Shale and Mudrock Subtle Differences

Shale and mudrock are often grouped together, but they are actually separate materials. Shale is a subclass of mudrock, which is a part of the sedimentary rock group. It is a mix of flakes of clay — usually made of silicon dioxide, calcium and quartz — and silt-sized material combined with other minerals and elements, such as magnesium and copper. These materials are usually variable depending on where the shale is located. Shale is typically gray, but depending on where it is located, it can also come in a variety of different colors ranging from black to red depending on its chemical composition. The shale sequences are usually quite large and due to the texture and color it is very hard if not impossible to differentiate any layers in the sequences with your naked eye. Therefore, drilling in them and locating zones of interest is very difficult.

 

As a material, shale itself can be used to produce pottery clays, industrial clays and cement. However, it is more commonly known today for its shale gas containing properties and the possibility to extract natural gas from shale rock through the process of fracking, or fracture stimulation process. Developed in the late 1990s, hydraulic fracturing and horizontal drilling have become essential, widely used tools for extracting natural gas and generating more fuel for an energy-hungry market.

 

Shale Gas

Shale gas is natural gas trapped in the dense particles of shale formations and is increasingly becoming a vital resource in the market. The fracking process uses water pressure or other chemicals to create cracks and loosen the rock and shale. The fissures are then held open with small grains of sand or aluminum oxide in order to obtain the gas. The amount of shale gas production in the United States is increasing year by year. It has gone from 1 percent of natural gas production in 2000 to 20 percent in 2010, and is estimated to become 46 percent of the production by 2035, according to the U.S. Energy Information Administration. Fracking is also the process used to produce tight oil, which is oil based from shale that is also considered very important and may be used as an alternative fuel source in the future in lieu of petroleum-based oils.

Hydraulic fracking is a growing business in 19 states and counting, the majority of sites located in the continental U.S. along the Rockies, Gulf Coast and Appalachian basin. However, this process can come with some issues for the drillers, one of which has been the overhydration of the clay and other materials during the process. Fracking has faced some regulatory and public relations difficulties over the years, since if it’s done incorrectly it can cause problems for the environment near the site, whether it’s from the chemicals used to loosen the natural gas from the shale or the unpredictability of the natural gas being harvested after it has been released through the process, which can end up in the air and water supplies. Clay minerals present major problems when trying to deal with fracking due to their fine, compacted particulates that can make it more difficult to determine what process to use in making sure that fracking has the best yield of natural gas.

There are also problems in determining what shale means to people working on a project. Since it can vary from site to site in color and composition, there is a lack of consensus among experts about what is the exact makeup of shale, let alone the method that’s best in order to drill through it. There are very few internationally-accepted reference materials on the subject of analyzing shale and mudrock, and the elemental ranges in them don’t account for geochemical diversity. As a result, the analysis of this material needs to be as specific as possible so that there is an understanding among all parties involved in the process of shale drilling about which method is best in moving forward. And this analysis can only be done on site.

It used to be that a variety of types of analysis were used for mudrock and shale, including wavelength-dispersive x-ray fluorescence, inductively-coupled plasma with mass spectrometry, and instrumental neutron activation analysis. However, it has been energy-dispersive x-ray fluorescence, or XRF, that has proven to be the intersection of most efficient and effective with this specific material. Since it can be used on the cuttings or core directly without any sample preparation, ED XRF has dominated the field when it has come to shale rock analysis which makes it ideal for the fracking Industry.

 

Handheld XRF for Shale and Mudrock

Energy-dispersive XRF analysis takes a closer look at the reservoir quality of mudrock and shale at a site to examine where and how to frack  in order to obtain the natural gas located in the reserve. When looking at oil and gas production, the analysis of shale and mudrock is vital, as it can track the drill stream of the mud and create well logs in order to streamline the process and make sure as much natural gas is harvested from the site as possible. .Due to the fine grain size which results from the pressure and deposit regime, simple EDXRF is ideal and allows direct analysis.

XRF for mudrock and shale is typically done in the field on a drill rig with different cuttings. This can mean either pulling out the core sample for analysis through a tube, or the analysis of drill cuttings recovered from the drill mud to measure the elemental properties of the shale. However, these may not be the most effective methods of analysis when it comes to fracking. When measured on the drill core itself the accuracy can be reduced or layers may be missed due to spot size, distance and the human element absent from the mechanical process. Automated drill core scanning therefore requires the human element to review the data and measurement spots.


Analysis is most accurate when multiple cylindrical core samples of the rock are taken from the site over a large sampling field placed into core sample trays, and then analyzed using a handheld XRF to conduct analysis. With this type of XRF, there is a need for minimal sample preparation and the measurements can be done from a few ppm to 100 percent concentration. Handheld XRF needs a matrix-specific calibration, which has been difficult in the past, but recent developments have made it easier to create a site specific empirical calibration.

Analyzing these samples through handheld XRF offers two major benefits. One is being able to pinpoint different veins of elements through the sample pieces. The second allows the human element to enter into the process and to analyze the piece by sight. When it comes to analysis, it’s more important than ever to make sure that this process is able to be thorough while at the same time portable, time-efficient, and cost-effective.

Elemental calibrations exist for elements that are heavier than sodium, among them barium, nickel, copper and even uranium, all of which can be found in shale depending on the site’s location. Through the analysis of shale, one can infer mineralogy and lithology, characterize the reservoir, and apply chemostratigraphy in order to determine what is necessary to proceed with fracking. XRF data aids in measuring productivity, permeability, fracture population and porosity of the shale found on a fracking site, which determine what minerals are at play. In addition, handheld systems offer the ability to identify chemostratigraphic changes in real time, which means that observers are able to assess the paleo-redox conditions, view the mineralogy and look at geochemical changes as the result of a variety of observations, including stratigraphic and paleoenvironmental observations. These elements analyzed together can help drillers determine the best formula in order to determine how much natural gas is available to be harvested, what type of pressure is needed for the hydraulic fracture, and how much of it is required in order to release the natural gas from the shale.

When you apply XRF analysis to fracking, it helps make exploration and production more efficient for the entire team. When you have the results of the analysis, you know what materials you will be facing in the fracking process, so you are able to determine the obstacles that need to be tackled in order to have the best yield. As with the nature of the material, shale and mudrock are substances that have minimal permeability. It’s in this that XRF operates as a form of X-ray vision when analyzing what to expect from the shale and mudrock that you are working your way through in order to find the best shale gas reserves and mine them at maximal efficiency.

 

Bruker Handheld XRF Analyzers for Shale and Mudrock

The Bruker TRACER family of handheld XRF instruments is a leader in shale and mudrock analysis. With several key features that are purpose-built to ensure the most accurate and efficient analysis of shale, the Bruker TRACER will undoubtedly add to the efficiency and assurance of your natural gas mining operations. Bruker TRACER benefits include:

  • Completely customizable calibration paradigms, so that your data is highly accurate for the specific geochemistry of the site where you are working
  • Knowledgeable science and support staff at Bruker to provide training and help you validate your data
  • Fully portable, rugged field instrument
  • Manual or automated core logging
  • Having an onsite mud-logger allows you to guide rig operations in real time, potentially reducing costs and avoiding errors.


For additional information and to schedule a demonstration or feasibility study, please contact an expert at Bruker today.

More XRF Geochemistry Applications: