Tag Archives: engineering

Determine Compressibility of Gases

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This article will demonstrate how to determine gas compressibility by using simplified equation of state.

At a low pressure condition, gas similarly behaves like ideal gas and the equation for the ideal gas law is listed below;

PV = nRT

Where;

P = pressure

V = gas volume

T = absolute temperature

n = number of moles of gas

R = gas constant

Gas constant (R) is different because it depends on the unit system used in the calculation. The R in the different unit system is demonstrated in the below table.

1 table for R

Table 1 – Gas Constant (R) at Different Unit

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Volumetric Method To Estimate Volume In Place and Reserves

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Volumetric is a method to estimate fluid in reservoir based on volume of pore space in a rock and water saturation.

Volume of Oil Initially In Place (OIIP)

To estimate oil initially volume in place, the following formula is a volumetric calculation for oil.

STOIIP

Where;

STOIIP = stock tank oil in place, stb

A= area, acre

h = reservoir thickness, ft

ɸ = rock porosity, %

Swc =connate water saturation, %

Boi = oil formation volume factor, rb/stb

Note: the stock tank condition is a standard surface condition of oil and gas at 60F and 14.7 psia. Continue reading →

Material Balance for a Water Drive Mechanism

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This article will demonstrate a material balance equation in a natural water drive mechanism.  A full material balance equation is shown below:

Figure 1 - Full Material Balance Equation

Figure 1 – Full Material Balance Equation

Assumptions

  • Reservoir pressure above the bubble point (Pb). Above a bubble point, Rs = Rsi.
  • No water injection
  • No gas injection
  • No gas cap
  • Neglect formation and connate water compressibility (Cf and Cw have little effect for a gas cap drive mechanism.)
Figure 2 - Material Balance Equation with Assumption for a Natural Water Drive Mechanism

Figure 2 – Material Balance Equation with Assumption for a Natural Water Drive Mechanism

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Material Balance for Gas Cap Drive Mechanism

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This article will demonstrate a material balance equation in gas cap drive mechanism.  First, we start with a full material balance equation.

Figure 1 - Full Material Balance Equation

Figure 1 – Full Material Balance Equation

Assumptions

  • No water production
  • No water injection
  • No gas injection
  • No water influx
  • Neglect formation and connate water compressibility (Cf and Cw have little effect for a gas cap drive mechanism.)

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Solution Gas Drive Mechanism Explained in Material Balance Equation

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Material balance equation can be applied for any drive mechanism and this article demonstrates how to apply the material balance equation in a solution drive mechanism. For a solution drive mechanism, there are 2 cases. The first case is when reservoir pressure is above a bubble point and the second case is when reservoir pressure is below a bubble point.

Solution Gas above Bubble Point

Start with a full material balance equation.

Figure 1 - Full Material Balance Equation

Figure 1 – Full Material Balance Equation

Assumptions Continue reading →