Table of Contents
I want to start with a basic introduction with the XRD and XRF technology and how they are similar, and how they differ.
So, what is X-ray fluorescence? Very simply put, X-ray fluorescence uses an excitation source to excite elements, electrons within an atom. This excitation will eject an electron from its orbital and there is a transition at that point from the next orbital and this transition releases an amount of energy. This energy is directly proportional to the amount of that element within your sample. Quantitative element analysis, typically magnesium – uranium, it can measure from the ppm level to percent level for most elements. On this next slide, we’re showing the user interface how the operator sees the data output from the instrument. Consists of a graphic output as you can see, and to the righthand side of the slide it also gives you elemental breakdown, concentration and statistical analysis. So that’s the output for X-ray fluorescence. Typical detection limits are shown on this slide here. Typically, detection limits will vary with simple matrix, but these are some general rules that you can apply.
So now we move to X-ray diffraction. X-ray diffraction is a direct minerology tool. It can offer qualitative mineral phase analysis, rough range concentration-wise, 2% – 100%. Other techniques can calculate or derive minerology, but XRD provides a direct minerology and this means that it identifies and quantifies the minerology directly from the crystal structure of your mineral. Continuing on to the next slide, the output of the analysis gives the user a series of peaks for the diffraction pattern. An example of the diffraction pattern is shown on the slide here. The diffraction pattern is then matched against a database of known compounds. There are probably available databases like AMSCSD that focus on mineralogical compounds, and there are subscription databases that can offer a wider range of organic or inorganic substances.
The distinguishing difference between the two techniques are elemental versus minerology. Both techniques use an X-ray source in detector. Both measure to the response of the X-rays interacting with a substance and both provide measurements to help identify a substance. The difference is that XRF is elemental. So, with an XRF you would be able to analyze and detect iron, regardless of its state. The XRD the same analysis will yield information such as hematite or magnetite shown on the right-hand column. It also can, XRF will give you total elemental calcium, regardless of how it’s structured. XRD can show you the polymorphs, calcium carbonate, calcite versus aragonite versus vaterite. This is the main distinguishing difference between the two techniques.
Many companies are now producing oil and natural gas from shale – a rock composed of mud and tiny fragments of other minerals, including organic materials. Oil from conventional formation is easier to produce because it’s typically trapped in a more permeable reservoir rock which is sandstone or limestone, allow it to flow more freely. Conversely, unconventional reservoirs are characterized by tight formations that trap the hydrocarbon and require stimulation techniques to allow them to flow. Recent advancements and horizontal drilling and hydraulic fracturing have made the production of hydrocarbons from unconventional resources commercially viable.
XRD and XRF are cost-effective powerful methods for exploited rich, but I feel very underappreciated sources of data – the well cuttings. And a quick primer for anyone who’s not familiar, well cuttings, often known as drill cuttings, they are the broken bits of rock and formation removed from a drill bore hole. These cuttings will vary from size and texture, they’ll range from a fine sand to a fine gravel depending on the type of rock being drilled and also the type of drill being used. To prevent the well from being clogged, the cuttings are carried back to the surface with a special fluid which is pumped down the well to keep it clean and also to lubricate the drill bit and to control pressure within the well. The fluid is known as mud because of its appearance and consistency, as the drill bit grinds the rock into the drill cuttings. These cuttings become entrained in the mud flow and are carried at the surface.
On the drilling rigs, the cuttings are separated from the mud on a shaker screen, the mud is recycled to be used again and the cuttings are usually disposed of. Part of a mud logger’s profession and science is capturing samples of these cuttings at very regular, close-spaced intervals. Typically, over the shaker screen that samples of well cuttings are collected and using time-based calculations, the precise depth of the formation the cuttings came from can be calculated.
Finding the sweet spot is important to understanding that not all conventional wells are created equal. Not just as between different plays, but also within individual plays. These reservoirs are heterogenous and outside the sweet spot, oil companies have to drill rock that yields much lower production performance. So, operators are universally in search for that sweet spot which implies the area of formation where the hydrocarbons will best respond to fracture stimulation. And shale reservoirs, that sweet spot we’re talking about are hydrocarbon types, relative brittleness, organic richness, thermal maturity, stratigraphic continuity and of course your minerology. Using X-ray technology, we can now see changes within the rock at the atomic and chemical level. And easily find and quantitate areas of well that has more carbon in it, are more siliceous and changes in the cliff.
The exploitation of shale and unconventional resources presents many challenges for the geoscientist. Deposits have significant variation from one basin to the other, so the key for success for targeting these sweets spots in the reservoir, evaluating the density and the structural orientation of their fracture systems. Shale cliff sweet spots are typically characterized by mid to high kerogen content, lower clay volumes, higher effective porosity, lower water saturation, higher Yung’s modulus and lower poison ratio. Using these properties as a guide, reservoir engineers can define a productive drilling program.
XRD and XRF analysis are well-known techniques to petroleum industry that have been used for a long time in order to obtain reliable quantitative data and to highlight various aspects important to reservoir assessment. High quantitative clay minerals can give a first estimation on porosity and pourability and rock. Also, high amounts of dolomite and hydrated salt may allow first assessment concerning porosity and permeability and your carbonates.
Not only can XRD be descriptions, but data can be charted to discover formation tops, trends and it’s especially important when identifying faults. Most shales are highly laminated; this presents a challenge for traditional analysis as a shallow marine sediment, clay, quartz, feldspar and heavy minerals – they exhibit an ultra to low inter-particle permeability and low to moderate porosity and complex core connectivity. Density plays an important role in analysis, giving disparity between various components. For example, pyrite having high density in a smaller volume and kerogen having in a larger volume percent an indicative by weight. So XRD minerology provides bulk rock mineral weight percentage; clear this does not include kerogen porosity.
