This paper will present a field case study to clean out wellbore organic deposits using a high flash point emulsified solvent system. Wellbore organic deposition was present in a horizontal water injector, Well-X, at 140 feet (ft.). The water injector is a pilot well completed above a tar mat formation to provide reservoir pressure maintenance. The wellbore deposits have restricted wellbore accessibility and caused loss of injection potential. Downhole samples from the obstructing material were collected from the wellbore using a wireline bailer. The samples were analyzed in the laboratory using solvent extraction and infared spectroscopy. The downhole samples were found to be comprised mostly of maltene which was present in the form of saturates, aromatics and resins at varying weight percentages. The organic deposits also contained asphaltene.
The wellbore organic materials underwent extensive solubility testing at a simulated downhole temperature. Several solvent systems were evaluated such as xylene in diesel and aromatic solvent systems. Based on the performance of the dissolution systems in terms of solubility and soaking time an emulsified solvent system comprising n-methylpyrrolidone, fresh water, emulsifier, and an aromatic solvent was chosen for field deployment. Other factors such as chemicals hazards and cost were also considered as part of the treatment fluid selection process.
The treatment fluid deployment was carried out using both the bull heading and coiled tubing (CT) techniques to ensure full exposure of wellbore organic deposits to the emulsified solvent system. The treated deposit solutions were flowed back using zero discharge system and their organic contents were inspected periodically. The field treatment design, job execution, contingencies, and what-if scenarios will all be discussed in this paper.