Evaluation of shape memory polyurethane as a drilling fluid lost circulation and fracture plugging material

Abstract

In a previous work, we developed shape memory polyurethane lost circulation materials (SMPU LCMs) programed to recover at wellbore temperature and plug fractures. Further testing and characterization of SMPU LCMs under various conditions and in the presence of different drilling fluid additives promote their field applicability. In this work, SMPU LCMs with 13/12/1, 18/17/1, and 25/24/1 M ratio of (hexamethylene diisocyanate/1,4 butanediol/polycaprolactone diol) were synthesized. Mechanical property testing indicated that SMPU13121 had the highest shape recovery (98.3%) and shape fixity (99%) and wellbore activation temperature of 59.1 °C. SMPU13121 was selected as the medium size SMPU LCMs to build the bridge. SMPU25241, with the highest Young's modulus (48 MPa), tensile strength (8.9 MPa) at 80 °C, and compression resistance (85.4 MPa), was selected as the fine SMPU LCMs to maximize the plug mechanical strength. A specifically designed particle permeability apparatus paired with a series of stainless-steel discs was utilized to investigate SMPU loss circulation attributes in cracked impermeable formation with varying fracture metrics, including fracture thickness and fracture wall angle. Different weighting materials and drilling fluid densities were employed. In straight slot discs, the bridging occurs largely near the fracture mouth and is independent of disc thickness, whereas in tapered discs, SMPU LCMs sealing pressure improved by 9% and 146% with increasing fracture depth, from 13.07 mm to 52.3 mm, and decreasing wall angle, from 3.5° to 1.15°. Furthermore, increasing drilling fluid density from 1442 kg m−3 to 1762 kg m−3 increases the fracture sealing pressure by 11%. Different weighting materials also increase the fracture sealing pressure, depending on the particle size distribution and the morphology of the weighting material. The barite-WBM had the highest sealing pressure at 8.97 MPa, while the limestone-WBM had the lowest sealing pressure at 8.05 MPa. Limestone larger particle size distribution and lack of particle size in the range 63 μm–100 μm may explain the limestone-WBM lower pressure sealing ability.