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Foam has been widely used as a proven technology in enhanced oil recovery by improving the mobility of the injected gas. However, its further application has been retarded owing to the limited stability in high salinity, high temperature and crude oil conditions. Traditional agents for foam stabilization including surfactants, polymers are unable to stabilize foam for long term under harsh conditions. In this work, the nanogel particles with high viscoelasticity were synthesized to stabilize foam for more than one year through a free radical reaction method using α-starch, acrylamide, N,N′-methylene bisacrylamide, potassium persulfate. The diameter of nanogel particles was 30 nm. The stability of foam stabilized by nanogel particles was evaluated by using foam volume and T90 as indicators at temperature of 30–120 °C, salinity of 0–240 g/L and oil percentage of 0–50 wt%. Moreover, the rheological properties of foam were also measured to study the mechanisms of foam stability under different conditions. The results demonstrated that foam stabilized by nanogel particles exhibited excellent resistance to high salinity, high temperature and crude oil. Thus, the synthesized nanogel particles can be used as a potential candidate for stabilizing foam in enhanced oil recovery.

Formation of low permeable external filter cake during drilling and water injection has been widely reported in the literature. It may cause significant decrease in well index. The process is very sensitive to size distribution of injected particles. We propose a new mathematical model for cake formation with deep bed filtration for two-particle-size injection. The basic equations account for three stages: formation of cake from large particles with simultaneous deep bed filtration of small particles; small particle capture in the cake with formation of the internal cake inside the external cake; build-up of the uniform cake from the mixture of two-size particles. The analytical model is derived for three stages. Two regimes of the cake formation are identified, which correspond to the high and low concentrations of injected small particles. The laboratory coreflood with two-particle-size suspension injection with monitoring the rate and pressure drop along the core is performed. The matched mathematical model shows good agreement with the laboratory data.

Permeability decline during high rate flows has been widely reported for corefloods and for production wells. The phenomenon is attributed to mobilisation of fine particles at elevated velocities, their migration in porous space with the following straining in thin pores and attachment to pore walls. Sixteen sets of corefloods with piecewise constant rate have been performed under increasing flow rate. The particularities of this study are long injection periods, allowing estimating permeability stabilisation times, and pressure measurements in intermediate core points, permitting for evaluation of the permeability profile variation along the core. It was found out that the mobilised particles drift with speeds significantly lower than the carrier fluid velocity, resulting in long permeability stabilisation periods.