The most common procedure for determining the optimum time to start waterflooding is to calculate:

• Anticipated oil recovery

• Fluid production rates

• Monetary investment

• Availability and quality of the water supply

• Costs of water treatment and pumping equipment

• Costs of maintenance and operation of the water installation facilities

• Costs of drilling new injection wells or converting existing production wells into injectors

These calculations should be performed for several assumed times and the net income for each case determined. The scenario that maximizes the profit and perhaps meets the operator's desirable goal is selected.

Cole (1969) lists the following factors as being important when determining the reservoir pressure (or time) to initiate a secondary recovery project:

• Reservoir oil viscosity. Water injection should be initiated when the reservoir pressure reaches its bubble-point pressure since the oil viscosity reaches its minimum value at this pressure. The mobility of the oil will increase with decreasing oil viscosity, which in turns improves the sweeping efficiency.

• Free gas saturation. (1) In water injection projects. It is desirable to have initial gas saturation, possibly as much as 10%. This will occur at a pressure that is below the bubble point pressure. (2) In gas injection projects. Zero gas saturation in the oil zone is desired. This occurs while reservoir pressure is at or above bubble-point pressure.

• Cost of injection equipment. This is related to reservoir pressure, and at higher pressures, the cost of injection equipment increases. Therefore, a low...