Phases of eor projects implementation

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EOR. Chemical methods

Phases of EOR projects implementation
Implementation of the EOR project is complex and long lasting process comprising the phases. In order to achieve a greater level of efficiency and reduction of risks and uncertainties of the project outcome, it is necessary to define the comprehensive management of the EOR process starting from EOR method selection, process designing, performing the pilot test and full implementation at the whole oil reservoir.
Phase 1 refers to the preliminary multi-criteria analysis in order to estimate the possibilities of application of adequate EOR methods at certain oil reservoir. Main properties of fluids and reservoir (potential candidate for the EOR method application), which are comparing to the criteria defined on the basis of laboratory results and practical results of a large number of EOR projects involve: oil viscosity and density, oil saturation, thickness, permeability, porosity, depth, reservoir temperature and pressure, formation type. Screening criteria for EOR processes are given in Table 13.1. Besides parameters in the table, additional criteria and considerations are needed depending on the method which possibility of using is estimated
EOR. Chemical methods
These processes use chemicals added to water in the injected fluid of a waterflood to alter the flood efficiency in such a way as to improve oil recovery. This can be done in many ways, examples are listed below:

  • Increasing water viscosity (polymer floods)

  • Decreasing the relative permeability to water (cross-linked polymer floods)

  • Increasing the relative permeability to oil (micellar and alkaline floods)

- Decreasing the interfacial tension between the oil and water phases (micellar and alkaline floods)

Figure 13.11. Chemical EOR
Chemical flood additives, especially surfactants designed to reduce surface or interfacial tension, are extremely expensive. Thus, the whole chemical EOR flood is designed to minimize the amount of surfactants needed, and to ensure that the EOR process is economically successful as well as technically. Chemical flooding is therefore not a simple single stage process. Initially the reservoir is subjected to a preflush of chemicals designed to improve the stability of the interface between the in-situ fluids and the chemical flood itself.
Then the chemical surfactant EOR flood is carried out. Commonly polymers are injected into the reservoir after the chemical flood to ensure that a favourable mobility ratio is maintained.
A buffer to maintain polymer stability follows, then a driving fluid, which is usually water, is injected. Figure 13.11 shows a typical flood sequence. Note that the mobilised oil bank moves ahead of the surfactant flood, and how the total process has reduced the amount of the surfactant fluid used.
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