Drilling Statically Underbalanced Gas Well with Managed-Pressure Drilling to Target Depth Safely and Efficiently

摘要

Drilling a statically underbalanced well means that the hydrostatic head exerted by the fluid used for drilling is lower than the formation pressure. However, by utilizing Managed Pressure Drilling (MPD) equipment, such as a Rotating Control Device (RCD), an automated MPD choke manifold, and a downhole isolation valve (DIV), and employing MPD techniques, such as Constant Bottomhole Pressure (CBHP) and Pressurized Mud Cap Drilling PMCD), surface backpressure can be exerted during drilling and a dynamically overbalanced condition can be established during the operation, thereby preventing the constant flow of reservoir fluids to surface. The CBHP variant of MPD was initially deployed with statically underbalanced drilling fluid to minimize damage to the reservoir until severe circulation losses were encountered, once the high permeability areas being targeted for the big-bore gas wells were penetrated. Thereafter, the same drilling fluid was to be utilized to make the transition to another MPD variant, PMCD, faster and easier. PMCD was utilized in order to continue drilling the well to target depth without needing to restore circulation and pump lost circulation material (LCM) and cement, which will also impair the productivity of the gas reservoir. This paper focuses on how these combinations of MPD techniques were successfully utilized in order to drill high-rate gas wells in South Sumatra safely and efficiently. Details of how the system was safely and efficiently installed and subsequently deployed, as well as the set-up and procedures utilized will be elaborated. Further improvements to the system and to the operation are also discussed for future applications. Finally, the evolution of MPD methods used in drilling the gas reservoir is also described in relation to the changes that have occurred to the reservoir after it has already been put in production for a number of years.