FACTORS TO CONSIDER IN WATERFLOODING

To determine the suitability of a candidate reservoir for waterflooding, the following reservoir characteristics must be considered:

? Reservoir geometry

? Fluid properties

? Reservoir depth

? Lithology and rock properties

? Fluid saturations

? Reservoir uniformity and pay continuity

? Primary reservoir-driving mechanisms

Reservoir Geometry

The areal geometry of the reservoir will influence the location of wells and, if offshore, will influence the location and number of platforms required.?

The reservoir’s geometry will essentially dictate the methods by which a reservoir can be produced through water-injection practices.

Fluid Properties

The physical properties of reservoir fluids, particularly crude oil viscosity, significantly impact the viability of waterflooding for reservoir development.

Oil viscosity affects the mobility ratio, which in turn controls the sweep efficiency in a waterflooding project.

Reservoir Depth

Reservoir depth affects both technical and economic factors in secondary or tertiary recovery projects, influencing maximum injection pressure and economic water-oil ratios, which in turn impact recovery and operating costs.

Shallow reservoirs limit injection pressure to avoid exceeding fracture pressure, with a critical pressure of approximately 1 psi/ft depth, requiring an operational pressure gradient of 0.75 psi/ft to prevent fracturing and water bypassing.

Lithology and Rock Properties

Reservoir lithology and rock properties that affect flood ability and success are:?

? Porosity?

? Permeability?

? Clay content?

? Net thickness

Fluid Saturations

A high oil saturation is the primary criterion for determining a reservoir's suitability for waterflooding, as it ensures a sufficient supply of recoverable oil.

Higher oil saturation at the start of flooding operations enhances oil mobility, leading to increased recovery efficiency.

Reservoir Uniformity and Pay Continuity

Substantial reservoir uniformity is crucial for successful waterflooding, as high-permeability zones (thief zones) can cause rapid channeling and bypassing, leading to high water-oil ratios and reduced profitability unless isolated.

Areal continuity of the pay zone is essential for effective flooding, with isolated lenses requiring both injectors and producers, and any reservoir anisotropy or discontinuities must be identified to design an appropriate well placement and flood pattern.

Primary Reservoir-Driving Mechanisms

6 driving mechanisms basically provide the natural energy necessary for oil recovery:?

? Rock and liquid expansion?

? Solution gas drive?

? Gas-cap drive?

? Water drive?

? Gravity drainage drive?

? Combination drive

Primary recovery refers to the production of hydrocarbons from a reservoir using only the natural energy of the reservoir, without supplementary processes like water-injection.

The primary drive mechanism and expected ultimate oil recovery should be considered when evaluating waterflood prospects, with approximate oil recovery ranges for various driving mechanisms provided, though actual recovery may vary.

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