Ensuring Zonal Isolation During Abandonment with an Innovative Coiled Tubing Placement Technique

Abstract

A flowing or pressure-sustained annulus is a live threat to the environment, population, vegetation, and natural habitat. In the current oilfield environment under strengthened regulations from regulatory authorities, zonal isolation must be assured before completely abandoning a well. In the west region of Sumatra, Indonesia, a large number of shallow injector wells are drilled; after passing a certain age and productive life, they are abandoned. Most of these wells have lost circulation and therefore need a cost- and time-efficient cement placement method that can demonstrate zonal isolation by means of cement bond logs. The conventional cement placement method across the perforations requires several steps: placing cement, squeezing, leaving the cement on top of the perforations, waiting on cement, drilling the cement, and running the cement bond log. A novel squeeze method was deployed as a solution by combining a chemical contaminant and a squeeze technique. The objective was to perform the cement bond log directly after wait on cement without spending time to drill out the cement. In this technique, cement was placed using a coiled tubing pump-and-pull method: A squeeze was performed in the perforations; then coiled tubing was run into the well below 30 ft of perforations and an engineered contaminant fluid was pumped to contaminate the cement in the tubing. After the recommended wait- on-cement time, the cement bond log was run to confirm zonal isolation across the perforations. This technique eliminated the need to drill the set cement in the slim tubing, saving several days of work time. In most of the wells, the cement bond log showed less than 5 mV, which helped to determine the achievement of zonal isolation. Furthermore pressure tests were conducted to ensure the zonal isolation across the perforated intervals. Engineered cement and contaminant design is required to ensure cement will gain and maintain designed mechanical properties behind the tubing. This paper will discuss the case histories from six wells in the west region of Sumatra field, where the novel coiled tubing placement technique has been applied and proven successful and cost-effective.