Permeability Determination with Ruska Gas Permeameter.

INTRODUCTION

Hello everyone, will be writing an article about the experiment which was carried out in the laboratory on determining the permeability of a core(rock) sample using ruska gas permeameter.

What is permeability?

Permeability is the property of a porous medium( rock) to transmit fluid. In reality permeability is a rock property which determines the transmission of fluid in the subsurface. The rock that has this property is sedimentary rock. Permeability controls the directional movement and flow rate of reservoir fluid in the formation ( a geologic subsurface structure which have property of porosity, permeability)

Description of apparatus

Ruska gas permeameter which measures the permeability of consolidated core section by forcing gas of known viscosity through the core sample of known cross sectional area and length. The equipment consists of; Core holder with built in thermometer, triple range flow meter with selector valve, hand calibrated burden tube pressure gauge, pressure regulator, gas inlet connection.

^{ruska gas permeameter}

^{Nitrogen cylinder used for experiment}

Theory

The theory behind permeability determination is Darcy's law and Klinkenbergs effect which is used to correct the obtained permeability.

Darcy's law

This mode of rock characterization was first defined mathematically by Henry Darcy in 1856. It states that the velocity of a homogenous fluid in a porous medium is proportional to the pressure gradient and inversely proportional to the fluid viscosity.

where ν = apparent fluid flowing velocity, cm/sec
k = proportionality constant, or permeability, Darcy’s
μ = viscosity of the flowing fluid, cp
dp/dL = pressure drop per unit length, atm/cm

The equation is true for the following assumptions

1. Laminar flow takes place
2. The pore space is 100% saturated with flowing fluid.
3. The flow of fluid is in horizontal direction hence gravity will be neglected.

Klinkenberg effect

In 1941, Klinkenberg discovered that permeability measured with air as flowing fluid show different value from permeability measured with liquid as flowing fluid. Klinkenberg then postulated from laboratory experiment, the liquid had zero velocity at the sand grain surface, while gases had finite velocity at the sand grain surface. Klinkenberg also found out that for a given medium that is porous as the mean pressure increased the calculated permeability decreased.
Mean pressure: this is defined as the upstream flowing pressure plus downstream pressure divided by two, [Pm=(P1+P2) /2].
The magnitude of Klinkenberg effect vary with the core permeability and type of gas used for the experiment.

where kg = measured gas permeability
pm = mean pressure
kL = equivalent liquid permeability, i.e., absolute permeability, k
c = slope of the line

PROCEDURE

1. Ensure that care has been extracted and thoroughly dried

2. Push core into a rubber stopper of the corresponding hole size and insert it into the core holders sleeve and lock tight in the core holder.

3. Connect the Nitrogen cylinder to the gas inlet connection of the apparatus and ensure all connections are gas tight.

4. Turn the selector valve on the flow meter to LARGE.

5. Turn the T-screw on the Nitrogen cylinder gradually until the pressure gauge reads 0.25 atmosphere. Tap the gauge glass slightly while the pressure is being adjusted. If the float in the large tube rises above 20 divisions a reading is taken.

6. if the reading remains below 20 divisions turn the selector valve to MEDIUM nd turn the T screw on the gas cylinder to increase the pressure to 0.5 atmospheres.

7. if the float fails to rise in either large or medium tubes at their rated pressure turn the selector valve further to small and increase the pressure to 1.0 atmosphere.

8. When the proper flow meter tube has been determined by the above procedure readings are taken to the nearest division estimating the centre of the suspended float.

9. Record the operating temperatures, close off gas supply, remove the core sample and measure its length and diameter.

10. With the charts attached, read out the corresponding viscbsity of Nitrogen at the operating temperature and the average flow rate Q, in cmB/sec.

Graph from result

ERROR ANALYSIS

During this thesis, the experiments carried out gave fairly consistent results. However certain human and equipment error must be considered. An example of this is error in measuring time for fluid to flow t. This error would give an error in the flow rate since q=V/t and finally in the permeability value since the permeability is a function of flow rate.

PRECAUTIONS

• Carefully and slowly opened the valve with the proper regulator in place.
• Familiarized myself with potential hazards associated with the gas permeameter, emergency shutdown procedures as well as the operating procedures.
• It was ensured that there were no leaks in the gas system.
• Followed direction for opening and closing the valves.

CONCLUSION

The permeability experiment carried out using the Ruska gas permeameter produced fairly consistent result but improves can be made by acquiring a permeameter using a digital timer.

REFERENCES

• Laboratory manual
• Monicard, R. P., Properties of Reservoir Rocks: Core Analysis. Gulf Publishing Co., Houston, TX (1980)
• Amyx, J.W., Bass, D.M., and Whiting R.L., Petroleum Reservoir Engineering, McGraw￾Hill, New York, NY (1960)
• Engler, T.W., Fluid Flow in Porous Media – Notes of Class Petroleum Engineering 524 –
  Fall 2003.
• Basic reservoir engineering by Rene Cosse.
  

Thanks for reading through

All the images used are original