Abstract
As part of the second stage development of a mature oil field offshore Malaysia, deeper reservoirs in Field S were identified from four different blocks. In order for the wells to be economically viable, up to eleven (11) sands were planned to be completed. This proved to be challenging due to the high differential pressures between reservoirs, highly depleted zones above the target sands, and pressure and reserve uncertainties of the target sands.
This paper covers design, planning, and execution of the well completion for four (4) infill wells where the differential pressure between zones was predicted to be up to 1,700 psi (Pounds per Square Inch). Some of the zones were highly depleted, and the most depleted zone was 0.216 psi/ft (Pounds per Square Inch per Foot). Even with the lowest brine weight of 8.5 ppg (Pounds per Gallon), the over balance was about 1,800 psi.
The completion was designed to maximize the number of sands in each well (eleven (11) sands with six (6) zones) to gain maximum production, while at the same time the short string needs selectivity. One of the challenges was the production casing design could not be larger than 7". To facilitate selectivity on the short string, the upper completion was designed with a Y-block.
To avoid significant losses from high overbalance and differential pressures, stage-by-stage perforation was planned. However, the challenge was to achieve the required under balance across all the zones since there was no stimulation planned. Both static and dynamic under balance perforation techniques were used for perforation.
With all the upfront planning and design, the well completion operation was successfully executed with less than 1% Non Productive Time (NPT) recorded, which was an excellent achievement considering the complexity of the completion design and operation.
In conclusion, the post-analysis showed the production rate target was successfully attained - indicating the formation damage was minimal even though the wells were drilled and completed with more than 1,000 psi overbalance.
