Borehole images play a crucial role in understanding the depositional environment and diagenetic processes that govern fluid flow in Brazil's presalt carbonate reservoirs. Acoustic and resistivity image logs offer superior resolution compared to the other types of measurements normally acquired for reservoir characterization using either logging-while-drilling (LWD) or wireline technologies. Advanced formation evaluation techniques can be employed to characterize the reservoir, optimize drilling operations, and design completion strategies by combining image logs with additional borehole data. Traditionally, the analysis relied on wireline conveyance technologies, primarily due to the challenges of integrating high-resolution sensors into logging-while-drilling tools capable of capturing detailed images in harsh drilling conditions.

Petrobras recently adopted two high-resolution LWD borehole imaging systems for Brazilian offshore operations. One of these systems offers high-resolution acoustic images suitable for all types of drilling mud, along with apparent resistivity images specifically designed for oil-based mud. The second technology deployed is a laterolog-type system that acquires borehole images with water-based mud. This implementation enables high-resolution borehole imaging while drilling for all mud types, closing a previous technical gap between LWD and wireline technologies. Both technologies use a unique feature-based data compression method to transmit the images in real time.

In deepwater operations, acquiring high-definition LWD images can be compromised by heave-induced errors in the depth measurement taken as a reference, currently provided by the rig. To address this, heave-filtering workflows are applied to preserve the integrity of subsurface features. Processing of the time-indexed data using this application yielded positive results, instilling confidence in the capabilities of these technologies.

Examples from five wells drilled in presalt carbonate reservoirs are used in this document to present and support the first experiences and learning curve using these LWD imaging technologies in Petrobras offshore operation to enhance reservoir characterization.

You can access this article if you purchase or spend a download.