ABSTRACT
Significant decline in production performance has been observed during the first few years of production in some completions in Malaysian oil fields. Near wellbore damage is thought to be the cause of this decline. Acid stimulation is the method of choice in removal of near wellbore damage and has proven to be successful in removing about 50% of this impairment.
Stringent screening criteria for acid stimulation candidates have contributed to the success of the acid jobs. Two methods viz bullheading and coiled tubing are currently being practiced. Coiled tubing has been widely used since the start of the acid campaign in 1986 while bullheading was tried only recently. Both methods give comparable results with bullheading costing about half that of coiled tubing. Standard acid formulation common to the industry together with additives has given good results at certain optimum volume of acid pumped. Nitrogen or available gas lift gas has been used to kick-off the wells.
Post acid production performance has shown improvements as substantiated by PI increases up to 200%, better gaslift efficiency, lower skin factors and average gains up to 350 STB/D. However, 20% of the candidates (with gains less than 60 STB/D) were unsuccessful due to low remaining reserves and/or high pre-stimulation water cut during the first campaign. More stringent screening criteria such as low water cut and sufficient remaining reserves have helped to reduce the rate of failures in later campaigns to 15%.
