Abstract

Well Intervention operations are carried out to improve production performance of a declining well, restore production to a well that quit, or improve well integrity, among other reasons. Well bore clean out and stimulation are two of the common well intervention operations done on producing oil and gas wells to improve performance. Well AA, a major oil and gas producer started to decline after three years of production, therefore a well bore clean out and stimulation exercise was designed to improve performance of the well. The first Intervention operation was planned after various crude sample and precipitate analysis reports showed organic deposits (wax and asphaltenes) in the well. Slickline drift also indicated a restriction in the tubing. The treatment recipe for the well intervention was designed based on laboratory test carried out on the crude and precipitate sample that showed an 85% dissolution of the organic deposits in Xylene and 55% dissolution in Solution Z (a mixture of Xylene and HCL). The 85% dissolution was considered adequate to ensure a complete wellbore clean out, with Solution Z planned as the contingent treatment recipe for any solid deposits not dissolved by Xylene. Contingent on the successful wellbore clean out, a matrix stimulation was to be done using an Acid preflush and Regular clay acid as the main treatment. But this operation failed because instead of resulting in an increase in production, the well couldn't produce to surface and had to be shut-in. This paper will review the problems encountered from the unsuccessful intervention of well AA because of the lack of a detailed recipe design to find the best treatment to dissolve organic deposits in the well and precipitates, as well as residues formed from the reaction between organic solids and inorganic acids. In addition, this paper will present the detailed work that went into designing the right treatment recipe for well AA that resulted in successfully reviving the well after the initial failed intervention operation to become a prolific producer of over 1500 stock tank barrels of oil per day.

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