DEVELOPMENT OF PLUGGING COMPOSITIONS BASED ON POLYACRYLAMIDE HYDROGELS WITH DISPERSED AND FIBRE FILLERS

Development and operation of wells at oil and gas fields are often accompanied by unexpected complications related to drilling mud loss and breakthrough of gas and fluids through reservoir fractures, which requires repair and insulation operations (RIO) to be performed with adequate quality. The ways to improve the efficiency of repair and insulation operations in oil and gas wells with the use of gel-forming plugging materials are considered in the work. The use of various hydrophilic and hydrophobic dispersed and fibrous fillers in hydrogels based on polyacrylamide and complex organic crosslinker is proposed in order to improve their rheological properties and increase the blocking ability. Such organic-inorganic composites show a variety of rheological properties, which makes it possible to select the necessary hydrogel compositions for certain RIO. The results of rheological (oscillation) and filtration studies, as well as field tests of the compositions, are presented. Chrysotile, carbon black, hydrophilic nanosilica, and mechanically activated wood flour, rice husk, hydrolysed lignin were used as dispersed fillers in oscillation studies. Polypropylene fibres, basalt fibres and carbon fibres were considered as fibre fillers. The values of elastic modulus (G′) and viscosity modulus (G″), crossover points and linear viscoelastic regions for each composition were determined from the results of oscillation studies. An increase in the modulus of elasticity up to 48 % (G′ = 53.3 Pa) was achieved with the addition of carbon black and up to 50 % (G′ = 54.2 Pa) for the composition with chrysotile and carbon fibre, compared to the base hydrogel without fillers (G′ = 36.1 Pa). The addition of hydrophilic nanosilica allowed an increase in the yield strength (crossover point) by more than 300 % (to 210.4 Pa). Filtration studies were performed on the ideal fracture model with different opening (50, 100, 650 μm) using natural core samples. It has been established that during water filtration the hydrogel with chrysotile and polypropylene fibre additives has a higher residual resistance factor (RRF = 167) in the fracture with 100 μm opening than the base hydrogel (RRF = 136) in the 50 μm fracture. When blocking a gas-saturated model of an ideal fracture, the maximum RRF was 2677. Field tests of the composition with dispersed and fibre fillers for elimination of catastrophic drilling mud circulation loss and RIO were successful.