Reservoir simulator benchmark tests

Brief

Before running any 3D reservoir simulator for a full scale field history matching or forecasts it is a good practice to make sure that simulator is performing well on a simple benchmark tests with well known analytical solutions.

Calculating well potential (well inflow performance)

If you eat the can of beans fast then the can doesn’t last as long as if you eat it slow, but you still eat the same amount of beans.

Same logic is true for the gas reservoir with the bottom water.

There is a fixed volume of gas above the water.  When you remove the gas the water moves up. You can do it slow or fast but the volume of gas above the water is the same. The water level will raise Gravity stable as defined by Newton’s Law.

Simulation Runs

Now let's attach the infinite aquifer to the can of gas and run scenarios:

1. Slow - choked gas rate
2. Fast - 2x enhanced gas rate

Oh no, water killed the well quick in the "Fast" case! We told you what! Right, but … which case produced more gas?

Gas Recovery

12% more recovery with the enhanced production over 20 years. Why?

Because of the pressure! The lower the reservoir pressure the more gas is produced before the water hits the perfs. It’s just physics!

Math and Physics

According to the Boyle's law (1662):

$PV = constant$

where P is pressure, V is volume.

In our case

$PV = constant = P_1V_1 = P_2V_2=P_{res}V_{res}$

The gas produced volume of the "Slow case"

$V_1 = \frac{P_{res}V_{res}}{P_1}$

The gas produced volume of the "Fast case"

$V_2 = \frac{P_{res}V_{res}}{P_2}$

And V₂ > V₁ because P₂ < P₁. The lower the P₂ gets over P₁ the higher the incremental recovery will be.

Summary

Produce gas reservoirs fast to increases recoveries.

If you have an aquifer you have to produce fast.

If you don’t have an aquifer…, so you don’t have water to complain.

Video

Watch our video explaining the gas reservoir production using the Can Of Beans (Gas) as an example

Model overview

• Cylindrical grid (10x10x30)
• re=500m, rw=0.1m, h=30m
• kx=ky=5mD, kz/kx=0.1, phi=0.2
• Pi=300bar, hres=3000m
• Gas and water PVT model
• SGgas=0.58
• Aquifer at the bottom (CT infinite extent)
• qgas_slow = 100 000 m3/d
• qgas_fast = 200 000 m3/d

3D reservoir simulation software

• ECLIPSE
• tNavigator
• CMG
• Waiwera

See also

• Petroleum Engineering
• Hydraulic fracturing
• 29+ reasons why you can not increase the production

References

By Mikhail Tuzovskiy on 20230712124339