The objective of this paper is to share the experience of how 7-5/8" section was drilled, and cased-off to enable the zonal isolation in the depleted VII horizon and high-pressure zone with close PPFG margins by managing high risks of differential sticking and loss of circulation at Bulla gas-condensate reservoir which is one of the most complex high-pressure fields with close PPFG margins in the world.

The Bulla wells are highly complex wells the Caspian region. Before drilling into the reservoir section which requires high MW, the drilling liner was run to the cased-off VII horizon and high-pressure zone, which have significant challenges such as differential sticking and loss of circulation, previously resulting in stuck pipe and losses. To overcome the challenges, under reaming/liner cementing at MW lower than PP were evaluated and applied to have good cementing across the open hole and good shoe, to drill into the reservoir section in the project.

The study helped to identify the issues and actions taken that resulted in significant improvement in well delivery and reduced the risks despite having underbalanced condition during under-reaming/cementing. So is accepting the bitter truth, situation offering limited sets of options was very challenging as having:

  • high risks of differential sticking and loss of circulation due to high MW,

  • high- pressure interval near the setting depth, which required high MW to stabilize the well,

  • need to isolate the high-pressure zone and depleted VII horizon for drilling into the reservoir section.

However, the operation plans of managing the ECD within limits by using different MWs, higher MW for running casing and lower MW for UR and cementing have been risk-assessed with all the mitigation, and as a result, the aforementioned intervals were well isolated which was supported by CBL results. No gains or losses were observed during the operations including both casing running and cementing. Finally, having a good cement in the shoe allowed to successfully drill into the reservoir section with high MW accomplishing successful completion of the well without any major problems previously occurring. Therefore, this approach not only reduced the time, cost and also helped to deliver the quality wellbore.

The case study of liner cementing at underbalanced conditions provides useful insights of how unconventional techniques can be successfully implemented to achieve the overall accomplishment in well delivery performance.

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