First Experience Matter: The Valuable and Great Learnings from Unfavorable Mud Acid Stimulation in S Field Gravel Pack Wells, East Malaysia

Abstract

Abstract Most of the S oil field producers experienced rapid decline in production and this is suspected due to fine sediment particle migration and plugging. The S field team had carried out external formation damage study as they have no expertise and field experience to determine the damage mechanism and evaluate the best acid treatment recipe for their formation damage. Recently, mixtures of traditional hydrochloric and hydrofluoric acids have been used for the removal of near-wellbore damage in S field sandstone formations. The stimulation campaign in this field which has turbidite reservoir, high clay content predominantly by kaolinite and illite with high siderite mineralogy applied both bullheading and coiled tubing squeezing techniques. The treating fluid selection is highly dependent on mineralogical data and laboratory works. Based on the core flood testing performed, high strength mud acid is chosen as the main treatment fluid and gave superior result in permeability recovery as compared to milder organic acid and HF. Unfortunately, the actual field stimulation turned out to be opposite from the core flood testing outcomes. The situation is worsened in multistage treatments, which traditionally involve many repeat stages of preflush, main treatment, overflush and diverter. The mud acid stimulation prompted more water production and fine migration that is ended up with production curtailment. Only one out of four of the treated candidates resulted significant gain after gas lift valve change took place. This paper also will outline the reviews on results of laboratory testing and field actual performance together with the recommendations for future improvement. Stringent candidate selection, improved treatment fluids cocktail, operational challenges such as unanticipated longer flow back period, post treatment unwanted precipitation, ineffective diverter placement and skin build up post treatment are among of the learning points captured in this paper. From this unfavorable mud acid stimulation campaign which cost USD4million value leakage, our team comes out with best practices for future stimulation and key learning to share with industry colleagues who has no field background to combat with fine migration issue in their sandstone asset. Laboratory works is not the only paramount to any stimulation, success in stimulation is a journey, not a destination. The doing is often more important than the outcome.