Impact of Chemical Flood Mode on Oil Recovery in Fractured Carbonates

Alshehri, Amar J.; Kovscek, Anthony R.

doi:10.2118/172809-ms

Cited by 2 publications

References 22 publications

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Laboratory Investigations To Determine the Effect of Connate-Water Composition on Low-Salinity Waterflooding in Sandstone Reservoirs

Shehata

Nasr‐El‐Din

2016

SPE Reservoir Evaluation &Amp; Engineering

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Summary Most previous low-salinity-waterflooding studies focused on injection-brine salinity and composition. The question remains: How do the salinity and composition of the reservoir connate water (CW) affect the low-salinity-waterflooding performance? The main objectives of this work are to evaluate the potential of low-salinity waterflooding (LSW) on the performance of oil-recovery improvement by use of Buff Berea sandstone and Bandera sandstone cores; examine the effect of the salinity of the reservoir CW; investigate the role of the cation composition (Na+, Ca2+, and Mg2+) of the reservoir CW; and study the effect of temperature and pore-throat distribution on the performance of LSW. In this research, 11 spontaneous-imbibition (SI) experiments and six coreflood experiments were performed. Two sandstone types (Bandera and Buff Berea) with different mineralogy compositions were used. Furthermore, ζ-potential measurements were conducted for oil/brine interfaces to investigate the interaction between brine and crude oil interfaces. In addition, coreflood experiments were performed to validate the SI results and examine the effect of the CW-salinity variation. The reservoir-CW composition had a dominant influence on the oil-recovery rate. The changes in the cation composition of reservoir CW (Ca2+, Mg2+, and Na+) showed a measurable change in the oil-production trend. Reservoir cores saturated with CW containing divalent cations of Ca+2 and Mg+2 showed higher oil recovery than cores saturated with monovalent cations (Na+). The results demonstrate that the SI produced oil ranging from 38 to 69% of original oil in place (OOIP) for high-permeability Buff Berea cores (164–207.7 md), whereas the produced oil of the low-permeability Bandera cores (31.1–39.2 md) ranged from 20 to 51.5% of OOIP at 77 °F and 14.7 psia. In all cases, a measurable ion exchange was observed, whereas there was no significant change in the pH value of the imbibition brine during the experiments. The ion-exchange effect was more pronounced than the pH effect in the low-salinity-waterflooding performance for Buff Berea and Bandera sandstone. The total oil recovery increased from 51.9 to 58.9% OOIP when the divalent-cation (Ca+2 and Mg+2) concentration of the reservoir CW increased from 709 to 12,210 ppm for injected-brine salinity of 500 and 5,000 ppm, respectively. On the other hand, increasing the monovalent-cation (Na+) concentration from 610 to 54,400 ppm resulted in a slight increase in oil recovery (2.3% of OOIP).

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Laboratory Investigations To Determine the Effect of Connate-Water Composition on Low-Salinity Waterflooding in Sandstone Reservoirs

Shehata

Nasr‐El‐Din

2016

SPE Reservoir Evaluation &Amp; Engineering

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Impact of Chemical Flood Implementation Time on Ultimate Recovery and Net Present Value

2016

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During waterflooding processes, injected water disconnects oil droplets as it flows through pores/throats in the reservoir. These disconnections are a consequence of capillary effects hindering the mobilization of oil through pores/throats of the reservoir. Thus, mobilizing the remaining oil in place by any enhanced oil recovery (EOR) process becomes very challenging. Chemical flooding 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. Chemical EOR (CEOR) methods such as polymer-surfactant flooding are used to reduce this trapping and mobilize the remaining oil. Although most EOR processes have been implemented in tertiary mode, earlier implementation is more desirable, because capillary trapping is less prominent. This study investigates the impact of post-waterflood implementation time of surfactant-polymer flooding on ultimate recovery and net present value (NPV), given this capillary trapping. A series of numerical experiments was 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. These experiments were performed on two stylized reservoir models PUNQ-S3 and SPE10M reservoir models. Given our assumptions, the ultimate recovery did not significantly change with varying the CEOR implementation time. There is, however, an optimum implementation time for CEOR at which NPV is maximized. The optimum implementation time becomes sooner as the geologic model is more heterogeneous.

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Impact of Chemical Flood Mode on Oil Recovery in Fractured Carbonates

Cited by 2 publications

References 22 publications

Laboratory Investigations To Determine the Effect of Connate-Water Composition on Low-Salinity Waterflooding in Sandstone Reservoirs

Laboratory Investigations To Determine the Effect of Connate-Water Composition on Low-Salinity Waterflooding in Sandstone Reservoirs

Impact of Chemical Flood Implementation Time on Ultimate Recovery and Net Present Value

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