[TOOL BOX]:
Prompt quiz: We’ve said that most drilling mud should have a PH of 9 or greater. Will the mud be called acidic or alkaline?

Caustic Soda
Because mud needs to have a high PH, another common mud additive is Caustic Soda or Sodium Hydroxide. Caustic soda is often called “caustic”. Crew members add caustic soda to the mud to control PH. Caustic soda increases the PH value, it makes the mud more alkaline. In general, caustics are the most dangerous chemicals that you’ll handle on the rig. High strength solutions can seriously burn your skin. Be very careful when handling it to avoid injury, wear the proper personal protective equipment, also remember to always add caustic soda to water, never add water to caustic soda. If you do, the caustic soda will boil up, splatter and cover you with a burning chemical.

Gelled Mud
When drilling stops, say let the crew make a connection (add a joint of drill pipe to the string), the driller normally stops pumping mud. When pumping stops, the mud stops moving. At rest, mud gels, that is it becomes a semi-solid like gelatin. Gelled mud suspends the cuttings. Gelling keeps the cuttings from falling down hole and piling up around the bit. The ability of a gel to keep the cuttings suspended is measured by its gel strength. When the driller starts the pump and resumes mud’s circulation, the mud’s gel strength reduces, which allows the drilling fluid to flow easier.

MUD TESTS

Overview
We’ve just covered a few key points about mud additives and the properties that mud should have to allow a successful drilling. On the rig, it is important for crew members to constantly monitor and maintain these properties. An important member of the drilling team is the mud engineer. The mud engineer runs tests on the drilling fluid. The mud engineer’s job is to monitor and maintain the mud’s properties to the specifications of the well operator. He may also recommend changes to improve drilling, such as adding more caustic soda to increase the mud’s PH. In this section, we will learn about tools that’re used to monitor mud properties.

Mud Balance
The density, or weight per unit volume of the drilling mud determines how much hydrostatic pressure the mud column exerts on the formation. It is therefore important to know the mud’s density at all times. To determine mud density, the mud engineer or helper uses a mud balance. The person weighing the mud puts a small amount of mud in the mud container at left on the balance. He then slides the adjustable counterweight to the right or left until the arm balances on the fork room. The person then reads the mud density at the point on the arm next to the counterweight. In many areas, mud density is read in pounds per gallon but can also be reported in pounds per cubic foot, milligrams per liter, and other units. Mud density is usually called mud weight by the rig crew.

[TOOL BOX]: Calculate the density of mud by adjusting the counterweight on the mud balance. Click on the correct density when you’ve finished.

Marsh Funnel
The viscosity of the mud is thickness or resistance to flow, is also an important factor. The mud’s viscosity determines how well it can carry cuttings up the hole. One measure of a mud’s viscosity is its funnel viscosity. That is how many seconds does it take exactly one quart of mud to flow out of a special funnel called a Marsh Funnel. A Marsh Funnel has a hole in the bottom that’s the standard size. The mud engineer or helper pours one quart of mud into the funnel and records the time that it takes to run out into a pitcher or beaker. In this example, one quart of mud flows out of the funnel and into the beaker in 35 sec, so this mud has a funnel viscosity of 35 sec. A less viscous or thinner mud would flow through the funnel faster; a more viscous or thicker mud would flow through the funnel slower.

Rotational Viscometer
This device also measures mud’s viscosity. It is a more scientific viscosity measure than the Marsh Funnel. A Fann V-G Meter measures the mud’s viscosity in centipoises. A centipoise is a unit of measure for viscosity, just as an inch is a unit of measure for length. The Fann V-G Meter works by spinning a rotor or bob in a sample of mud at two different speeds. In addition, a Fann V-G Meter is used to determine a mud’s yield point, which is a measure of the mud’s resistance to flow. Combined with a timer, the Meter also measures the mud’s gel strength. Gel strength is the mud’s ability to temporarily solidify or gel when it’s not flowing.

[TOOL BOX]: Here’s a mud with high gel strength. Click the button labeled “lower gel strength” to see what would happen if the gel strength wasn’t this high.

Filter Press
This is a Filter Press. Inside the white container is a piece of porous paper called filter paper. Also inside the container is a mud sample. The mud engineer puts the mud sample under 100 pounds per square inch of pressure for 30 minutes. The pressure forces the liquid part of the mud, the filtrate, through the filter paper and into the graduated cylinder. By measuring the amount of the filtrate, the mud engineer can get an indication of the amount of filtrate that will be lost to down hole formations and the amount of solids or wall cake build up on the wall of the hole.

Chloride Test
Mud engineers may run other drilling mud tests. One common test is for salt or chloride in the mud filtrate. By adding Potassium Chromate and other chemicals, the engineer can determine if the hole has penetrated a salt formation. It can also determine whether salt water has entered the well bore, which may be a sign of a kick.