Yu Xia

Aiming at the problems of low permeability, strong heterogeneity, high salinity, poor injectivity of the target reservoir, and the inability of traditional water flooding to effectively improve the oil recovery rate, a low interfacial tension and salt-resistant nano-scale particle-stabilized foam flooding system (LITF-NSF) was developed to improve the recovery rate of low-permeability oil reservoirs. Through core dynamic plugging and injectivity experiments, single/dual-tube core displacement experiments, and static imbibition oil displacement experiments, the injectivity, plugging effect, imbibition effect, oil displacement mechanism, and optimal injection parameters of the LITF-NSF foam flooding system were studied from three aspects: injection pressure, slug volume, and gas–liquid ratio. The LITF-NSF foam flooding system has good injectivity in the target reservoir, with a resistance coefficient ranging from 1.086 to 15.468; the optimal injection parameters are a constant pressure difference of 5 MPa, a gas–liquid slug volume of 0.3 PV, and a gas–liquid ratio of 2:1. Under these optimal injection parameters, the subsequent water flooding recovery rate can be increased by 29.77%; it can produce a good plugging effect on the high-permeability reservoirs of the target reservoir with a permeability difference of less than 50, and can increase the comprehensive recovery rate of heterogeneous oil reservoirs by more than 10%; the static imbibition recovery rate is 4.38% higher than that of pure water without surfactant, and has a certain permeability-enhancing oil displacement effect. The LITF-NSF foam flooding system has good adaptability to the target reservoir environment and stable foam performance, which can effectively improve the subsequent water flooding recovery rate and has a good application prospect in chemical flooding for improving the recovery rate of low-permeability oil reservoirs.

Severe reservoir heterogeneity in offshore oilfields often leads to dominant flow channels, high water cut, and low sweep efficiency during long-term water flooding. In this study, an in situ self-assembled composite foam system combining soft polymer particles with a low-interfacial-tension foaming agent was developed for profile control and enhanced oil recovery (EOR) in offshore heterogeneous reservoirs. The self-assembly characteristics and physicochemical properties of different particle systems were evaluated to optimize the composite foam structure. Static and dynamic experiments were conducted to assess foam stability, plugging performance, injectivity behavior, and oil displacement efficiency. Results show that the optimized composite foam undergoes in situ self-assembly under reservoir conditions, forming a stable particle–foam structure that enhances selective plugging and mobility control. Core flooding experiments demonstrate that the system increases oil recovery by up to 27.2% across a wide permeability range. Field application further confirms its effectiveness in regulating interlayer water absorption, stabilizing injection pressure, and reducing water cut. These results indicate that the proposed in situ self-assembled composite foam is a promising technique for integrated profile control and enhanced oil recovery in offshore heterogeneous reservoirs.

A quantity of recoverable barite exists in high-density waste drilling fluid. Based on the inefficiencies and complexities of existing recycling methods, a novel pre-treatment approach which includes clean-breaking, high-speed washing, ultrasonic dispersion, and microwave heating and a new depressant (Gellan Gum) was proposed. The floatability, separation efficiency and mechanism were discussed by SEM, adsorption capacity, zeta potential measurements and contact angle tests. The results of reverse flotation experiments results indicated that secondary water washing proves highly effective in enriching a significant quantity of barite solid phase. Subsequent microwave-ultrasonic and flotation can obtain barite of high quality with recovery and density reaching 81.5% and 4.238 g/cm³, respectively. It can be utilized directly in the preparation of drilling fluid. Mechanism studies shown that the per-treatments substantially enhances the barite grade while effectively eliminating low-density solid phases adhering to the barite surface, thus exposing additional contact points between the constituents so as to improve flotation separation. This new recovery scheme has environmental advantages and great reference value for the separation of barite within high-density waste drilling fluids.