Deepwater MPD Operation and Design Method

Abstract

Abstract INPEX Offshore North West Sabah, LTD. has committed to drill two deepwater exploration wells in water depth upto greater than 1,000m offshore Sabah in East Malaysia. The typical deepwater wells, due to narrow drilling window between pore pressure and fracture gradient, require multiple CSG strings to reach total depth. Because of the uncertainty in pore pressure and fracture gradient prediction, which causes pressure-related well control problems, the initial CSG design with conventional method was conservative and highly costly design. Managed Pressure Drilling (MPD) with Constant Bottom Hole Pressure (CBHP) mode enables the development of an adaptive well design and safe operation by providing the following key points: Improved Kick ToleranceEarly Kick Detection by Coriolis Meter can reduce influx volume. Once MPD system detects the influx in "auto mode", the system automatically increases back-pressure to stop the flow while drilling. Typical influx in MPD mode is less than 3 bbls.Improved Safety and Well ControlIt mitigates the risk of exceeding MAASP with MPD because of smaller influx. Also it can enhance ability to safely circulate out gas in the riser.ECD ManagementIt enables to maintain the constant bottom hole pressure during drilling and connection. Adjusting MPD choke can manage the drilling safety margin. MPD application with the adaptive CSG design will most likely eliminate at least one CSG, and has potential saving of two CSG strings, which represents significant cost saving. The method introduced here is applicable to any deepwater well which has narrow drilling window. MPD application with Below Tension Ring RCD (Rotating Control Device) on 6th generation dynamic positioning rig can develop real time CSG setting depth optimization with the management of bottom hole pressure in each hole section.