Lost circulation is one of the major issues that lead to unwanted non-productive time (NPT) while drilling with a narrow mud weight window and it requires engineered solutions to address the problem. In several instances in the past, wellbore strengthening was achieved by treating the drilling fluid with lost circulation material (LCM), utilizing Stress Caging or Wellbore Strengthening theory. Small fractures were propped and sealed with a proper size distribution of particles that isolates the fracture tip from fluid pressure and controls the fracture propagation, effectively increasing the near wellbore hoop stress.Laboratory data and field experience indicate limited success may occur if a single material such as sized calcium carbonate is used alone for wellbore strengthening. This is possibly due to size reduction that may occur while drilling or due to fracture closure stresses (FCS) acting on the particles. However, using calcium carbonate in conjunction with resilient graphitic carbon (RGC) material has shown to be effective in increasing the formation integrity.The effect of mechanical properties of LCMs on wellbore strengthening has been investigated using compression/crush tests at different confining pressures simulating a wide range of FCS. Crush test demonstrated compaction and significant crushing of the ground marble and ground nut shells at high confining pressure (~ 5000 Psi). Considerable improvement in the crushing resistance and resiliency of these materials was observed with small additions of RGC. Knowledge of deformation and failure behavior of different LCM materials may result in better design. In this paper recommendations are made on different combinations of LCM that may be used more effectively to provide wellbore strengthening.

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High resiliency graphitic carbon lost circulation material (LCM) is one of several graphitic materials that achieve varied success. Effectively controlling loss of circulation (LC) is more than just selecting LCM and requires an engineered approach. Particulate LCM like ground marble, graphitic carbon and cellulosic fibres have been widely used but careful consideration should be given to how these materials are combined based on fracture types. Induced fractures created when the equivalent circulating density (ECD) exceeds the formation fracture gradient or during wellbore strengthening applications, could be "pressure-sensitive" as reported in fracture closure studies (Dupriest 2005). Resilient graphitic carbon (RGC) has many unique properties (Whitfill 2003) that can be exploited in lost circulation scenarios.Laboratory methods developed to characterize the resiliency of different graphitic carbons are presented, and the lack of resiliency of other LCM is demonstrated. RGC also imparts resiliency to other LCM combinations (Kumar 2010). Resiliency associated with RGC can be enhanced in an LCM combination that exhibits a granular nature, rather than forming a solid plug. RGC also imparts crush resistance to other more brittle LCM and can help reduce attrition, thereby retaining particle size for effective wellbore strengthening, while also acting as a solid lubricant.RGC is manufactured in a proprietary two-stage furnace process that produces 99.9% carbon content. It is conductive material with no magnetic properties, so it does not interfere with logging tools (e.g., density and neutron) and other downhole equipment. RGC is suitable for use in reservoir sections because it is completely inert and may be combined with acid-soluble ground marble to allow flow back.The paper includes field and laboratory data that validate RGC characteristics related to resiliency, lubricity, resistance to attrition,and compatibility with downhole tools, making it a versatile material for most LCM combinations for LC control and wellbore strengthening applications.

Particulate lost circulation materials (LCM) that work for severe-to-total losses are difficult, if not impossible, to find. Solutions that are effective for lower loss rates do not perform well at higher loss rates. Many LCM formulations have been used to treat severe losses, but their design and use has been more trial and error based mostly upon successful case histories. This paper describes the development of a combination of materials that is used in conjunction with other Engineered, Composite Solutions (ECS) to further enhance their performance.A novel combination of swelling materials, retarder, and fibers with a large aspect ratio is proposed as an activator that can be deployed with ECS typically available on the rig. The activator was designed and tested under conditions that qualitatively resemble severe lost circulation scenarios (large fractures). A shale swell meter was modified to qualitatively compare the swelling behaviour of different materials under different temperatures and retarder concentrations. A polyacrylamide-based swelling material was found to be sensitive to both temperature and retarder concentration. A newly sourced, potentially reservoir-friendly swelling material was found to be sensitive to temperature only. The activator-ECS combinations were tested for plugging capability with Permeability Plugging Apparatus (PPA) test equipment using different size tapered slots. Data from these modified PPA tests were used to determine the best combination of activator and ECS for plugging a particular-sized fracture simulated by the tapered slot.Field applications of systems that led to this proposed approach are discussed along with laboratory data comparing the swelling behaviour of different materials as related to mixing and pumping times.

With increased drilling activity in deeper, harsher, and more-complex environments, controlling nonproductive time during drilling is critical to lowering the cost of well construction. Lost circulation (LC), one of the main contributors to nonproductive time, is a widely discussed topic drawing industry attention, as is evident from recent publications and forums/workshops on the topic. The literature on LC reveals several means of mitigation, ranging from the simple use of lost-circulation materials (LCMs) to the use of gunk/chemical sealants and methods for altering near-wellbore stresses (stress caging or wellbore strengthening). There is a subtle difference between LC and wellbore strengthening, and any research should help facilitate a better understanding of the two.Presented previously (Kumar et al. 2010;Savari et al. 2012) were novel insights into LCMs for wellbore-strengthening applications. Continuing the research effort, this paper discusses another approach for designing LCMs to withstand higher wellbore pressures within a fracture. A property of plug-breaking pressure (PBP) was determined for different LCM combinations by use of a permeability-plugging apparatus (PPA) with tapered slots. LCM combinations with differing mechanical properties behaved differently compared with PBP data. Particles, such as ground marble, alone were not able to plug the tapered slot, and hence the PBP was zero. By use of the previous work described by Savari et al. (2012), the addition of resilient graphitic carbon (RCG) helped with plugging the tapered slot, with a PBP of approximately 900 psi. Adding fibers to the LCM combination was also evaluated. Plugging did not improve when fibers were added only to one other type of particulate LCM. But, the combination of ground marble, RGC, and specific fibers was found to provide the most-efficient plugging, with the highest PBP of approximately 2,100 psi.This work confirms that all LCMs are not equal and that the LCM type plays a role in terms of both plugging and "toughness" to better withstand displacement pressures. It also validates that, most of the time, combinations of LCMs work more effectively compared with the use of only one type. The novel PBP data on different LCM combinations can provide a qualitative comparison of their ability to withstand displacement and/or failure pressures when designing LCM combinations in wellbore-strengthening applications.