Fluid saturation is how much each fluid is present in pore spaces of a rock. This will affect the ability of each fluid flow through porous media. This is one of critical values for reservoir engineering since many engineering calculations need fluid saturation values.
Fluid Saturation in Rock
Fluid saturation is expressed in terms of volume of fluid divided by total pore space.
Gas saturation (Sg) = Vg ÷ Vp
Oil saturation (So) = Vo ÷ Vp
Water saturation (Sw) = Vw ÷ Vp Continue reading
Absolute permeability is an ability to flow fluid through a permeable rock when only one type of fluid is in the rock pore spaces. The absolute permeability is used to determine relative permeability of fluids flowing simultaneously in a reservoir.
Darcy’s equation is widely used in an oil field to measure flow in porous media and the Darcy’s linear flow equation is shown below;
Compressibility is a relative volume change of a fluid or solid in a response to a pressure change. We can relate this into a reservoir engineering aspect. Overburden pressure is rock weight and it typically has a gradient of 1 psi/ft. Rock metric and formation fluid in pore spaces supports the weight of rock above. When petroleum is produced from reservoir rocks, pressure of fluid in pore space decreases, but overburden is still the same. This will result in the reduction of bulk volume of rock and pore spaces. The reduction on volume in relation to pressure is called “pore volume compressibility (cf)” or “formation compressibility” and it can be mathematically expressed like this.
Porosity is one of rock important rock properties and it is a measure of pore space in a rock.
Figure 1 – Porosity
(Ref: http://www.tulane.edu/~sanelson/images/pores.gif)
Figure 1 shows the illustration of porosity and it can be seen that grain size and distribution can affect porosity of rock.
Porosity (ɸ) is mathematically expressed as a ratio of total void space with a rock to a total volume of rock.
Where;
Vp = pore volume
Vb = bulk volume of rock
Porosity (ɸ) is shown in percentage form. Continue reading
