Evolution of Well Completion Strategy in Deep High-Pressure Sour Environment to Enhance Rig-Less Operations & Optimize Rig Workover Operations

Deep critically sour fields played a key role in PDO's production portfolio for past two decades particularly in the south of Oman. Cost-effective solutions to develop these fields was certainly needed to ensure that oil produced from these fields is economically attractive. Completion design optimization was successfully implemented leading to significant savings in life-time cost of these well. Completion optimization journey was performed in stages based on the challenges encountered throughout the life of the field. Due to risky nature of the reservoirs in these fields, wells were completed with tubing and permanent packers to ensure well integrity requirements are fulfilled and all operation risks are controlled. These permanent packers induced a big challenge during well intervention & workover as they have low success chances when it comes to milling. This base completion design was optimized including eliminating the use of permanent packers to achieve savings of about 5% in well cost at least 80% in well interventions. At early stage of the field life, combining drilling caprock and reservoir section and casing them with the same liner was considered as a good saving in well drilling cost leading to total cost reduction of about 5% of total cost. However, this optimization increased cost of well intervention dramatically in these wells as the tubing and packer need to be retrieved to gain full access. In addition, challenges in milling the permanent packer have increased intervention cost even further. This first optimization done was to introduce a liner across the reservoir section of the same size as the tubing (Mono-bore completion). This optimization made the completion more Rig-less friendly and reduced well intervention cost by at least 80%. The second optimization done was to replace the permanent packers with Tie-back Polished Bore Receptacle (PBR). This has eliminated the requirement for packer milling without jeopardizing the sealing functionality of the permanent packer. This design was even optimized further to eliminate the possibility of failure of the permanent packer or PBR by introducing cemented completion. Cemented completion has also reduced total cost of drilling & completing the wells by 5% while maintaining the advantage to perform well activities and minimum cost. These improvements in well completion strategy have reduced life-time cost of the well dramatically without jeopardizing well basic functional requirements and well integrity requirement. As a result of this work, production from these field became more economically attractive.