Abstract
The Saertu Oilfield of Daqing in northeast China has entered ultrahigh water-cut stage of development. Numerical simulation is applied in this paper to study characteristics of microscopic fluid velocity and flow pressures variation in the core pores in the Beier Area of Saertu Oilfield. The relationship between the remaining oil distribution and microscopic flow characteristics of fluid in the pores has been analyzed. Study results show that, in the reservoir with stronger heterogeneity of grain size and throat (corresponding to high coordinate number), high flow velocities tend to occur in relatively wider pore throats with great differentiation of flow velocities. The dominant passages are developed in high capacity channel, the detour flows are created in large porous channels, and the isolated islands are formed in small porous channels. The flow velocity declines slowly with long duration of high pressure. Few pores are swept by injected fluids with low sweep efficiency. The microscopic remaining oil is mainly distributed in cluster state. The content of remaining oil is higher with lower oil displacement efficiency. By contrast, in the reservoir with weaker heterogeneity of grain size and throat (corresponding to low coordinate number), high flow velocities also develop in relatively narrower pore throats with little differentiation of flow velocities. The development of detour flows is weaker in large porous channels. The flow velocity declines quickly with a short duration of high pressure. More pores are swept by fluids with high sweep efficiency. The remaining oil is mainly distributed in state of thin film on pore surface. The content of remaining oil is lower with higher oil displacement efficiency.
Highlights
The Saertu Oilfield of Daqing has entered ultrahigh water-cut stage of development
Previous studies indicated that the distribution of microscopic remaining oil in reservoirs was associated with pore structure and fluid
The Beier Area of Saertu Oilfield is located in the northern part of Daqing Placanticline from the Songliao Basin (Figure 1) with a gentle structure and formation dip angle of about 3∘ [23]
Summary
The Saertu Oilfield of Daqing has entered ultrahigh water-cut stage of development. When the comprehensive water cut of an oilfield reaches an ultrahigh stage, macroscopic study cannot well solve the problems of remaining oil distribution, so a more detailed investigation in a pore scale is necessary [10–14]. Previous studies indicated that the distribution of microscopic remaining oil in reservoirs was associated with pore structure and fluid. A combined study on distribution characteristics of the microscopic remaining oil in reservoirs on a comprehensive basis of pore structures, heterogeneity, and microscopic flow of fluid in pores is significant to make reasonable development plans during the ultrahigh water-cut stage. The geological models and mathematical models of a pore scale are established to simulate the fluid velocity and flow pressure distribution in pores with different pore structures, with aims of understanding the relationship between the velocity field of fluid in pores and distribution of microscopic remaining oil and of analyzing the oil displacement efficiency as well
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