Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting reservoir system quality and performance

  | chapter = Predicting reservoir system quality and performance

  | frompg  = 9-1

  | frompg  = 9-11

  | topg    = 9-156

  | topg    = 9-13

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

* Solution gas

* Solution gas

* Rock or compaction drive

* Rock or compaction drive

* Gravity drainage

* [[Gravity]] drainage

One type usually dominates, but drive types can occur in combination. Depending on the drive mechanism, characteristic recovery efficiencies can be expected for a given reservoir.

One type usually dominates, but drive types can occur in combination. Depending on the drive mechanism, characteristic recovery efficiencies can be expected for a given reservoir.

==Solution gas==

==Solution gas==

Crude oil under high pressure can contain large amounts of dissolved gas. The more gas there is in solution, the more compressible the oil. In oil reservoirs with little or no water drive, reservoir energy to drive the oil toward the wellbore can be supplied by expansion of the oil due to gas expanding in solution. This is a solution gas (or dissolved gas or depletion) drive. When pressure drops below the bubble point in the reservoir, small, disconnected gas bubbles form in pores, also pushing the oil toward the wellbore. At about 5–10% free gas in the reservoir, the bubbles coalesce and the gas moves toward the wellbore as a separate flowing phase. When this happens, oil production drops and gas production increases rapidly because of the increased relative [[permeability]] to gas.

[[Crude oil]] under high pressure can contain large amounts of dissolved gas. The more gas there is in solution, the more compressible the oil. In oil reservoirs with little or no water drive, reservoir energy to drive the oil toward the wellbore can be supplied by expansion of the oil due to gas expanding in solution. This is a solution gas (or dissolved gas or depletion) drive. When pressure drops below the bubble point in the reservoir, small, disconnected gas bubbles form in pores, also pushing the oil toward the wellbore. At about 5–10% free gas in the reservoir, the bubbles coalesce and the gas moves toward the wellbore as a separate flowing phase. When this happens, oil production drops and gas production increases rapidly because of the increased relative [[permeability]] to gas.

==Rock drive==

==Rock drive==

==Gravity drainage==

==Gravity drainage==

In gravity drainage, oil drains downward through a reservoir under the influence of gravity. This requires high vertical permeability or steeply dipping beds and thus is common in fractured reservoirs. Efficiency can be surprisingly high (75%+), especially where beds have steep dip, the oil has low viscosity, and the oil draining from the top of the column is replaced by exsolved gas.

In gravity drainage, oil drains downward through a reservoir under the influence of gravity. This requires high vertical permeability or steeply dipping beds and thus is common in fractured reservoirs. Efficiency can be surprisingly high (75%+), especially where beds have steep [[dip]], the oil has low [[viscosity]], and the oil draining from the top of the column is replaced by exsolved gas.

==Combination==

==Combination==

==Decline curves for drive types==

==Decline curves for drive types==

[[file:predicting-reservoir-system-quality-and-performance_fig9-7.png|thumb|{{figure number|2}}See text for explanation.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-7.png|thumb|300px|{{figure number|2}}See text for explanation.]]

Analysis of production decline curve shape can provide a good indication of the dominant drive mechanism. [[:file:predicting-reservoir-system-quality-and-performance_fig9-7.png|Figure 2]] compares typical production decline curves for the different drive mechanisms described above for a reservoir with approximately the same pore volume. It assumes all other factors are normalized.

Analysis of production decline curve shape can provide a good indication of the dominant drive mechanism. [[:file:predicting-reservoir-system-quality-and-performance_fig9-7.png|Figure 2]] compares typical production decline curves for the different drive mechanisms described above for a reservoir with approximately the same pore volume. It assumes all other factors are normalized.

==See also==

==See also==

* [[Reservoir system basics]]

* [[Reservoir system]]

* [[What is a reservoir system?]]

* [[Analyzing a reservoir system]]

* [[Analyzing a reservoir system]]

* [[Defining flow units and containers]]

* [[Defining flow units and containers]]

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]