Comparison of Using Combination of Acetic Acid and Hydrochloric Acid with Only Hydrochloric Acid as Matrix Pre Flush

Matrix acidizing is a stimulation technique commonly applied to sandstone reservoirs to remove near wellbore skin damage and improve well productivity. For any acidizing process, the selection of acid (formulation and concentration) is very important. Mud acid has been successfully used to stimulate sandstone reservoirs for a number of years. It is a mixture of hydrofluoric (HF) and hydrochloric (HCl) acids designed to dissolve clays and siliceous fines accumulated in the near-wellbore region to re-open or enlarge microscopic flow paths and thus improve formation permeability. The success of acidizing depends to a great extent upon proper acid selection and good treatment design. There are mainly three stages in acidizing process i.e., pre flush, main acidizing, after flush treatment. The results of acidizing depends on all these stages. For effective acidizing process best acid combination should be used in these stages to ensure that the permeability and porosity change is maximum. In this paper combinations of (HCl and CH3COOH) had been used and compared with the standard acid combination (15% HCl for the pre flush stage). As this stage is the initial stage and the main function of the acid should be to remove the carbonates present in the formation and also to remove the Na and K ions.