Managing Lost Circulation in Highly Fractured, Vugular Formations: Engineering the LCM Design and Application

Managing severe to total lost circulation can present major challenges 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 for curing severe to total losses, such as those encountered in highly fractured formations. Controlling severe to total lost circulation in naturally fractured/vugular formations has always been challenging, particularly in carbonate formations across the Middle East. In such situations, conventional particulate LCMs may not be effective. This paper presents a strategy and discussion for three types of contingency particulate LCMs that can be efficiently applied on location and have been shown to reduce drilling nonproductive time (NPT) before resorting to more difficult and time-consuming options, such as gunks/cement. The design of the innovative LCMs is based on the concept of a multimodal (MM) particle-size distribution (PSD) that can plug a range of fracture sizes. This paper discusses a strategy for applying three types of LCMs [engineered composite solutions (ECS) or one-sack solutions] that may potentially cure severe to total losses in upper/intermediate sections and in reservoirs (where acid solubility is desired). They perform efficiently compared to solutions that require mixing 6 to 10 components and require less inventory on the rig. The greatest advantage is that experimental variation of various component types and amounts has been previously tested in the laboratory before selecting the optimum formulation. In laboratory-based tests, each MM LCM has efficiently sealed 3,000 microns slotted discs. When they fail to perform on larger slotted discs (more than 3,000 microns and up to 9,800 microns in one case), supplemental materials have been defined (i.e., swelling polymer and/or reticulated foam) to increase the plugging efficiency for worst-case applications. ECS-1 is a MM, tough LCM that is applicable for severe losses in upper/intermediate holes where acid solubility is not necessary. Successful field applications in highly fractured carbonate formations in the Middle East are presented using the tough LCM on its own and in combination with a swelling polymer and a high aspect ratio fiber to cure total losses. ECS-2, a high fluid-loss squeeze LCM, can be used where ECS-1 (even with supplements) fails and in applications where acid solubility is not necessary. The uniqueness of this LCM is fine-sized reticulated foam in the sack. This paper presents successful field applications for the combinations of this high fluid loss squeeze LCM supplemented with larger reticulated foam. ECS-3 is a MM, acid-soluble LCM designed to perform similarly to ECS-1 but in a reservoir where acid solubility is desired. The three ECS strategies, along with the supplemental LCMs, might provide more technically efficient options for managing severe to total losses in naturally fractured/vugular formations. The benefits of these solutions include reduced time and reduced NPT through the elimination of expensive and time-consuming trial-and-error applications on the rig.