Novel Acid-Diversion Technique for Matrix Acidizing in Production and Injection Wells: Case Histories of Algeria

摘要

Successful matrix acidizing requires an even distribution of the acid treatment to remove near-wellbore formation damage throughout the perforated interval. In the absence of diversion, acid treatments tend to predominantly enter the highest- permeability zone, thus bypassing the lower-permeability, or most damaged, layers. In some cases, the acid might also break into a nearby water-bearing zone, which can result in a significant increase in water production after the treatment. This paper presents the field implementation of an associative polymer (AP) system that has been used to effectively divert matrix acid- stimulation treatments in producer and injector wells in an Algerian oil field. Additionally, this AP system can potentially reduce formation water production or redistribute water in injectors. The AP system is placed as a low-viscosity solution (< 2 cp) in alternating stages with the acid throughout the entire treatment. This AP system immediately adsorbs to the surface of the rock, reducing formation permeability to water with little or no effect on the permeability to hydrocarbons. The subsequent acid stages are diverted to other zones because the aqueous-based acid treatment will find a restriction in the zones where the AP chemical has been adsorbed. It does not rely on viscosity or solids to provide diversion (unlike the plugging mechanism of typical particulate diverters). Case histories are presented of producer and injector wells where this novel acid-diversion technique positively changed oil production, including a case where water production was decreased from 75 to 60%. The acid-stimulation treatments included alternating stages of acid (9:1 hydrochloric:hydrofluoric[HCl:HF]) and the AP system. More than 1,100 jobs have been performed worldwide with the AP system in sandstone and carbonate formations up to 350°F. This technique has been implemented in matrix and frac acid treatments.