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[[file:drive-mechanisms-and-recovery_fig1.png|thumb|{{figure_number|1}}Reservoir pressure trends by drive mechanism.]]

[[file:drive-mechanisms-and-recovery_fig2.png|thumb|300px|{{figure_number|2}}Producing gas-oil ratio trends by drive mechanism.]]

 

[[file:drive-mechanisms-and-recovery_fig2.png|thumb|{{figure_number|2}}Producing gas-oil ratio trends by drive mechanism.]]

The natural energy of a reservoir can be used to move oil and gas toward the wellbore. Used in such a fashion, these sources of energy are called ''drive mechanisms''. Early determination and characterization of the drive mechanism(s) present within a reservoir may allow a greater ultimate recovery of hydrocarbons. Drive mechanisms are determined by the analysis of historical production data, primarily reservoir pressure data and fluid production ratios.

The natural energy of a reservoir can be used to move oil and gas toward the wellbore. Used in such a fashion, these sources of energy are called ''drive mechanisms''. Early determination and characterization of the drive mechanism(s) present within a reservoir may allow a greater ultimate recovery of hydrocarbons. Drive mechanisms are determined by the analysis of historical production data, primarily reservoir pressure data and fluid production ratios.

==Production trends==

==Production trends==

[[file:drive-mechanisms-and-recovery_fig3.png|thumb|{{figure_number|3}}Solution gas drive reservoir.]]

[[file:drive-mechanisms-and-recovery_fig3.png|thumb|300px|{{figure_number|3}}Solution gas drive reservoir.]]

Solution gas drive reservoirs show characteristic changes in reservoir pressure, producing gas-oil ratio, and oil and water production rates during the life of the reservoir. If the reservoir is initially undersaturated, the reservoir pressure falls quickly during oil production because of the small compressibilities of oil, water, and rock. Pressure drops of several hundred pounds per square inch can easily occur over a matter of months. Because the only gas produced is that which evolves from the produced oil in the wellbore, the gas-oil ratio (GOR) remains constant until the reservoir reaches the bubblepoint.

Solution gas drive reservoirs show characteristic changes in reservoir pressure, producing gas-oil ratio, and oil and water production rates during the life of the reservoir. If the reservoir is initially undersaturated, the reservoir pressure falls quickly during oil production because of the small compressibilities of oil, water, and rock. Pressure drops of several hundred pounds per square inch can easily occur over a matter of months. Because the only gas produced is that which evolves from the produced oil in the wellbore, the gas-oil ratio (GOR) remains constant until the reservoir reaches the bubblepoint.

In a gas cap drive reservoir, the primary source of reservoir energy is an initial gas cap, which expands as the reservoir pressure drops ([[:file:drive-mechanisms-and-recovery_fig4.png|Figure 4]]). Additional energy is provided by the expansion of solution gas released from the oil. Less significant drive contributions are provided by the expansion of the rock and its associated water.

In a gas cap drive reservoir, the primary source of reservoir energy is an initial gas cap, which expands as the reservoir pressure drops ([[:file:drive-mechanisms-and-recovery_fig4.png|Figure 4]]). Additional energy is provided by the expansion of solution gas released from the oil. Less significant drive contributions are provided by the expansion of the rock and its associated water.

[[file:drive-mechanisms-and-recovery_fig4.png|thumb|{{figure_number|4}}Gas cap drive reservoir.]]

[[file:drive-mechanisms-and-recovery_fig4.png|thumb|300px|{{figure_number|4}}Gas cap drive reservoir.]]

===Production trends===

===Production trends===

The geometry of the aquifer determines whether it is a ''bottom water'' or an ''edge water'' drive ([[:file:drive-mechanisms-and-recovery_fig5.png|Figure 5]]). In a bottom water drive, the aquifer is present below the entire reservoir and water influx moves vertically upward into the oil zone. In an edge water drive, the aquifer is located on the flanks of the reservoir and the water moves upward along the reservoir dip.

The geometry of the aquifer determines whether it is a ''bottom water'' or an ''edge water'' drive ([[:file:drive-mechanisms-and-recovery_fig5.png|Figure 5]]). In a bottom water drive, the aquifer is present below the entire reservoir and water influx moves vertically upward into the oil zone. In an edge water drive, the aquifer is located on the flanks of the reservoir and the water moves upward along the reservoir dip.

[[file:drive-mechanisms-and-recovery_fig5.png|thumb|{{figure_number|5}}Edge water versus bottom water drive reservoirs.]]

[[file:drive-mechanisms-and-recovery_fig5.png|thumb|300px|{{figure_number|5}}Edge water versus bottom water drive reservoirs.]]

===Production trends===

===Production trends===

==Combination drive==

==Combination drive==

[[file:drive-mechanisms-and-recovery_fig6.png|thumb|{{figure_number|6}}Combination drive reservoir.]]

[[file:drive-mechanisms-and-recovery_fig6.png|thumb|300px|{{figure_number|6}}Combination drive reservoir.]]

Most oil reservoirs produce under the influence of two or more reservoir drive mechanisms, referred to collectively as a combination drive. A common example is an oil reservoir with an initial gas cap and an active water drive ([[:file:drive-mechanisms-and-recovery_fig6.png|Figure 6]]).

Most oil reservoirs produce under the influence of two or more reservoir drive mechanisms, referred to collectively as a combination drive. A common example is an oil reservoir with an initial gas cap and an active water drive ([[:file:drive-mechanisms-and-recovery_fig6.png|Figure 6]]).

==Gravity drainage==

==Gravity drainage==

[[file:drive-mechanisms-and-recovery_fig7.png|thumb|{{figure_number|7}}Fluid segregation by gravity damage.]]

[[file:drive-mechanisms-and-recovery_fig7.png|thumb|300px|{{figure_number|7}}Fluid segregation by gravity damage.]]

Gravity drainage, or gravity segregation, is the tendency of oil, gas, and water to segregate in a reservoir during production due to their differing densities ([[:file:drive-mechanisms-and-recovery_fig7.png|Figure 7]]). As a secondary drive mechanism, gravity drainage occurs only in combination with one or more of the primary oil reservoir drive mechanisms.

Gravity drainage, or gravity segregation, is the tendency of oil, gas, and water to segregate in a reservoir during production due to their differing densities ([[:file:drive-mechanisms-and-recovery_fig7.png|Figure 7]]). As a secondary drive mechanism, gravity drainage occurs only in combination with one or more of the primary oil reservoir drive mechanisms.