ABSTRACT

High-resolution borehole images are pivotal in delineating the depositional and diagenetic intricacies within Brazil's presalt carbonate reservoirs, which is essential for fluid flow characterization. These images, acquired through both logging-while-drilling (LWD) and wireline technologies, surpass conventional logs in resolution, aiding in comprehensible formation evaluation, drilling optimization, and completion design. Historically, wireline technologies were favored for their high-resolution capabilities, primarily due to the technical hurdles associated with embedding high-definition sensors within LWD tools for effective imaging under the challenging conditions while drilling.

Petrobras has recently incorporated two state-of-the-art LWD imaging systems in its offshore operations of Brazil. One system is a laterolog-type system that provides high-definition resistivity images for water-based muds. The other provides high-resolution acoustic images for any mud type and resistivity images for nonconductive (synthetic- or oil-based) muds, thereby bridging the previous gap with wireline technologies. A novel feature-based compression algorithm facilitates real-time image transmission to manage the bandwidth limitations of mud-pulse telemetry.

Deepwater operations present unique challenges, especially with heave-induced depth measurement inaccuracies during LWD imaging. Advanced heave-filtering workflows were developed to maintain image data integrity and obtain reliable geological, geomechanical, and petrophysical features representation. This paper highlights examples based on real cases from presalt carbonate reservoirs, displaying the initial application and learning curve of these LWD imaging technologies, marking a significant advancement in offshore reservoir characterization. The integration of these technologies enhances operational efficiency and contributes significantly to the ongoing evolution of drilling technologies for complex geological settings like Brazil's presalt formations.

INTRODUCTION

Understanding the controlling factors of fluid dynamics in Brazil's presalt carbonate reservoirs is essential due to its significant influence on hydrocarbon production performance. These characteristics, such as facies, fractures, vugs, and caves, stem from both depositional and diagenetic processes. The deployment of high-definition borehole imagery substantially augments our comprehension of depositional environments, offering finer resolution than other petrophysical measurement techniques, thereby facilitating the identification of connections among various facies and their internal structures. The integration of acoustic and resistivity imaging with additional borehole data optimizes drilling activities and supports advanced formation evaluation, reservoir characterization, and completion planning.

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