Self-Degradable Lost-Circulation Material Cures Dynamic Losses in Highly Fractured Section

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 219656, “Successfully Curing Dynamic Losses in a Highly Fractured Reservoir Section by Using an Engineered Self-Degradable Lost-Circulation Material in a Field Trial in the Middle East,” by Mohammed Omer, Francisco E. Fragachan, SPE, and Samuel K. Strickland, SPE, Weatherford, et al. The paper has not been peer reviewed. _ Lost circulation of drilling fluids costs the oil and gas industry approximately $1 billion per year, with the Middle East and North Africa region accounting for most of such lost-circulation events. In this case study, a geomechanics-based approach is used to create bridging and sealing at the fracture aperture using a biparticle self-degradable lost-circulation-fluid system. The approach, which includes a lost-circulation material (LCM), successfully prevented dynamic losses in the reservoir section without damaging the formation, confirming the viability of the technology and material. Principle of Self-Degradable Multiparticle LCM Previous work has emphasized that particle-size distribution is a key factor in sealing fractures. A physics-based approach to jamming and sealing of natural fractures depending on the particle-size-distribution (PSD) approach has been used. This approach has been applied in stimulation applications, wherein the stimulated zones are plugged or sealed to divert the stimulation slurry to understimulated and nonstimulated regions. If an entire flock of sheep tries to pass through a small gate simultaneously, they will not succeed. Using this analogy, the gate is a fracture opening and the sheep are discrete particles. The size, number (concentration), and speed (flow rate) of the total (minimum required) sheep that cannot enter the gate can determine the jamming for a specific gate opening. The same principle is applied to compute the concentration, mass, and flow rate of the LCM PSD for sealing a specific fracture aperture. Once a jamming has occurred, it does not necessarily mean that the fluid is restricted; gaps still exist where pressure communication is present or fluid loss will occur. Jamming will provide a foundation for moving on to the next stage (i.e., sealing off the small opening). In the plugging stage, the remaining flow paths where pressure communication is present within the jammed structure created by the large particles are filled by smaller particles of a specific shape. This will create high pressure buildup that prevents the entry of drilling fluid, thereby sealing off the fractures completely. Thus, the successful curing of the losses in naturally fractured formations depends on both jamming and plugging. With regard to the mechanism of jamming and sealing using the featured biparticle system, the larger particles of specific shape, size, ratio, and flow rate form a bridge or a plug across the fracture aperture, and the smaller spherical particles seal the gaps in the bridge, providing an effective plugging of the existing porosity after bridging. Once the shape is determined, focus is placed on optimizing the particle ratio and carrier fluid. In the authors’ experience, this system has effectively blocked openings with typical differential pressure increases of 500–4,000 psi.