Abstract

With the advantages of high sweep efficiency and displacement efficiency, alkaline-surfactant-polymer (ASP) flooding can greatly improve the oil recovery by 20%. The microscopic displacement mechanisms have been reported in detail, however, the macroscopic 3D fluid flow characteristics still lack enough research. This paper is aimed to study the macroscopic flow dynamics in ASP and further clarify the distinctions of remaining oil saturation between waterflooding and chemical flooding.

The flow dynamics were examined at both laboratory and numerical scale. A sandpack physical model was designed to simulate the vertical heterogeneous reservoir. To analyze the pressure distribution during the ASP flooding, the model was equipped with 25 pressure transducers. Then we built the corresponding numerical model to simulate the ASP process. Basic experiments data were used for history match and chemical parameters. In the simulation, we investigated the base case (pure waterflooding) and seven chemical flooding scenarios (alkali, surfactant, polymer, alkali-surfactant, alkali-polymer, surfactant-polymer, alkali-surfactant-polymer flooding, respectively).

"Enhanced oil saturation (EOS)" is defined by subtracting each chemical flooding from waterflooding case. The distribution maps/profiles were generated for comparison in eight cases. Viewed from the x-y areal plane, in the cases added with polymer, the injected chemicals from main streamline were observed to gradually spread to the two sides apart to displace the remaining oil. Besides, chemicals were diverted into lower permeability at vertical section. Based on the saturation profile presented in each chemical flooding scenarios, we classified the enhanced oil area into 4 subzones: A-zone, S-zone, P-zone and ASP-zone. This division characterized both individual and synergistic effects in alkali, surfactant, and polymer. Sensitivity analysis was conducted to compare the influence of alkali, surfactant, and polymer with different concentrations on the area where oil was extracted. Results show that: (1) as the polymer concentration grew higher, all the sub-zones displayed increasing tendency, but the impact would diminish if the concentration exceeded 1500 mg/L; (2) a relatively rich surfactant-bearing solution helped expand P-zone, and the ASP-zone is also benefited; (3) an optimal alkali concentration is advised to be 1% ~1.5%.

We establish a comprehensive characterization of the fluid flow dynamics by performing physical experiments and numerical simulation. The novelty of the paper is the inspection on the location where extra oil is driven by the function of each component. The synergy in ASP is recognized by pressure and saturation distribution. The study provides a better understanding of macroscopic flow mechanisms in chemical flooding projects.

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