The Cement Packer completion has found great use and applicability in Chevron Nigeria assets by creating a cost-effective way of accessing ‘behind-pipe’ production opportunities. These isolated hydrocarbon pools could not have been otherwise developed due to the un-favourable cost of a Major Rig Workover. This has helped to maximize value from oil and gas assets by returning previously inactive wellbores to production. The typical through-tubing technique of deploying cement packers in candidate wells has been to set a plug in the tubing to isolate the deeper reservoir, punch a hole in the tubing, displace cement through the hole in the tubing and place it across the new target sand so that the displaced cement would serve as an artificial packer in the tubing-casing annulus. The tubing would then be perforated across the cement packer and into the target reservoir. Much success has been recorded with the use of this technique and though it has provided proper tubing-casing annulus isolation, there have also been a few challenges. Some of the challenges include significant skin (caused by the extra pressure drop during fluid flow through the cement tunnel), limited perforation efficiency in dual-string wells (caused by gun-size limitations due to the tubing size) and lack of radial flow since the perforations are oriented at zero-degree phasing to avoid perforating into the second string in dual-string wells. Eliminating these challenges would significantly improve the well production rate and project economics. This paper presents three case studies where these challenges have been effectively addressed and the attendant results. In the first case study, we show how over-displacing the cement ensured that the column of cement was placed above (rather than across) the proposed completion perforations while still retaining annular isolation. This significantly improved the expected initial production rate of the well by a factor of more than three since there was no extra skin due to fluid flow through the cement tunnel. In the second case study, we show how we improved the perforation efficiency in a dual-string well despite being constrained by the gun size by perforating twice at zero-degree phasing. In the third case study, we show how we overcame the challenge of always perforating at zero-degree phasing in dual-string wells by performing dummy simulations (at the surface) using pipe-in-pipe configurations to better understand the perforating gun orientation downhole relative to the tubings and casing. Based on the results of the surface simulations, we achieved additional phasing in two perforation runs and this significantly increased the productivity of the well. A major lesson learnt was the importance of performing dummy simulations at the surface using pipe-in-pipe configurations to mimic the tubings-casing configuration. This was crucial to the success of the job where additional phased perforations were added.
The changing landscape of global energy and fluctuations in commodity prices have driven companies to get more efficient means to sustain their businesses. With companies seeking more from their assets via rigless interventions, the trend has been that the low-hanging opportunities have been executed. The opportunities left are either too complex for rigless interventions or the expected production is too small to make major-rig workovers economic. We discuss such complex opportunities that were revisited to ensure sustained production from mature fields. The first case study discusses a gas-lift opportunity that was suspended when tubing leaks were discovered. The three holes posed a challenge since they were quite shallow and not suitable to be used as the injection-point of the gas. The work-around was to use a tubing patch to cover the holes without significantly reducing tubing ID as much as a pack-off would to allow for future well re-entry. The second case study discusses a well with a tubing restriction that prevented perforation addition. The job stalled when a gauge cutter (similar OD as the available gun) barely passed through the restriction during a dummy run. Even if the gun passed through and was detonated, the expended gun would be swollen and irretrievable due to the restriction. A modified perforating gun that disintegrated upon detonation was used, eliminating the need to retrieve the expended gun. The third case study was a well completed with mud five decades ago. The mud had caked; preventing any chance of executing a poor boy gas lift. The solution was to adapt the cement-bond-log technique to identify regions of moveable mud in the annulus with the mud subsequently displaced out by pumping. The lesson learned is that opportunities that have stalled due to their complexity can still be executed via rigless workovers by leveraging on existing technologies with slight adaptations to create well-specific solutions.
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