Ineffective porosity, abbreviated as \( n_i \), also called closed porosity, a dimensionless number, is the fraction of the total pore volume in a reservoir rock sample where fluids such as hydrocarbons or water may be present but cannot participate in effective fluid flow or production. These pores are completely isolated, lacking any throat passages or connections to the surrounding pore network, which means there is no pathway for fluids to migrate toward a wellbore under natural or induced pressure gradients. As a result, hydrocarbons trapped within ineffective porosity contribute to the rock's overall storage capacity but are not recoverable through conventional or enhanced recovery processes, rendering this portion of the pore space non-contributory to reservoir performance.
Ineffective Porosity Formula
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\( n_i \;=\; \dfrac{ V_{dp} }{ V_b }\) (Ineffective Porosity) \( V_{dp} \;=\; n_i \cdot V_b \) \( V_b \;=\; \dfrac{ V_{dp} }{ n_i }\) |
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| Symbol | English | Metric |
| \( n_i \) = Ineffective Porosity | \(dimensionless\) | \(dimensionless\) |
| \( V_{dp} \) = Volume of Completely Disconnected Pores | \(in^3\) | \(cm^3\) |
| \( V_b \) = Bulk Volume | \(in^3\) | \(cm^3\) |
