Oil and Gas 101::: Porosity, Permeability, Pressure ::: Amerex Corporation :::

Glossary of Terms :: Porosity, Permeability, Pressure :: Directional Drilling :: Oil Well Diagram :: Secondary Recovery :: Oil and Gas History

There are three elements essential for fluid extraction within a resource bearing reservoir. Porosity, Permeability, and Pressure are the necessary factors for removal of these resources, and must be present together in order for a well to be commercially viable.

  • Porosity: The percentage of pore volume or void space;
  • Permeability: The measurement of the ability to transmit fluids;
  • Pressure: The pressure of fluids within the pores of a reservoir;

Porosity is a rocks ability to store fluids within it. Effective porosity is the volume containable through the interconnected pores, and is usually less than total porosity. Thus, porosity alone is not enough to ensure that fluids can move through a rock structure. These pores must be interconnected in order to have any chance of a predicable reservoir.

Permeability, as defined above, is a rocks ability to move fluids. Permeability is directly related to a formations Effective Porosity, as these interconnections within a rocks structure are the necessary transmission lines for a fluid to flow. The largest reservoir, with little to no porosity and permeability, is useless.

Pressure, in this instance, is the amount of force a fluid exerts within the pores of a reservoir. Pressure within a reservoir changes over time, therefore it is necessary to define a reference, which in this case would be the Initial Pressure. Good reservoir pressure is the third essential element for resource recovery.

To understand how these three necessities work together, we need only to look to the common sponge. A sponge, to be useful, must have good Porosity and Permeability. This is what gives a sponge the natural ability to store fluids. But how do we get the fluid out of the pores. In the instance of a sponge, this is easy, as any kind of pressure applied will cause the sponge to give up the fluids. Nature, aside from the sponge, is rarely so obliging when it comes to the recovery of natural resources.

The oil and gas industry has come up with many ways to increase porosity and elevate reservoir pressure. The most common way to increase porosity is to fracture (frac) the targeted zone. This entails setting off a focused charge within the pipe, at a predetermined depth, in order to reach the zone targeted for production. This charge puts holes in the pipe, as well as breaks up the rock in the immediate area of the blast. These holes are used as an access point for a fracturing fluid to be injected into the zone. Different zones require different types of fluids and mixtures to be effective, most common are the acid salt mixtures. Injected with these mixtures is generally a large amount of water, at high pressures. This mixture and pressure combined is a highly effective means of increasing porosity.

Increased porosity is only half the story. Without the necessary reservoir pressures, porosity becomes moot. The industry has devised many different ways to combat low pressures, the most common being the pumpjack. The pumpjack however, only creates suction, and does nothing to increase pressures. One remedy for lower pressures are injection wells, that replace fluids as they are taken, or even moves fluids towards the producing well.

The best solution for managing pressure within a well is to maintain the initial pressures as long as possible. For example, a can of spray paint can last for an extended period of time by stirring the paint and maintaining a proper spraying angle. The manufacturer sets the choke at the top of the can to moderate the rate of flow. Cut the top of the can off however, and what you have left is no pressure and a lot of paint that not easily obtained for its intended use.

A well has similar properties. An operator can open the bore completely, and produce at extremely high numbers for a short period of time. But to get the highest rate of return possible, managing Porosity, Permeability, and Pressure is key.



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