Chemical EOR (CEOR) methods such as polymer-surfactant flooding are used to reduce oil trapping and mobilize remaining oil. This trapping is mainly a resultant of capillary trapping associated with waterflooding. Hence, it is believed that earlier implementation of CEOR post water-flooding will result in higher oil recovery, as the impact of capillary trapping will be less prominent in this case.

One of the main challenges associated with CEOR flooding is the high implementation cost. Earlier implementation results in higher cost, hence defining the optimum implementation time necessities evaluating both ultimate recovery and Net Present Value (NPV). This study investigates the effect of post-waterflood implementation time of surfactant-polymer flooding on ultimate recovery and (NPV) - given this capillary trapping – in order to determine the optimal implementation time while maximizing the dual objectives of NPV and ultimate recovery.

CEOR has been identified as an effective EOR method which is usually implemented in tertiary mode, where field development has reached a mature level. At this stage, the efficiency of waterflooding in terms of mobilizing remaining oil declines due to capillary trapping. Although this EOR process have been implemented in tertiary mode, experimental results of earlier implementation have shown more desirable effect on recovery because capillary trapping is less prominent.

This study investigates impact of post-waterflood implementation time of surfactant-polymer flooding on ultimate recovery and (NPV) given this capillary trapping. A series of numerical experiments were conducted to test this effect while accounting for operating expenses associated with both flooding options. Capillary pressure curves for the waterflood case and the chemical flood case were added to incorporate capillary trapping effects. Then, the chemical-flood implementation time was varied to evaluate its impact on the ultimate oil recovery and NPV These experiments were performed on 2 stylized reservoir models: the PUNQ-S3 and SPE10 reservoir models.

In a previous work, we have only covered the static properties. A pronounced impact was seen on the NPV however no drastic changes were recorded on the ultimate recovery. In this study, we implement a robust model accounting for all dynamic properties associated with varying the implementation time of CEOR flooding including effects on the relative permeability.

In general, the sooner chemical EOR is implemented the higher the ultimate recovery of the process. Also, results show that the optimum implementation time – based on NPV values - is function of reservoir heterogeneity, as the more heterogeneous model has earlier optimum implementation time.


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