| Popis: |
A procedure is presented by which increased oil recovery from vertically heterogeneous reservoirs during gas flooding and/or elimination of the impacts of gas coning in gas-cut wells can be achieved. In this procedure, sodium chloride-saturated brine is injected into the layered, heterogeneous reservoir causing flood mainly in its more permeable zones. When the quantity of the solvent (water) and/or the solubility of the salt is diminished, salt crystals will precipitate in the pores of the reservoir. The crystals block mostly the more permeable parts of the reservoir which may result in reduced reservoir heterogeneity and - consequently - volumetrically more entire gas (e.g. carbon dioxide) flooding of the reservoir. The procedure, resulting in selective profile modification ensures more effective oil recovery by increasing the volumetric sweep efficiency. A field-scale project was prepared for a heterogeneous sandstone reservoir in Hungary that had been previously developed by CO2 drive. The economical estimation indicates a positive result. Similar selective profile modification can be attained in oil-producing wells having unfavorable gas production caused by gas coning. The gas-cut pay zone can be blocked by in situ salt precipitation and the oil production of the well can be restituted. A successful gas coning elimination was carried out in the sandstone reservoir of Algyő field, Hungary. Gas coning was observed in the well, which was able to produce oil only periodically before the treatment. The well continuously produced 7400 m3 (46500 bbl) oil after the treatment including 3050 m3 (19200 bbl) excess oil recovery. In 2002, successful gas coning elimination was performed on four wells. (One of them was horizontal.) Further treatments are planned on five wells in 2003. |
