Reviving a Fractured Water Injection Well:The First Use of Clay Acid Stimulation in Major Oil Field in Algeria

摘要

Berkine basin is one of the main oil producers in Algeria.Upper,Middle and Lower TAGI are the target oil bearing sands.The field ROD“GSA;Eni and Sonatrach joint venture”in this basin and shares by 60% of the total oil production.The field is pressure maintained mainly through water injection and gas injectors.The southern part“ROD Tail”has 4 water injectors targeting middle TAGI.On recent evaluation,through pressure measurement and interference test,reservoir pressure was found to decline by 35 bars within two years.This has prompted questions on reservoir management mainly the effectiveness of injector wells capacity in maintaining reservoir pressure.Extensive data were gathered through well intervention;clean out,perforation and reduced caliper.Many failed acid jobs were also noted on history of these wells.Quick fix solution such as Jet-Blaster operation via coiled tubing was executed without success to revive injectivity. In this paper,methodology and workflow adopted to identify the source of formation damage and scale deposition in the near well and perforation is presented.Solid samples were collected from the well and sent to laboratory to characterize formation damage type.The injection water was also analyzed by performing standard 12 ion analysis.Oli Scale Chem simulator was used to confirm that the water was supersaturated with(CaSo4)&(CaSo4.2H2O)and likely to precipitate.Finally,clay acid as treatment fluid was found to be most effective in eradicating the clay deposits in the nearwell bore region identified by XRD from the solid samples collected.The treatment fluid was also designed to prevent proppant dissolution and cleaning frac matrix interface.This was the first time to execute such operation after many unsuccessful conventional acidizing operations. Excellent post acid stimulation treatment results were obtained.Injection rate was found to increase significantly from 120 m3/d to 360 m3/d.Water injection pressure was also found to decrease from 243 bar to 220 bar,injectivity index increased by 3 times.Near wellbore formation damage is removed and formation permeability recovered.The application of Clay Acid treatment was replicated to other wells in the field and similar results.