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Diverting acid system
2025-04-01
A diverting acid system is a specialized fluid used in oil and gas well stimulation to control the flow of acid into specific zones of a reservoir. This ensures that acid treatment is directed toward areas with lower permeability or damage, thereby enhancing the overall effectiveness of the stimulation process.
Composition of Diverting Acid Systems:
Acid Solution: Typically, hydrochloric acid (HCl) is used as the primary acid for carbonate formations, while hydrofluoric acid (HF) may be employed for sandstone formations.
Diverting Agents: These are substances added to the acid to temporarily block high-permeability zones, forcing the acid to flow into lower-permeability areas. Common diverting agents include:
Viscoelastic Surfactants (VES): These surfactants form a gel-like structure that increases the viscosity of the acid, aiding in diversion.
Foaming Agents: These agents generate gas bubbles within the acid, creating a foam that can block high-permeability zones.
Emulsifiers: These chemicals form emulsions that can act as diverting agents by creating a barrier between the acid and the formation.
Corrosion Inhibitors: Added to protect the wellbore and equipment from acid-induced corrosion.
Breakers: Substances that reduce the viscosity of the diverting agents after the treatment, facilitating cleanup and flowback.
Importance of Viscosity Parameters
Viscosity plays a crucial role in the performance of diverting acid systems:
Control of Acid Flow: Higher viscosity helps in diverting the acid to targeted zones by reducing its ability to flow into high-permeability areas.
Enhanced Treatment Efficiency: Increased viscosity can improve the contact time between the acid and the formation, leading to more effective stimulation.
Self-Diversion Capability: Some diverting acid systems are designed to increase viscosity as the acid reacts with the formation, promoting self-diversion. For example, Baker Hughes' Divert HT acid systems have low viscosity in concentrated HCl acid, but viscosity increases as the acid spends, enabling more complete and efficient treatment of formations with varied permeability.
Shear-Thinning Behavior: Many diverting agents exhibit shear-thinning properties, where viscosity decreases under high shear rates (such as during pumping), allowing for easier placement. Once the shear rate decreases in the formation, the viscosity increases, aiding in diversion.
the composition of a diverting acid system is carefully selected to balance the need for effective diversion with the ability to clean up and flow back after treatment. Viscosity parameters are critical in achieving this balance, influencing the system's performance during and after the stimulation process.
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