Chemical Diversion Techniques Used for Carbonate Matrix Acidizing: An Overview and Case Histories

Abstract

Abstract The purpose of matrix treatments in carbonate reservoirs is to increase connectivity of a formation with the wellbore in the entire zone of interest. Successful matrix treatments depend on the uniform distribution of the treating fluid over the entire interval. When fluids are pumped into a well, they naturally tend to flow into the zone with the highest permeability or least damage. Field experiences showed that there is no assurance of complete zone coverage without proper diversion. Therefore, diversion is recommended in all treatments, especially in extended reach and multi-lateral wells. Diversion techniques can be classified as mechanical or chemical. Mechanical control of treating fluid placement can be accomplished by coiled tubing with an inflatable packer, or with conventional straddle packers or ball sealers. Although mechanical techniques are very effective, they are more expensive and time consuming than chemical techniques and they are often not applicable or not effective in wells with open-hole completion. More importantly, mechanical means diverts treatment fluids from the wellbore; however, there is no control once the fluid enters the formation. Chemical diversion can be achieved through placing a viscous fluid, foam or gel to lower the penetration of treatment fluid in the created wormholes and their surrounding matrix, or a particulate carrying fluid, which creates a filter cake on the surface of the wormholes. This filter cake results in temporary skin effect which alters the injection profile. Gelled and foamed acids are also being used as a means of improving acid placement by combining stimulation and diversion in one step. Diversion is a critical step to ensure the success of matrix acid treatments. Understanding how chemical diverters interact with the formation rock and fluid is the key to selecting the proper product for a specific treatment. It is the intent of this paper to provide a technical overview of mechanical and chemical diverters used in the oil industry. The various mechanisms by which these chemicals to achieve acid diversion, their application histories, and their limitations are presented. This paper provides guidelines for production engineers to optimize the fluid placement.