Abstract
This paper outlines the main challenges and achievements in well engineering experienced during the development of the Mero oil field, located in the Libra block of the Santos Basin Pre-Salt offshore area in Brazil. With an ambitious project including more than 60 development wells, the Mero campaign is underway with several wells already drilled and completed in an ultra-deepwater environment. The plan includes wells up to 6,000 m deep, crossing formations with considerable geological complexity and heterogeneity, and a reservoir with high silica content, making drilling particularly difficult. Moreover, the use of intelligent well completion (IWC) is a mandatory feature in the project, entailing a more elaborate completion scope. Injector and producer wells have different requirements in terms of zone selectivity—i.e., 2 and 3 zones respectively—, which unfold into different completion configurations for each.
The challenges encountered prompted the project team to work on continuous improvement and develop new engineering techniques and equipment. This made Mero a pioneer in the deployment of groundbreaking solutions. The implementation of open hole IWC configurations was key to improve operational performance as it allowed downsizing bit and casing diameters, besides simplifying the scope by eliminating one casing run and cementing. In the case of 4-phase wells, the conversion to open hole configuration allowed the construction of slender wells which dramatically improved performance especially in THD, resulting in a 38% reduction in mean drilling time when compared to the cased hole equivalent. For 5-phase wells, the scope simplification also proved beneficial, yielding a reduction of 21% in mean drilling time. Initially, open hole IWC was restricted to 2-zone selectivity, namely the "PACI 2z" configuration, so it was only applicable to Mero injector wells. For this reason, Mero producer wells had been originally designed with cased hole configuration. However, later the "PACI 3z" configuration was developed, which is an open hole IWC suitable for 3-zone selectivity, becoming feasible for Mero producer wells. Mero was pioneer in deploying PACI 3z and the installation was considered successful. Besides the numerous benefits, the PACI 3z configuration also presents potential risks, which must be studied and managed. Another significant innovation during the Mero campaign was the inaugural use of a Downhole Disconnection System (DDS) device, which was successfully installed in a single trip. The DDS is advantageous because it enables one-trip IWC to be run in severe fluid loss scenarios and allows reestablishment of IWC functionalities after an eventual heavy workover intervention. Finally, by analyzing the yearly evolution of mean operation duration in Mero, for both drilling and completion, a consistent improvement in performance can be observed, reflecting the project learning curve.
