Category Archives: Drilling Fluids

Gel Strength and Operational Impact

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The gel strength is the shear stress of drilling mud that is measured at a low shear rate after the drilling mud has been static for a certain period of time. The gel strength is one of the most important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solid and weighting material when circulation is ceased.

gel-strenght

How can gel strength is measured?

Gel strength measurement is made on viscometer using the 3-rpm reading, which will be recorded after stirring the drilling fluid at 600 rpm to break gel. The first reading is noted after the mud is in a static condition for 10 seconds. The second reading and the third reading will be 10 minutes and 30 minutes, respectively. Continue reading →

Yield Point (YP) of Drilling Fluids

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Yield Point (YP) is resistance of initial flow of fluid or the stress required in order to move the fluid. It can be simply stated that the Yield Point (YP) is the attractive force among colloidal particles in drilling fluid. As per Bingham plastic model, YP is the shear stress extrapolated to a shear rate of zero.

Figure 1 - YP is a shear stress at zero shear rate.

Figure 1 – YP is a shear stress at zero shear rate. Continue reading →

Viscosity of Drilling Mud

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Viscosity describes a substance’s resistance to flow. High-viscosity drilling mud is typically described as “thick,” while low-viscosity mud is characterized as “thin”. In the oilfield, the following terms are used to describe drilling fluid viscosity and rheological properties. Two viscosities that will be described in this section are Funnel Viscosity and Plastic Viscosity.

 Funnel Viscosity

The funnel viscosity is timed in seconds of drilling mud flowing through the Marsh Funnel Viscosity. The Marsh funnel is easy-to-use equipment that is used to quickly check viscosity of the mud. The Marsh funnel is dimensioned so that the outflow of time of one quart of freshwater (946 cc) at a temperature of 70 F ± 5 F (21 C ± 3 C) in 26 ± 0.5 seconds.

Figure 1 - Marsh Funnel

Figure 1 – Marsh Funnel Continue reading →

Mud Weight and Its Importance in Drilling

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Mud weight or mud density is a weight of mud per unit volume. It is one of the most important drilling fluid properties because it controls formation pressure and it also helps wellbore stability. Mud weight is measured and reported in pounds per gallon (PPG), pounds per cubic feet (lb/ft3), or grams per milliliter (b/ml).
Mud weight is normally measured by a conventional mud balance; however, if you have some air inside a fluid phase, reading from the conventional mud balance will give you an inaccurate number. Therefore, the most accurate method to measure the mud weight is with a pressurized mud balance.

conventional mud balance

Conventional Mud Balance

Pressurized Mud Balance

Pressurized Mud Balance

The pressurized mud balance looks like the convention one, but it has a pressurized sample cup. When you press a mud sample into the cup, any gas in a fluid phase is compressed to a very small volume so the mud weight measurement is more accurate. Continue reading →