A customized completion and perforation design was introduced and successfully applied in an onshore vertical well (carbonate reservoir) in Abu Dhabi, UAE. A new approach of running a 3-1/2" single zone completion string deployed with Tubing Conveyed Perforation (TCP) system was adopted, allowing perforation in an underbalanced pressure regime.

It is a standard practice in UAE to perforate the target reservoir zones in overbalanced condition, a condition in which the wellbore pressure is greater than the reservoir pressure, through wireline or pipe-conveyed gun before lowering the completion string. However, this typically results in near-wellbore damage (permeability impairment) that subsequently requires acid stimulation treatment for improvement in well productivity. Underbalanced pressure conditions can optimize perforations by minimizing the pore throat invasion in and around the perforation tunnels and prevents invasion of surrounding matrix by fine particles from the wellbore. However, selecting the minimum recommended underbalanced pressure with optimized gun configuration is a critical factor in achieving most favorable results based on reservoir rock type, permeability, and formation porosity.

During the course of design and selection, multiple methodologies were evaluated for completion and perforation, covering static underbalance perforation, overbalance perforation and dynamic underbalance conditions. A customized static underbalanced completion- TCP perforation design was applied in an appraisal well in Abu Dhabi with consideration for well control and other safety aspects. Post-perforation, the gun was released from the completion string and dropped below the pay zone to allow future interventions through fully opened completion tubing.

Enhanced well productivity was observed in the subject appraisal well, with an oil production rate that was around 4 times the oil production rate achieved in an offset well in the same field. This remarkable enhancement in productivity was obtained without any well intervention. A considerable cost saving of (+/- 0.5 million USD) was achieved by avoiding:

  • A separate trip for perforation prior to running the completion string,

  • Extended clean up period during well testing for a mature field reservoir

  • Acid stimulation treatment to reduce the wellbore damaged induced by overbalanced perforation

  • Well intervention through coiled tubing and N2 lifting to kickoff the well post stimulation

The paper will elaborate on the job design, focusing on parameters such as completion design, perforating gun system selection, perforating program to achieve the optimal productivity, gun release mechanism and contingency plans through this case study of the vertical appraisal well in Abu Dhabi. Additionally, the well control and safety aspects during completion and perforation gun installation, job execution details, and well testing results will also be covered. Way forward on further enhancement of well testing outcome through exploring other perforation criteria in upcoming appraisal & development well will be discussed in detail. A study of cost and time benefit analysis will also be part of the paper.

The successful application of the design has resulted in cost saving amounting half million dollars in well completion and perforation operations and achieved enhanced well productivity, underscoring the importance of innovative design and planning for maximizing gains.

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