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Gas Drive Reservoir Production Stages

The document outlines 4 stages of production for pure solution gas drive reservoirs: 1) Production while undersaturated with no free gas and a stable GOR. 2) Production while saturated with small, immobile pockets of free gas and a slightly lower GOR. 3) Production while saturated with mobile free gas causing the GOR to increase steadily over the longest stage. 4) Production while saturated with a very low pressure and decreasing GOR, though primary recovery often ends before this stage.

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Jitendra Kumar
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72 views2 pages

Gas Drive Reservoir Production Stages

The document outlines 4 stages of production for pure solution gas drive reservoirs: 1) Production while undersaturated with no free gas and a stable GOR. 2) Production while saturated with small, immobile pockets of free gas and a slightly lower GOR. 3) Production while saturated with mobile free gas causing the GOR to increase steadily over the longest stage. 4) Production while saturated with a very low pressure and decreasing GOR, though primary recovery often ends before this stage.

Uploaded by

Jitendra Kumar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Stages of production

Pure solution gas drive reservoirs are subject to four stages of idealized production. In chronological order,
the four stages are:
1. Production while undersaturated
2. Production while saturated but the free gas is immobile
3. Production while saturated and the free gas is mobile and the producing gas-oil ratio (GOR) is
increasing
4. Production while saturated and the free gas is mobile and the producing GOR is decreasing
Not all these stages are necessarily realized. For instance, Stage 4 may not be realized if primary recovery
is terminated during Stage 3.
The key characteristics of each stage are outlined here.

Stage 1

No free gas

Producing GOR is equal to initial dissolved GOR

Fractional oil and gas recoveries are small and approximately equal

Reservoir pressure drops rapidly

Duration of stage depends on degree of initial undersaturation. The greater the initial
undersaturation, the longer the duration of Stage 1. The stage duration is generally short

Stage 2

Reservoir pressure is less than bubblepoint

Free gas appears, but the saturation is small and immobile

Producing GOR is slightly less than initial dissolved GOR

Rate of pressure decline is mitigated

Stage 3

Free gas becomes mobile

Producing GOR increases steadily

Fractional gas recovery exceeds fractional oil recovery

Longest of all stages; typically consumes 85 to 95% of primary recovery

Primary recovery may be terminated during this stage

Stage 4

Reservoir pressure is very low, typically less than 100 to 400 psia

Producing GOR decreases

Primary recovery often terminated before this stage is realized

This chronology and these characteristics are an idealization and oversimplification of actual behavior;
nevertheless, they are instructive and provide a preliminary basis for understanding scenarios that are
more complicated.

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