Matrix acidization job design

Abstract

To maintain pressure control during drilling, completion or work over of a well the operations are usually done at overbalanced condition, these overbalanced condition results in influx of fluids and solids from wellbore into formation. The net effect of invading fluid interaction with formation is generally detrimental. The result is near wellbore formation damage causing additional pressure drop in the vicinity of wellbore and a reduction in well productivity. Acidizing is a matrix treatment that is carried out at a pressure lower than the formation breakdown pressure whereby acid is injected into the formation to improve well productivity. The type of acid to be used depends on the type of formation. Well stimulation techniques are applied on regular basis to enhance productivity and maximize recovery in oil and gas wells. Among these techniques, matrix acidizing is probably the most widely performed job because of its low cost compared to hydraulic fracturing, and suitability to both generate extra production capacity and to restore original productivity in damaged wells. The principal involves injecting an acid solution into the formation at a pressure below the fracture pressure with the primary objective of removing damage near the wellbore, hence restoring the natural permeability and improving well productivity. Reservoir heterogeneity plays a significant role in the selection and design of acidizing treatment. The success of acidizing treatment is strongly related to dissolution pattern of matrix. The standard acid treatments are HCl mixtures (to dissolve carbonate minerals) and HCl-HF formulations to attack plugging minerals, mainly silicates (clays and feldspar).