The routine Gas Material Balance is often associated with analyzing the role of aquifer, its strength, and identifying the best model to find exact behavior of aquifer and GIIP. Doing so, the reservoir history matching and predicting its future performance is a function of proper estimation of aquifer model.
I am looking for a valid numerical example of a Gas Material Balance with Aquifer. Appreciate if any one provides with data and information.
The type of example you are looking for is rare, because a valid model of both gas and water legs require accurate measurements not only in the gas reservoir, but also in the aquifer below the Gas Water Contact (GWC). The aquifer may be lateral, or deeper than most of the existing wells. Accurate testing of the aquifer may be outside the scope of the discovery well operator.
A tricky but not so uncommon case is given by a gas field in a clastic reservoir with a rather tight (but not completely impermeable) aquifer below. This is normally due to differential reservoir rock diagenesis, with porosity preservation in the gas leg and enhanced sand cementation in the water leg.
In this case, during the field productive life, the gas looks like subject to pure gas expansion drive, but in the long run (tens of years) the water slowly and inexorably encroaches in the gas leg, slowing somehow the normal gas pressure decline during production. After tens of years after the end of gas production, the water invades the structurally lower part of the gas reservoir and the residual gas is found concentrated and almost completely repressurized in the structural apex of the trap.
This case is particularly relevant if you want to use the semi-depleted gas field for Underground Gas Storage (UGS) tens of years after the last gas production.
In Italy, overlooking this long term behaviour is causing serious problems to the developers of new gas storage sites in semi-depleted gas fields with Pliocene or Miocene sandstone reservoir.
Reza,
I am sorry but this comes from my experience with many actual gas projects, in Italy and elsewhere. I am not aware of published data sets or documents about the above.
Best regards
Roberto
@Reza
You could use an artificial model, e.g. you set up a small gas reservoir case with aquifer support in Eclipse, and use the results of Eclipse with your MB calculation. In this way you can easily vary aquifer strength / behavior, and see its effect on your MB.
@Roberto
I've seen this delayed aquifer effect you describe in an oil reservoir. After a while reservoir pressure started to rise, and nobody really knew why. It was the delayed effect of a slow reacting aquifer. I've elaborated a method to quantify this, so if you think, I could try to analyze your data.
You may want to check out our recent paper on this topic. I can share one or two simulated cases as identified in Table 1 of the attached paper. In that case, I'll need your email address.
Dear Shah,
Excellent paper. I would be glad to receive your data sets. My e-mail is: [email protected] Thank you very much in advance,
best regards
Andras
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