Removing Mechanical Skin in Heavy Oil Wells

Abstract

Abstract High-amplitude, low-frequency pressure pulsing was developed as a new oil well workover technique, and has been used in > 40 heavy oil wells in Alberta and Saskatchewan during the period October 1998 to October 1999, with a good success ratio. The method is particularly effective in initiation sand production and in cases where mechanical skin arising from blocked perforations, immobilized fines and asphaltenes are responsible for a high skin factor. Perforation blockage, restriction of near-wellbore flow paths through fines accumulation, pore throat precipitation of asphaltenes, and sand re-compaction around the well are all thought to be responsible for rapid production rate declines in many wells. In heavy oil wells, chemical treatments alone are rarely useful, but large physical perturbations of the material around the wellbore have been found to be effective in reestablishing production. A downhole device was developed to apply large periodic pressure pulses to the perforation face. This device also permits injection of fluid at measured rates into the nearwellbore region while executing prolonged (9–12 hour) high-amplitude perturbation. The action loosens mechanical skin, allowing the source of flow blockage to be physically removed through remolding and liquefaction of the sand around the wellbore. This liquefied zone is produced when the well is placed back on production, and in most cases the well is rejuvenated. In some cases, wells that never produced economic rates of oil because sand influx could not be initiated were turned into reasonable producers after a pressure pulse treatment. The method can also be used to deliberately introduce treatment chemicals while reducing the negative effects of channeling and fingering, as the front of treatment fluid ingress is well dispersed by the pressure pulsing.