
Development of particulate diverting agents comprising melt-extrudable thermoplastic polyvinyl alcohol compositions, which are biodegradable and soluble in water, allowing for temporary plugging and easy removal after treatment, utilizing a polyvinyl alcohol resin with a specific degree of hydrolysis and plasticizer, and optionally additives like starch and fillers, to create pellets that can be effectively used in subterranean treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cements and solid slurries are used for physical plugging of high permeability regions, then the diverting effect is achieved, but the plugging material remains intact for extended periods or permanently, requiring extraordinary efforts to reopen productive sites
Solution Approach 1:
The patent applies parameter changes by selecting polyvinyl alcohol with specific degree of hydrolysis (88-99%) and molecular weight (10,000-1,000,000) to control the dissolution rate and diverting effectiveness. The material transitions from insoluble cement to water-soluble polymer, fundamentally changing the removal parameter from mechanical excavation to water dissolution
Solution Approach 2:
The patent employs disposable diverting agents made of water-soluble polyvinyl alcohol that perform their diverting function temporarily and then dissolve naturally. This eliminates the need for permanent plugging materials and the extraordinary removal efforts they require, allowing productive sites to be reopened easily by injecting water
2Ease of manufacture
If water-soluble materials are used as diverting agents, then easy removal is achieved, but the diverting agent may dissolve too quickly to provide effective temporary blockage
Solution Approach 1:
The patent precisely controls the dissolution rate by adjusting the degree of hydrolysis (88-99%) and molecular weight (10,000-1,000,000) of polyvinyl alcohol. Higher molecular weights and degrees of hydrolysis provide slower dissolution, extending diverting duration while maintaining water-solubility for easy removal. This parameter optimization balances temporary blockage effectiveness with removal ease
Solution Approach 2:
The patent creates composite diverting agents by combining polyvinyl alcohol with compatible additives and optional crosslinking agents. These composites maintain water-solubility for easy removal while the crosslinking provides temporary structural integrity to extend diverting duration before natural dissolution occurs
3Duration of action of moving object
If high molecular weight polyvinyl alcohol is used to extend diverting duration, then temporary blockage effectiveness is improved, but the viscosity and processing difficulty increase
Solution Approach 1:
The patent optimizes the molecular weight parameter to fall within 10,000-1,000,000, balancing diverting duration with processability. This parameter range provides sufficient molecular weight for extended temporary blockage while maintaining low enough viscosity for easy handling, mixing, and injection into formations
Solution Approach 2:
The patent introduces water-soluble crosslinking agents as intermediaries that temporarily enhance the structural integrity and duration of the diverting agent without requiring complex processing equipment. The crosslinking occurs in-situ in the formation, simplifying the overall processing while extending diverting duration
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 polyvinyl alcohol-based diverting agents provide a temporary and environmentally friendly solution by effectively diverting fluid flow between zones in subterranean formations, ensuring non-toxic and biodegradable properties, and are suitable for temperatures up to 250°F, facilitating easy dissolution and removal post-treatment.
Implementation Method 1
the polyvinyl alcohol in the diverting agent is substantially water soluble, the diverting agent dissolves over time in the wellbore and is ultimately removed after the subsurface treatment is completed
Implementation Method 2
melt-extrudable thermoplastic polyvinyl alcohol compositions
Data Source
AI summary
A biodegradable and substantially water-soluble thermoplastic polyvinyl alcohol-based diverting agent is provided which comprises pellets of a specified polyvinyl alcohol optionally with certain specified additives, which pellets are made in an extruder and cut to a specified size.