Author Archives: DrillingFormulas.Com

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Working in the oil field and loving to share knowledge.

Capillary Pressure

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Capillary pressure is a force due to differentials between fluid densities in a rock that can force pull hydrocarbon through the pores of a rock so a transition zone between fluids occurs.

Let’s make it simple. If we put a small tube in water overlaid by oil, water will rise up into the tube due to capillary pressure (Pc). For this situation, the capillary pressure (Pc) is the difference in pressure across the curved interface between the fluids (oil and water) shown in Figure 1.

Figure-1-Capillary-Diagram

Figure 1 – Capillary Diagram Continue reading →

Rock Wettability

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Wettability is a tendency of fluid to stick to the surface of formation when other types of fluid are present. Wettability of rock is measured by a core analysis in a laboratory and typically a laboratory measure contact angle between the fluid and the rock.

Wettability of rock is classified by the angle of contact, which is divided into 3 categories.

Water wet – contact angle (θ) is less than 90 degrees

Figure-1---Water-Wet

Figure 1 – Water Wet Continue reading →

Fluid Saturation

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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

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 →

Types of Flow and Rheology Models of Drilling Mud

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When you learn about drilling mud, the rheological models are essential knowledge. The rheological models are critical for a drilling fluid study because they are used to simulate the characteristics of drilling mud under dynamic conditions. With this knowledge, you will be able to determine some of the key figures, such as equivalent circulating density, pressure drops in the system, and hole cleaning efficiency.

The drilling fluid has three flow regimes, plug flow, laminar flow and turbulent flow and Figure 1 demonstrates 3 flow regimes on the shear rate and shear stress curve. In between each zone, there is a transition zone where the flow regimes are changing.

Figure 1 – Various flow types

Figure 1 – Various flow types Continue reading →

Absolute Permeability

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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.

Absolute-Permeability---cover

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;

Darcy's equation Continue reading →