Managed pressure drilling (MPD) technology is a widely accepted technology for wells with narrow pore- pressure/fracture-pressure (PP/FP) gradient window. Whilst MPD is often associated with high capital expenditures (CAPEX) that further erodes the project economics especially for marginal reserves, it does not limit its application since MPD technology can considerably reduce non-productive time (NPT). Most importantly, it is the key enabler to access the previously conventionally un-drillable reservoir target, generating significant revenues to the organization. As the plan new development well cannot be drilled conventionally by using overbalance mud, numerous dynamic drilling simulations were performed utilizing drilling engineering software to ascertain its drill- ability via constant bottomhole pressure (CBHP) MPD with statically underbalanced mud. As an input, detailed surface equipment specifications, i.e., surface MPD line up and well control equipment are important to ensure successful drilling simulations. Sensitivity analysis using surface back pressure and drilling mud density are performed to determine maximum drillable footage for each hole section. As proper cementing is paramount for well barrier, well drill-ability is further assessed with managed pressure cementing (MPC) simulation to ensure the well is operationally executable. This paper presents a case history on operations performed in-house well engineering design for a complex and marginal deepwater development field during front end stage with narrow PP/FP gradient window (less than 1ppg drillable mud window) and elaborate on extensive work done for MPD engineering planning procedures in designing a fit-for-purpose well design.

Limbayong field situated in Sabah, Malaysia is operated by PETRONAS Carigali and is the company's first deepwater operated asset owned and operated by PETRONAS. Limbayong is a flagship project and strategically aims to be the deepwater hub for East Malaysia, particularly Sabah. The first phase of development is to start in Q1 2023. One of the campaign objectives is to produce from the deepest reservoir. However, the recently updated geomechanics model shows that there is a need to drill through with an extremely narrow drilling margin window (less than 0.5 ppg) even at the surface section for some of its wells. Most of these deep wells are required to be drilled in highly deviated and in the direction of the minimum horizontal stress. This poses an increased risk of stuck pipe due to hole instability, differential sticking, and skin damage due to high overbalance pressures, which makes drilling these wells challenging and costly. A mechanical earth model is initially developed based on Limbayong offset. The model has gone through an evolution with the recent model being updated to better fit observation in sand locally and regionally in recent wells drilled. The new reconstruction model significantly reduces the drilling window gap, thus MPD (MANAGED PRESSURE DRILLING) is required to meet the well objective and minimize drilling risk. By developing and applying those models, it helps to determine the safe operating downhole pressure limits and to effectively assess the drilling risks associated with the planned wellbore orientation. By accurately determining the required bottomhole pressure to prevent wellbore stability problems, managed pressure drilling technology can be implemented to provide improved drilling hazard mitigation by enabling reduced overbalance pressures, constant bottomhole pressure, and faster reaction time by instantaneously adjusting downhole pressures. This work underscores the development and usage of the advanced multi-phase model to simulate gas influx transport and its effects on BHP (Bottom Hole Pressure) during MPD operations. DrillBench hydraulics modeling was performed to determine the mud weight requirements to be used with the MPD system. Using the lowest MW (Mud Weight) possible to maximize the drilling window and flexibility was implemented as part of scenario simulation. This paper presents a case study where a holistic approach, combining geomechanics and drilling technologies were employed to address the drilling challenges specific to unconventional and naturally fractured reservoirs. Ultimately, this approach helped to mitigate stuck pipe issues, while proposing an engineering-based methodology to reduce losses by using MPD, hence providing a roadmap to optimized drilling and mitigation of hazards with associated Non-Productive Time (NPT).