After months of sub-optimal injection rates compared to offset wells, injection in an operator's well in a large oil field in India declined to almost zero. The wells in this field have traditionally been stimulated with high-rate bull heading of hydrochloric acid down the production tubing, however, post-treatment results using this technique have demonstrated inefficient stimulation due to permeability, porosity and pressure differences of the heterogeneous pay zones.

An innovative straddle packer system that uses two mechanically activated sealing elements was deployed for the first time in this basin to provide discrete stage isolation. The main objectives of introducing this high-rate, high-pressure straddle system was to perform multiple stimulation treatments, ensuring accurate placement in a single trip; thus minimizing intervention time.

The system used in the subject well was comprised of mechanical packers with double equalizing valves, a treating port, and a cleanout/debris removal section. The lower mechanical packer was set first in compression and the upper mechanical packer was then set in tension, creating zonal isolation for the straddled zone. At the same time, the treating port opened, enabling fluid flow from inside the workover pipe and into the straddle section. When the treatment was placed in the desired zone, the straddle packer was retrieved with the reversed procedure. The equalization ports enabled pressure and fluid communications between all sections, allowing the assembly to move up hole in preparation for the next stage.

This paper provides the decription of the mechanical straddle system, operational review and lessons learned during the first deployment of a novel straddle packer system in stimulating eight stages of an injection well. Comparative pre- and post-treatment results are discussed as a measure of treatment effectiveness. The paper also includes relevant notes on operational time optimization derived from the field implementation and comparison of other re-stimulation methods.

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