Managing severe to total lost circulation can be very challenging in naturally fractured formations. Particulate lost circulation materials (LCMs) have been used to manage lost circulation for many years; however, current LCMs are not efficient in terms of their size and application methods when it comes to curing severe to total losses, such as highly fractured formations. In the present paper, preventive (proactive) and remedial (reactive) operational strategies will be discussed. In addition to the operational strategy, this paper will also present novel additives in the form of engineered composite LCM solutions (ECS) with multi-modal particle-size distribution (PSD), which were successfully used to manage severe-to-total-loss situations in naturally fractured carbonate formations. The multi-modal PSD will help manage any uncertainties in fracture sizes, and the presence of larger particles will also aid in plugging large fractures. Case studies will be presented for applications in the mid-continental USA, Middle East, and offshore East Africa. Preventive strategies are recommended to reduce the potential for lost circulation (LC). It is recommended that LC management be considered in the wellbore planning/design phase and that all engineering analyses be performed prior to the start of drilling the well. It is very important to have remedial strategies in place if the preventive plan does not work. This includes putting loss contingency plans in place should unexpected loss events occur. Examples will be discussed as to how previous knowledge and lessons learned can play a critical role in developing contingency engineered solutions to effectively cure losses. When managing severe-to-total losses in highly fractured formations, particulates alone may not be effective. The combination of a large multi-modal PSD LCM, a swellable component, and chopped synthetic fibers were proposed as a solution for dealing with such extreme losses. While drilling highly fractured formations, this combination was applied after all conventional LCM applications failed. In most cases, the combination was pumped open-ended, and losses were totally cured so that circulation could be re-established. To conserve rig time, the use of a treating sub is recommended as part of the BHA for handling high concentrations of large PSD LCMs for curing severe losses. The combination of operational strategies (LCM applications) and novel LCM solutions for curing severe-to-total losses in naturally fractured formations are the technology improvements presented in this paper.
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