Challenges of drilling Iran’s deepest surface hole in the saddle section of Changuleh oilfield with complex structure and pressure regimes

This paper presents a novel case study on successfully drilling the deepest surface hole in the Changuleh Oilfield in western Iran. The well between the Changuleh and Azar anticlines posed significant challenges due to its complex geological formations and high-pressure regimes. The main goal is to evaluate the hydrocarbon potential of the Sarvak Formation, analyze its connection with Azar structures, and identify the water and oil interface. An optimized combination of drilling techniques was employed to overcome these challenges, including strategic alternation of tri-cone and PDC bits, tailored drilling fluid design, and continuous wellbore stability monitoring, significantly reducing non-productive time and improving drilling efficiency. The average penetration rate was 2.13 m per hour, achieved under challenging conditions characterized by complex geological formations and high-pressure regimes. While this rate indicates operational efficiency, it is important to note that the drilling team continuously managed various challenges, including maintaining wellbore stability and optimizing drilling parameters to mitigate potential drilling issues. The study highlights the importance of optimizing drilling fluid design and continuously monitoring wellbore stability to overcome challenges posed by complex geological formations. According to geomechanical studies, seven drilling sections are optimal for accessing reservoir layers in this field. The drilling program has achieved a significant milestone by reaching a depth of 2200 m in one of Iran's most challenging Oilfields. The installation of a 20-inch surface casing, which is a significant accomplishment in their operations, demonstrates the success of the drilling program. This case study aims to thoroughly analyze the engineering and operational aspects of drilling, running, and cementing the country's deepest and heaviest surface casing. Specifically, it aims to provide insights into the successful execution of drilling operations in complex geological formations and high-pressure environments. Tri-cone bits significantly improved penetration rates compared to previous drilling operations in the field, with average rates ranging from 0.5 to 0.8 m per hour. Using PDC bits for the first time in this well also resulted in higher drilling progress rates. These findings suggest that these novel techniques can be applied to similar drilling operations to improve drilling efficiency and reduce non-productive time.