Solid Retarded Acid Injection for Low Fracture Friction
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Solution Overview
Problem
Conventional high-viscosity retarded acid injection methods in oilfield development face issues such as high friction, shaft corrosion, high construction costs, and safety risks due to high viscosity, which complicates the process of creating long fractures in carbonate reservoirs.
Innovation Solution
A method involving the mixing of a non-reactive liquid with a solid retarded acid, where the solid acid is prepared by combining glycolic or lactic acid with natural polymers and zinc acetate, then coated with a polyglycolic acid film, allowing for low viscosity, low friction, and easy flowback, reducing construction costs and safety risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If high-viscosity retarded acid is used to reduce acid-rock reaction speed, then the acid fluid can reach deeper formations, but the friction in the shaft increases resulting in high construction pressure and low displacement
Solution Approach 1:
The patent changes the physical state of the acid from liquid to solid particles, fundamentally altering the flow characteristics. Solid acid particles suspended in low-viscosity fluid exhibit significantly reduced friction compared to high-viscosity gelled acid, enabling deep fracture creation with lower construction pressure
Solution Approach 2:
The patent introduces a suspension medium as an intermediary carrier that transports solid acid particles to the formation. This suspension system allows the acid to be delivered deep into the formation without the high friction associated with conventional high-viscosity retarded acids
2Length of moving object
If high-viscosity retarded acid is pressed into the formation under high-pressure conditions, then the acid can reach the target formation, but the construction cost increases and safety decreases
Solution Approach 1:
The patent reduces construction pressure by changing from high-viscosity liquid acid to solid acid particles in low-viscosity fluid. This parameter change allows the acid to be injected at lower pressures, improving safety and reducing construction costs while still achieving deep fracture penetration
Solution Approach 2:
The solid acid particles are designed as disposable carriers that dissolve upon contact with formation water, releasing the acid at the target location. This eliminates the need for expensive corrosion inhibitors and complex retrieval systems, reducing both cost and safety risks
3Duration of action of moving object
If high-viscosity retarded acid is injected into the formation, then the acid-rock reaction is retarded, but the residual acid has high viscosity causing difficulty in flowback and secondary damage to reservoir
Solution Approach 1:
The patent changes the viscosity parameter of the acid system from high to low by using solid particles in a low-viscosity suspension. This allows the acid to maintain retardation effectiveness during injection while enabling easy flowback after treatment, preventing secondary reservoir damage
Solution Approach 2:
The acid is segmented into discrete solid particles that can be independently controlled. These particles provide retardation during injection but dissolve separately upon contact with formation water, allowing the fluid phase to flow back easily without the drag of high viscosity
4Length of moving object
If high-viscosity retarded acid is injected through the shaft, then the acid reaches the formation, but the acid fluid contacts the shaft resulting in corrosion and shortening of service life
Solution Approach 1:
The patent extracts the acid from the liquid phase and converts it to solid particles. This separation removes the corrosive liquid acid from contact with the shaft during injection, as the solid particles can be suspended and transported without requiring the acid to be in liquid form throughout the injection system
Solution Approach 2:
The patent introduces a suspension medium as an intermediary that carries solid acid particles through the injection system. This intermediary protects the shaft from direct contact with acid, eliminating corrosion while still delivering the acid to the formation where it can react
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 method enables efficient, low-cost, and safe injection of solid retarded acid, reducing acid-rock reaction speed, allowing for longer fractures and improved conductivity, while minimizing corrosion and operational hazards.
Implementation Method 1
the acidic substance, i.e., glycolic acid (or lactic acid) of the solid retarded acid of the present invention is a strong acid, which can cause a dissolution reaction with carbonate rock
Implementation Method 2
spraying a glycolic acid aqueous solution having a concentration of 92 to 98% with a spray gun
Implementation Method 3
irradiating with an infrared lamp; after rotating for 10 to 30 minutes, spraying a glycolic acid aqueous solution
Data Source
AI summary
An injection method for a solid retarded acid includes mixing a solid acidic substance with a natural polymer, extruding through an extruder to produce particles; putting the produced particles in a coating pan, and sprinkling zinc acetate powder; turning on the coating pan to rotate while irradiating with an infrared lamp; spraying a glycolic acid aqueous solution with a spray gun, and continuing to rotate to obtain the solid retarded acid; injecting non-reactive liquid and the solid retarded acid into the a sand mixing truck; after the mixture is uniformly mixed in the sand mixing truck, injecting the mixture into a formation by a fracturing truck; conveying the solid retarded acid to a designated location, then stopping a pump, removing pipelines, and opening the well for gushing. The method is good in drag reduction, easy for flowback, thereby reducing the construction cost and facilitating environmental protection, and has broad application.