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An organic deposit cleanout job was successfully performed on a horizontal openhole Arab-D reservoir oil well and a high oil rate was restored from the dead well. The well was treated with a proprietary chemical solvent using bullheading and coiled tubing (CT) jetting technique to have maximum coverage of the wellbore from the tubing to long open hole horizontal sections. The treatment performed for this job representedthe first application of this chemical in a carbonate field of North Ghawar. A few wells in this area, lying within the boundary of a gas cap, have experienced asphaltene/paraffin problems that resulted in productivity decline and wellbore inaccessibility. A high gas-oil ratio (GOR) has been thought to be the main reason for asphaltene/paraffin precipitation inside the wellbore and near the formation. Organic depositswere observed to have accumulated in the wellhead and shallow tubing depth. This well was drilled in 2007 on the periphery of the south gas cap of the field and died after being on production for three years at a relative low watercut. The well was reported with a high GOR and water cut around 2% to 3% before dying. Analysis of a downhole sample confirmed 100% hydrocarbon with 81% asphaltic presence. The asphaltene/paraffin deposition was identified as the main reason for the death of this well. Chemical/solvent treatment using a CT jetting/pulsating mechanism was employed to have a maximum benefit. The solvent was proven in the lab to be very effective in dissolving asphaltene/paraffin and had a higher flash point. The job was performed in two stages. In the first stage, about one tubing volume of the solvent was bullheaded and left for soaking for 24 hours. In the second stage, the solvent was placed using 2" CT in the open hole section. This paper describes in detail the nature of the asphaltene problem in this area, the formation mechanism, treatment selection, design and execution, and future prevention approach to avoid recurrence. |
