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.
