This paper presents a comprehensive laboratory and field study discussing development, formulation, and application of a new flat rheology drilling fluid system that meets the challenges faced when drilling in an ultradeepwater well environment. The use of this new flat rheology drilling fluid system for the first time in Asia-Pacific Region has created the potential to efficiently drill more challenging deepwater and ultra deepwater wells in offshore Myanmar, Malaysia, and other associated countries.

In a deepwater block situated on Myanmar's west coast, conventional synthetic-based drilling fluids (SBM) have been used to drill all the wells to date. During the planning phase of an ultradeepwater well with a water depth of 2,300 m, it was found that the equivalent circulating density (ECD) with a narrow pore pressure and fracture gradient would have increased downhole complications leading to non-productive time (NPT). The main concern was not being able to reach total depth (TD) or successfully setting casing on bottom with the original well design, requiring implementation of a contingency casing and pushing the operational cost over authority of expenditure (AFE). To overcome the challenges, a new flat rheology drilling fluid system was introduced based on ECD challenges and rheology requirements. The initial study of modelled hydraulics showed a significant ECD reduction using a flat rheology drilling fluid system.

The first round of laboratory tests exhibited promising results of flat rheology across all temperature ranges and after iterating numerous formulations developed with local seed mud were narrowed down to two final formulations of 1.08 sg and 1.17 sg. The formulation was field trialed with some slight adjustment in chemical concentrations to meet specific field mud properties. The well was drilled successfully with no major variation in ECD or issues related to the large temperature range. Implementing this customized solution combined with precise strategy led to successful results in efficiently completing one of the most challenging wells of the campaign.

The paper presents a comprehensive study of the challenges formulating and implementing a new flat rheology drilling fluid system. Additionally, a detailed study on ECD challenges when drilling an ultradeepwater well is also done. The paper also discusses the comprehensive pit management program and required treatment plan for drilling. Finally, the paper aims to compare the existing results with previous drilling techniques, which will assist operators with the future advances in similar fields.

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