Preparation and characteristic experiments of intelligent lost circulation materials based on thermally shape memory polymer

Lost circulation in fractured formation is a worldwide problem in drilling engineering, with the characteristics of unclear crack opening, low plugging efficiency, and etc. The traditional bridging materials for treating lost circulation are sensitive to crack opening, and it is difficult for them to achieve effective adaptive bridging plugging. Based on the new development of the shape memory intelligent materials discipline, the paper develops thermally stimulated shape memory intelligent lost circulation materials (density:1.16 g/cm3)with different particle sizes using the basic principle of "thermal-mechanical deformation", and experimentally evaluates its molecular structure, glass transition temperature and shape memory performance using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimeter and the test method of folding-expanding shape memory. The particle expansion and mechanical properties under high temperature and high pressure conditions were also tested. Through the simulation experiment of long fracture plugging, this study explores the fracture-plugging mechanism. The results show that the glass transition temperature of the thermally stimulated shape memory plugging agent can be adjusted according to the temperature of leakage zone (72.86~102.35℃), with the shape fixed rate and recovery rate greater than 99%. Under high temperature and high pressure conditions (120℃/ 20 MPa), the growth rate of D90 particles is more than 40%. After activation, D90 particles have high compressive strength, and thus are beneficial to the adaptive bridging plugging in fractures. The small stimulated shape memory plugging agent have a flaky shape before activation, easy to enter the fracture. After reaching the activation temperature, it expands to become a cubic massive 3D structure, and can adaptively match the width of fractures in the leakage zone within a certain range, showing high plugging efficiency. Using a set of formula of plugging fluid, it can successfully plug 3-5 mm coexisting fractures with different opening, achieving temperature-sensitive, adaptive and high-efficiency plugging. © 2020, Editorial Office of ACTA PETROLEI SINICA. All right reserved.