Abstract
In this paper, viscosity reducer of viscosity-reducing ability and foaming ability on the recovery efficiency in N2 huff-n-puff were studied. The optimal 4# viscosity reducer was selected by evaluating the ability of viscosity-reducing, emulsion stability, interfacial performance and foaming. The huff-n-puff experiments of single sandpack and dual sandpack were carried out under the reservoir conditions. The results showed that, the viscosity reduction rate of 4# viscosity reducer was more than 90% at 50 ~ 90℃, and it could form a stable oil/water emulsion when applied to heavy oil. Under the action of 4# viscosity reducer, the interfacial tension between oil and water decreased to 0.41 IFT/mN·m-1 and 0.19 IFT/mN·m-1 at 50℃ and 80℃, respectively. In the single sandpack huff-n-puff experiment, the 4# viscosity reducer could inhibit N2 bubbles coalesced in large channels and improve the mobility of heavy oil. Compared with N2 huff-n-puff, the recovery rate of N2 huff-n-puff assisted by 4# increased by 8.53%. In the dual sandpack huff-n-puff experiment, the N2 was inhibited to flow from the low permeability sandpack to the high permeability sandpack by 4# viscosity reducer, and the gas production of the low permeability sandpack increased by 284.71%. Under the combined action of viscosification and plugging, the total oil production of the sandpack increased by 7.88%. Therefore, N2 huff-n-puff assisted by viscosity reducer has a significant effect on enhancing oil recovery in heavy oil reservoirs.
Highlights
With the development of economy, the demand for oil resources is increasing
The 48 ml viscosity reducer and 112 ml heavy oil were stirred for 3 min by magnetic stirrer at a constant speed (800 rpm); the emulsion was left to stand for 6 min
The 1% viscosity reducer solution and the heavy oil sample were placed into TX-500C rotating interfacial tension (IFT) apparatus at a constant speed of 5,000 rpm, and the oil–water IFT at 50 and 80°C was measured
Summary
With the development of economy, the demand for oil resources is increasing. In the world oil reserves, heavy oil reserves account for more than 70% (Yu, 2001; Zhang et al, 2010). The N2 huff-n-puff experiments were performed to investigate flow behaviors of different permeability levels and the effect of viscosity reducer on oil recovery. Viscosity Reduction Effect Evaluation Experiment Apparatus: DV2TLV digital viscometer (BROOKFIELD, United States, measure range: 1–6,000,000 cP), magnetic stirrer (XiangTian, China, speed range:
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