Experimental Study of the Swelling and Rheological Properties of a High-Strength Preformed Particle Gel Lost Circulation Material

Abstract

Preformed particulate gel (PPG) has emerged as a widely utilized lost circulation material in deep oil and gas drilling operations. The objective of our study was to devise a high-strength preformed particle gel (HSPPG) specifically designed to address drilling fluid loss in high-temperature fractured formations. To achieve this, a comprehensive set of laboratory experiments was conducted to assess the swelling and rheological properties of HSPPG under various conditions, and these investigations aimed to provide deeper insights into the pressure-bearing mechanism exhibited by HSPPG. The synthesis of HSPPG involved the copolymerization of acrylamide (AM) and N-hydroxymethacrylamide (NMA) molecular chains, catalyzed by organic peroxides, to form the primary network. Additionally, to enhance its temperature resistance, urea-formaldehyde (UF) resin, known for its superior thermal stability, was incorporated into the secondary network. This unique combination of primary and secondary networks imparted remarkable thermal endurance and structural stability to the resulting HSPPG. The swelling and rheological experiments revealed that HSPPG, with a particle size of 1000 µm, exhibited an equilibrium swelling rate (SR) value of 30.55 and a storage modulus (G’) of 1050 Pa at 120℃. These findings attested to its excellent temperature resistance and structural stability. Furthermore, when subjected to a sodium chloride solution at a temperature of 120℃ and a concentration of 25.0%, HSPPG achieved equilibrium swelling with an SR value of 24.93 and a G’ of approximately 7000 Pa. This significant increase in structural strength was attributed to charge shielding within the highly concentrated brine environment. In the plugging experiments, a wedge-shaped slit with an inlet of 3 mm and an outlet of 1 mm was successfully blocked using a concentration of 4% of HSPPG with a particle size of 1000 μm. The blocking strength achieved was 8.06 MPa. The results of these experiments, as well as the observed filling and plugging state of HSPPG in steel fractured cores, indicated that HSPPG possesses the properties of water absorption, swelling, and extrusion filling. These attributes facilitate the effective formation of a dense blocking layer within the fracture space, exhibiting excellent pressure-bearing capacity. In conclusion, the HSPPG developed in this study represents an advanced swellable granular plugging agent with excellent swelling capacity and structural strength at high temperatures. It offers an ideal solution to mitigate drilling fluid loss from fractured formations under high-temperature and high-salinity conditions.