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     My question is the role of porosity in control oil and gas also and the importance of porosity in oil and gas.

Dear George Mrema,

My sincere apologies for delayed response to you. I thank you for sending me this question.

Here is my answer;

Porosity is the key component for oil and gas accumulation. Porosity is the ratio of the volume of interstices (pores or gaps) of a material to the volume of its mass. The pores are voids in between rocks grains.Take an example of rooms in a house so the rooms are porosity where people live while the oil and gas are being lived in porosity. More bigger the rooms more space for oil, water or gas storage. Porosity is expressed in percent of the rock mass.

In a mathematical expression; if  1 cubic meter rocks has 10 percent pores, means the pores storage  volumes would be 1/10 = 0.01 Cubic meter of oil or water.

There are two kind of natural Porosity in any rock 1)primary porosity which were developed at the time of the deposition of the rock 2) Secondary porosity which were developed after the deposition of the rock either due to mineralization (dolomitization or mineral replacement) or diagenesis (more than one mineral reaction with host rock) or by fracturing.

Bigger the porosity number more volume of oil and gas rock may store. The primary porosity in sandstone may vary from  as low as 5 percent to as high as 40 percent whereas limestone varies between 4 to 38 percent. In order to have a reservoir rock with excellent permeability pore structures should be connected with other pores which will allow oil and gas to flow freely. Some rocks have higher porosities such as shale and claystone but since their pores are not very well aligned and connected to each other the permeabilities are far too low than sandstones and limestones.

Keep in mind that during the life of any rock porosity has been reduced by cementation and compaction whereas diagenesis may enhance the porosity and peremability in certain cases.

Hope this answer helps you well.




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Syed Tariq Hasany


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