Using Shape Memory Effect to Develop New Lost Circulation Materials for Sealing Large Fractures

Lost circulation is an uncontrolled flow of the drilling mud loss into a formation, here we are specifically interested in the lost occur through natural fractures. Such events should be prohibited in the field to minimize downtime and maximize the overall rate of penetration (ROP) as much as possible. One common method to mitigate lost circulation is the addition of lost circulation materials (LCMs) to the drilling mud to seal off fractures. Although there is a variety of LCMs in the market, there is still a need for LCMs to seal large width fractures (>5mm). Conventional LCMs can seal fractures with widths up to 5mm, while fracture widths could be much larger, particularly, in crystalline rocks drilled for geothermal energy. In this study, we use the shape memory effect of special polymers to develop LCMs which are thermo-mechanically programmed to be compacted enough for circulation with the mud and then unfold to their large permanent shapes after exposure to the high temperature at the bottomhole. Our thermomechanical programming methods include different types of loading, folding, twisting, and rolling to produce LCMs at small temporary shapes. Temporary shapes consist of disc-, spring-, zigzag-, spiral-, spider-, ladder-, and spindle-shaped configurations. These LCM materials are developed in three different categories: granular particles, one-dimensional (1D) or fibrous members, and two-dimensional (2D) or net elements. Results obtained from permeability plugging apparatus (PPA) tests confirm that the three-dimensional (3D) structure formed by using appropriate mixtures of granular, 1D, and 2D LCMs can seal fractures with at least 12mm width.