Drilling Fluid Properties

The success of a well system can hinge on drilling fluid properties.

By Ron Peterson

Drilling fluid properties have a major impact on the success of our drilling project. Properly designed, monitored, and managed, they can affect the time spent drilling the borehole, the stability of the borehole, and the ease of running casing.

They will also affect the amount of gravel pack and grout required to construct the well as well as the ease of the development and time spent developing the well. All these factors play a major part in the time spent on the project and the ultimate profitability of the job.

This prompts two questions: First: Why should you check the drilling fluid properties? Second, the antithesis: Why don’t you check the drilling fluid properties?

I’ve asked these questions through the years and the responses have included: The testing equipment is too expensive; I don’t have or can’t find the mud testing equipment needed to run the tests; I’m shorthanded; I don’t have time, it’s a waste of time; . . . and many more. You get the picture.

So, let’s discuss drilling fluid properties and let’s start at the beginning. You should know the formations that you will be drilling, the equipment being used, and the limitations of the equipment.

You should know the formations that you will be drilling, the equipment being used, and the limitations of the equipment.

Getting With the Program

You have either designed a drilling fluid program based on previous experience in the area or you have met with your vendor and obtained a drilling fluid program based on the project goals and needs.

You know what the funnel viscosity should be and where to maintain the density or weight as well as the other desired properties.

The drilling fluid properties we are most concerned with are:

• Weight or density
• Marsh funnel viscosity
• Water loss or filtrate
• Filter cake thickness
• pH of the make-up water and the drilling fluid
• Calcium level of the make-up water and the drilling fluid
• Sand content.

Rheology is another drilling fluid property that may be tested by a drilling fluid technologist.

Let’s discuss each of these properties briefly.

Density or mud weight is one of the key properties of a drilling fluid. It is a measure of how heavy the drilling fluid is. It is tested using a mud balance or mud scale (Figure 1).

I highly recommend a mud scale be present on every drilling rig. We will discuss the details of weight or density in more detail in a future column.

Marsh funnel viscosity is often referred to as apparent viscosity or relative viscosity. It simply gives you a good idea of any changes in the fluid that can indicate changes in formations and the need to make other adjustments in your drilling fluid properties.

The viscosity of the drilling fluid is measured using a marsh funnel and a viscosity cup (Figure 2), and a timing device. I highly recommend that every drilling rig have this equipment on it as well.

The marsh funnel has a specifically sized orifice in the bottom of it. Make sure that that orifice is undamaged and clean.

I have often had a driller tell me that his drilling fluid is heavy. Upon questioning him, I find that what he means is that the drilling fluid is thick. Heavy refers to density or weight.

Marsh funnel viscosity, commonly referred to as “vis,” is one of the most frequently used drilling fluid terms. We will have a more in-depth discussion of viscosity in another future column.

Other flow properties can be obtained using a rheometer, which we will discuss in a future column as well.

Water loss and filter cake are determined using a filter press. The pH is measured using litmus paper. Calcium is measured using calcium indicator strips. Sand content is determined using a sand content test kit which includes a specially designed screen with a funnel and a sand content tube.

The testing equipment used in testing drilling fluids is all designed to meet American Petroleum Institute specifications and is available through your drilling fluid vendor.

Checking Up Regularly

Checking the drilling fluid properties on a regular basis will help you know when you have encountered a potential problem zone and may need to take corrective action.

Knowing when to take action and what action to take can save you the time, trouble, and the expense of potential hole problems. Avoiding problems in the first place is almost always easier and less expensive than taking corrective or remedial measures.

You can get training and guidance in proper drilling fluid testing protocol through your drilling fluid vendor.

The drilling industry is one of the most amazing industries I know. Those who make it up are focused on the success of the industry. If you have any concerns or questions on any phase of one of your projects, contact the appropriate vendor to obtain the best information on product application.

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If anyone has a question or subject that they would like to see addressed, please contact me either through NGWA or directly at ron.peterson@mountainland.com.

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Ronald B. Peterson has been involved with the drilling industry for more than 40 years. He previously worked for Baroid Industrial Drilling Products and is now with Mountainland Supply Co., a supply company in Orem, Utah. He served as The Groundwater Foundation’s McEllhiney Lecturer in 2015 and was given NGWA’s most prestigious award, the 2013 Ross L. Oliver Award. He can be reached at ron.peterson@mountainland.com.