Development and Field Use of a Novel Solvent/Water Emulsion for the Removal of Asphaltene Deposits in Fractured Carbonate Formations

Abstract

Summary The formation of asphaltene scale inside the tubing or in the reservoir is a common problem associated with crude oils in many parts of Italy and is common to the industry as whole. In Italy, regular treatments with coiled tubing or washing by bullheading are performed to re-establish production. While asphaltene inhibitors can be injected into the tubing string, asphaltenes can still create problems below the injection point and plug the perforations, formation pores, and/or natural-fracture-network systems. There is a wide range of hydrocarbon-based solvents that have been used in the industry to remove asphaltenes. The more effective solvents have a low flash-point temperature, making them expensive and hazardous. In addition, these hydrocarbon-based solvents leave the formation in an oil-wet state after asphaltene removal instead of re-establishing the water-wet condition that acts as barrier to slow down the deposition of the asphaltene on the formation. This effect accelerates the redeposition of the asphaltene in the formation and increases the rate of the production decline, increasing the frequency of remedial treatments. This paper describes the laboratory development and field application of a water/aromatic-solvent emulsion system that has been used successfully to clean/dissolve asphaltene and leave the carbonate fractured formation in a water-wet state to delay the production decline. Other advantages when using this type of emulsion are cost reduction and improved effectiveness in removing asphaltene deposits, when compared to alternative solvents that have been used. This is of particular significance to those wells where large volumes of a washing phase have to be pumped down-hole. Hazards also have been reduced by using relatively high-flash-point aromatics. Continuous mixing of the emulsion when pumping reduces waste and improves the logistics involved in pumping the large volumes needed to treat long openhole sections and/or to treat the fractures deeper in the near-wellbore region. Two successful field applications in southern Italy will be discussed, describing the placement technique used and the results achieved with this new system. These treatments will be compared to previous treatments using a hydrocarbon-based solvent. In the first well where previous treatments had failed to make significant improvements, following the application of this emulsion the production was almost fully restored and the production decline was significantly slower than previous treatments. The second well treated was a long horizontal wellbore; again, the emulsion and technique proved successful in returning the production to previous levels and sustaining the new level for an extended period of time.