Abstract:

Surface viscous acid has been prepared by mixing thickening agent (PAM) and cross-linking agent (GL-5) with acid, which has the function of retarding reaction rate and sand prevention. At the beginning, the acid can retard the reaction rate by controlling the diffusion velocity of H+ in the body phase densification of the thickening agent. And with the consuming of H+, the acid can control sand and retard reaction further by forming gel film (surface thickening) on sand grain surface as a result of cross linking the thickening agent and cross linking agent under proper pH value (pH=3-5). The gel film is a good viscous-elastic material whose elasticity is stronger than its viscosity, and can wet the sand grain and adsorb on the surface of sand grain by hydrogen bond and electrostatic attraction. As a result, the motion of the sand grain is restricted. Also the film can control the diffusion rate of H+ further in order to retard the reaction rate and make the surface viscous acid reach the formation far away. The mechanism and effect of the acid for sand control have been evaluated and a new thinking that acidizing and sand control can be combined organically has been put forward in this paper.

Key words: surface thickener, viscous acid, sand control, retarded acid