Fracture Gas Reservoir Drilling Campaign - Challenges and Lessons Learnt from Suban Field in Indonesia: Case Study Suban-X

Abstract

Abstract Suban Field was discovered in 1972 and has been abandoned until 1998. The fracture reservoir has a characteristic high permeability compared to the matrix reservoir. This special characteristic is causing losses in drilling at the reservoir section. In the early drilling campaign (1972 – 2006), conventional drilling (loss and cured) was applied to overcome the challenge. However, this method has prolonged drilling time and caused high skin in terms of reservoir productivity. Since 2010 until now, Managed Pressure Drilling (MPD) had been applied to optimize drilling time and resulted in less skin to have good reservoir productivity. During this period, there are some challenges in MPD application especially due to depleted reservoir pressure (~6 ppg EMW) forcing the engineering team to optimize the creative design that aligned with project optimization without jeopardizing the operation. In the early stage of MPD drilling campaign, a downhole valve was installed as a mechanical wellbore isolation tool while tripping in/out when losses occur. The performance of downhole valve has been evaluated from the last 5 wells drilling campaign before drilling Suban-X well with a statistical evaluation showing 6 successful isolations out of 18 total attempts. Some experiments were performed when the downhole valve was not closing properly on the last 3 wells during the Drilling and Completion campaign. The experiments were successful to suppress the gas by bull heading the well with a sufficient rate of water, periodical high viscosity sweep injection as a precaution for gas migration and having Dual Seal Element Adapter installed on Rotary Control Device (RCD). Based on the above circumstances, prior to drill Suban-X in 2021, the decision was made to drill Suban-X well with MPD without downhole valve installed. The mitigation to overcome gas migration and suppress the gas was by preparing sufficient water from water pond at wellsite and establishing a water network to keep filling the water pond. As a result, the well was successfully drilled to TD safely without any issues. The innovation to eliminate the utilization of downhole valve provides cost-reduction for material and drilling time savings. This innovation was first implemented in Corridor Block and is currently being used as a basic template for future drilling campaigns.