This study presents a study of nanoclay-surfactant-stabilized foam to improve the oil recovery of steam flooding in offshore heavy oil reservoirs. The foam stability and thermal resistance studies were first performed to investigate the influence of nanoclay on the stability and thermal resistance properties of the foam system. Then, the sandpack flooding tests were conducted for investigating the resistance factor and displacement abilities by nanoclay-surfactant-stabilized foam. The results showed that the nanoclay-surfactant-stabilized foam has excellent foaming ability and foam stability at 300 °C, which can be used in steam flooding for offshore heavy oil reservoirs. The resistance factor is greater than 30 at 300 °C when the gas–liquid ratio ranges from 1 to 3, which indicated that the nanoclay-surfactant-stabilized foam has good performance of thermal resistance and plugging effect. The heterogeneous sandpack flooding test showed that the nanoclay-surfactant-stabilized foam can effectively divert the steam into the low-permeability area and improve the sweep efficiency, thus improving heavy oil recovery of steam flooding. Therefore, the nanoclay-surfactant-stabilized foam flooding has a great potential for improving oil recovery of steam flooding in offshore heavy oil reservoirs.

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Cyclic steam stimulation is an effective thermal recovery method for heavy oil recovery. The key potential mechanism is the growth of the steam chamber after steam injection. Taking the LD5X heavy oil reservoir as an example, besides the interlayer developed in this area, the top water and bottom water distribute above and below the interlayer. These factors may have adverse effects on the development of the steam chamber, thus affecting the final heavy oil exploitation. In this work, our goal is to study the effects of interlayer permeability and well–interlayer distance on CSS performance (in the presence of top and bottom water). We developed a high-temperature-resistant interlayer. Based on the simulated interlayer, the field scale model was converted into a laboratory element model through the similarity criterion. In order to quantitatively evaluate the performance of steam stimulation, a thermal detector was used to measure the dynamic growth of the steam chamber and record the production data. The experimental results show that the self-made interlayer has high-temperature resistance, adjustable permeability, and little difference between the physical parameters and the target interlayer. During the cyclic steam stimulation process, the steam chamber presents two different stages in the presence of the top water area, namely the normal production stage and the top water discharge stage. The bottom water has little effect on the growth of the steam chamber. The small interlayer permeability, the increase in horizontal well–interlayer distance, and the existence of the interlayer will delay the top water leakage during steam stimulation. This study has reference significance for us to develop heavy oil resources with a top water barrier when implementing steam stimulation technology.

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Chemical-assisted steam flooding is a promising method for heavy oils. However, few researches have investigated the performance of nitrogen foam and gel-assisted steam flooding (NFG-A-SF) on offshore heavy oil reservoirs. In addition, the effects of operational parameters on the performance of NFG-A-SF are still unclear. In this study, a numerical simulation model was developed to simulate NFG-A-SF processes for offshore heavy oil reservoirs. Then, a comparison of NFG-A-SF and steam flooding was made to assess the feasibility of NFG-A-SF in a well group at Oilfield L, a typical offshore heavy reservoir of Bohai Bay, China. Finally, sensitivity analysis was conducted to investigate the effects of the chemical agent type, injection mode, injection timing, cycle number of gel and nitrogen foam, polymer concentration, crosslinking agent concentration, foaming agent concentration, and gas-liquid ratio on NFG-A-SF performance. The results showed that, compared with SF, the NFG-A-SF has better performance, which is a potential and effective method for offshore heavy oil reservoirs. The NFG-A-SF should be implemented as early as possible. During the NFG-A-SF processes, gel slugs should be injected alternately with nitrogen foam slugs, and the gel slugs should be injected first before nitrogen foam slugs. Considering the economic benefit, there are optimum cycle numbers of gel and nitrogen foam, gas-liquid ratio, concentrations of polymer, crosslinking agent, and foaming agent.