First Application of Underbalanced Drilling in Fractured Carbonate Formations of Iranian Oil fields Leads to Operational Success and Cost Savings

Abstract

Abstract Underbalanced drilling techniques (UBD) are evolving at a fast pace as oil companies learn how to use the technology to maximize well production and lower finding costs. Although there was some air drilling through surface drilling activities in Iran for the past decade, the full package of UBD equipment and other UBD techniques were not introduced until National Iranian Oil Company (NIOC) supplied the package for a pilot project in southern Iran. The first well selected to be drilled UBD was GS 333, the reason for selecting that particular well was because the Gachsaran field is depleted and sever mud losses is experienced while conventional drilling, also, the UBD technique is expected to increase productivity of the well by decreasing formation damage resulted from drilling fluid losses. The drill pipe injection technique was proposed to be utilized in this well because of its suitability for the well conditions where it is not expected to drill through the gas cap and the well will be completed in 8 ½" open hole. This paper discusses the well design, UBD design parameters, Underbalanced modeling considerations and the lessons learned from this job which all led to the success of this project. It is also describe the process used to address HSE issues of the project in the face of the potential presence of H2S while drilling. The drilling and production results that were achieved were significant to the future operational potential and viability of this mature field. Of equal importance was the success of the operation from a health, safety and environmental (HSE) perspective in an environment in which the industry has been traditionally reluctant to use UBD techniques.