pH-Sensitive Plugging Agent for Low-Permeability Reservoir Acidizing
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Solution Overview
Problem
Current temporary plugging agents used in horizontal wells have poor acid resistance and low plugging efficiency, leading to uneven acidizing fluid distribution, fingering, and reduced oil production, causing resource waste and economic losses in low-permeability oil reservoirs.
Innovation Solution
A pH-sensitive temporary plugging agent is developed, composed of carboxymethyl chitosan, gelatin, an initiator (AgNO3 in ammonia water), and carboxyl-terminated hyperbranched polyester, which forms a stable crosslinked structure that expands under acidic conditions and degrades with an alkaline solvent, minimizing damage to formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional temporary plugging agents are used, then plugging effect is achieved, but acid resistance is poor and plugging efficiency is low
Solution Approach 1:
The patent uses a composite material system consisting of carboxymethyl chitosan, gelatin, and carboxyl-terminatedhyperbranched polyester crosslinked through silver ion initiation. This composite structure provides both good plugging efficiency and strong acid resistance, resolving the contradiction between these two performance requirements.
Solution Approach 2:
The patent utilizes pH-sensitive parameter changes in the plugging agent. The carboxymethyl chitosan and gelatin components undergo conformational changes and swelling/deswelling transitions in response to pH variations, enabling the agent to maintain stability in acidic conditions while allowing controlled degradation in alkaline conditions for effective plugging.
2Duration of action of moving object
If conventional plugging agents are used, then temporary plugging is achieved, but degradation is slow and formation damage occurs
Solution Approach 1:
The patent employs pH-triggered parameter changes where the plugging agent remains stable in acidic oil reservoir conditions but rapidly degrades when exposed to alkaline degradation agents. This controlled parameter change enables fast degradation without formation damage, as the degradation process can be precisely timed and controlled.
Solution Approach 2:
The patent uses biodegradable materials (carboxymethyl chitosan and gelatin) that can be safely disposed of or degraded after serving their plugging function. These materials decompose rapidly under alkaline conditions, leaving minimal harmful residues compared to conventional synthetic plugging agents.
3Productivity
If acidizing fluid is injected, then acidification treatment is achieved, but uneven distribution and fingering occur
Solution Approach 1:
The patent introduces a pH-sensitive temporary plugging agent as an intermediary substance injected before the acidizing fluid. This intermediary forms a temporary barrier that controls and directs the acidizing fluid flow, preventing fingering and ensuring uniform distribution throughout the target formation zone.
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 pH-sensitive temporary plugging agent provides effective plugging and strong acid resistance, enhancing oil recovery by maintaining stability under acidic conditions and degrading easily with an alkaline solvent, thus reducing formation damage and improving resource utilization.
Implementation Method 1
the hydrophilic performance of free amino groups and carboxyl groups on the molecular chains of carboxymethyl chitosan and gelatin changes significantly, thereby showing different swelling properties as changes in pH
Implementation Method 2
could be degraded with alkaline solvent
Data Source
AI summary
A pH-sensitive temporary plugging agent and its preparation method, and the use thereof in exploitation of a low-permeability oil reservoir are disclosed. The temporary plugging agent is prepared by raw materials including, in percentages by mass, 3-8% of carboxymethyl chitosan, 0.2-0.7% of gelatin, 0.1-0.6% of an initiator, 5-15% of a toughener, and a balance of water, wherein the initiator is a solution of AgNO3 in ammonia water having a concentration of 0.1-0.3 mol/L, and the toughener is a carboxyl-terminated hyperbranched polyester.