PLA@BPU Core–Shell Temporary Plugging Agent for Deep Fractured Reservoirs

Abstract

It is essential to efficiently plug fractures to control drilling fluid loss during the drilling phase. Additionally, it is crucial to ensure that these plugs can be reliably released after well completion to restore production capacity. This study synthesizes PLA@BPU, with three types of polyurethane prepolymers modified by different blocking agents (BPU) serving as the outer shell and polylactic acid as the core. The blocking efficiency of BPU was analyzed using titration and Fourier transform infrared spectroscopy (FTIR). The deblocking temperature of BPU was explored using the step-heating test and differential scanning calorimetry. Experimental studies investigated coating performance, thermal stability, adhesive performance, degradation behavior, enhanced plugging effectiveness, and reservoir protection of PLA@PBPU and explored its mechanism of action. Experimental results showed that three types of blocked polyurethane (methylene-blocked polyurethane (MBPU), phenol-blocked polyurethane (PBPU), and alcohol-blocked polyurethane (ABPU)) were synthesized, with a blocking efficiency of over 99%. Their deblocking temperatures were 120 °C, 140 °C, and 180 °C, respectively. PLA@PBPU demonstrated good thermal stability, with a tolerance of 282.2 °C and a weight loss of just 8.7%. The adhesive strength between particles was 1.65 MPa, and with the carbonate fracture surface was 0.13 MPa. The degradation rate of the PLA@PBPU solidified product was only 6.49% after 12 h and reached 99.24% after 32 h at 140 °C. Pressure-bearing capacity of PLA@PBPU for fractured cores (w = 3–2 mm, w = 6–4 mm) exceeded 17 MPa. For a dual-fractured core (w = 1.5 mm), the plugging rate was 98.23%; after 16 h, the permeability recovery rate was only 12.24%, and after 44 h, it reached 97.23%. This study offers a new solution to the challenge of balancing drilling fluid loss control with reservoir protection.