Brittleness
Brittleness is the likelihood of fracturing under stress is key. It is directly controlled by minerology and the fabric and texture of the mineral components. Accurate measurements with minerals are imperative to evaluating the relative brittleness through a shell plate which can greatly improve your fracking strategies. XRD and XRF are also used in determining the contribution of clay minerals to the engineering behavior of rocks and soils. Ductile shales are naturally hills, while brittle, silty shales with a quartz fraction is more likely to fracture. Geo-mechanical properties help determine the relative brittleness or the debility providing valuable input into completion and fracture stimulation design. So, your XRF when integrated with your XRD together can definitely help understand the rock strength and potential behavior. Your rock mechanics, [14:13], Young’s modulus as well as understanding the rock fabric can be miles of close correlation of the XRF compounds in elements.
Here I’m going to go over a few terms that describe the types of rocks and indicate oil and gas bearing zones. So, shale – it refers to a sedimentary rock that is predominantly comprised of mud, stones and organic materials. Its low permeability means the hydrocarbons trapped in the shale cannot move easily within the rock except over geologic expanses of time, so millions of years. Shale oil refers to a shale reservoir containing the oil. The oil itself is the same oil found in conventional reservoirs. Likewise, shale gas is also used to identify natural gas residues from the shale reservoirs. There’s no difference between this natural gas and the natural gas produced from conventional reservoirs.
Now, the flip it, oil shale is a term not used in a sense of a reservoir, but to the actual type of sedimentary rock that is organic, rich, fine-grained and contains a solid organic compound, known as kerogen – all oil and gas are ultimately derived from kerogen. Tight oil is a crude oil stored in shale and requires modern drilling and recovering techniques to get it out. A natural gas is also produced from shale deposits. Some of the key minerals and elements that are critical in understanding the unconventional reservoir are minerals that can indicate brittleness such as quartz and carbonates. Trace marker minerals and element boundaries, high trace metal values, especially vanadium, nickel, uranium, molybdenum are all good indicators of organic richness. Minerals and elements associated with natural fractures – a pyrite and manganese can be indicators of oxidation and reduction states during deposition or early digenesis. Clay minerals, especially expandable clays and clays as they related to clay diagenesis.
Tightly steering the drill in the zones of the formation that will result in the best production and the sweet spots and the best part of the play is a very difficult skill, especially considering the bit may be tens of thousands of feet deep in X, Y and Z directions. Geo steering is done with reference to geological markers, such as the top and the bottom of your pay zone and are typically defined using gamma rays. Having XRD and XRF data on site assists to define the zone boundaries to keep that drill in the pay zone.
I’ve got an example of that in the next slide. This slide shows just a few of the broad amount elements that can be monitored using XRF. And whether it’s a particular element or a series of elements or elemental ratios, it’s extremely easy to track and log the changes as you drill. Next slide. For example, back to those trace metals I just – the nickel or the uranium, these are all well-known deep in deposits and conditions that represents a persistent environments, which are very important for the preservation of high amounts of organic matter. These trace metals are often concentrated in the shale. The correlation of elemental XRF with XRD helps also to verify the quantitative mineral interpretation for your clay types.
This next slide, this shows how using your potassium and your uranium and your thorium measurements, you can extrapolate – I like to call it a pseudo-gamma, it overlays and correlates very well with down hole tools. The direct measurement of XRD minerology and elemental XRF from closely-spaced cutting mineral collection while drilling, it provides actually a higher quality and lower risk complement to wireline elemental capture tools. XRD and XRF can be logged at the same rate that matches downhole collection reporting, typical drilling rates. When gamma becomes insignificant or tools fail, knowing the minerology can assist in calling top, recognizing the formation and staying in the pay zone. Backup pseudo gamma is an inexpensive backup tool for not if but when gamma sensors fail. Using XRF to pseudo-gamma log overlay has been very successful in difficult drilling operations such as high pressure, high temperature wells where downhole tools error is common and extremely expensive.
X-ray diffraction provides easy identification of corrosion and scaling products with its on-site corrective actions. It’s very of great use to have this right on-site. Certain clays will swell up in the presence of water. When they flow they can trap up the drill type and block up the hole. Often in this case you want to switch to an oil-based drilling mud. Scaling sea water can combine with certain minerals. For example, your sulfites to form scalable in the formation and in the drill pipe. If you see these minerals, you may know not to use sea water-based drilling mud and to be very cautions of using sea water in your nearby injection wells.
The typical well in North America has between 25-50 fracturing stages or more, costing close to $250k per stage with a typical production rate of only about 2% from these wells. That is a lot of money. What if we could reduce the amount of stages and increase the production from those placements? Placing stages in the most brittle areas of the formation will optimize production from those placements and provides an enormous reduction in cost, increases your production rate and minimizes the environmental impact of fracturing. Understanding the mineral composition of these shale resource plates is particularly important with regards to the completion of your horizontal wells and maximizing that well performance. Steering these horizontal wells on a narrow pay zone returns with a comprehensive understanding of those rock properties is required to avoid geohazards and design effective fracture jobs to stimulate the maximum volume of reservoir and optimize recoverable reserves.
I’m really big on expressing that XRF and XRD at the well site do not replace traditional core analysis laboratories, instead complement them as a screening tool. X-ray measurements on well cuttings are simple tests that look deeper into the rock with more precision than observation alone. It doesn’t replace the human on site because the observations on color, texture, green size are indispensable. XRD and XRF complements the mud logger, offering a precise quantification of the minerals, and that data is logged next to the visual descriptions and engineering data. Meticulous methods for the sample correction and the sample prep are essential. All data is reliant on the human on the shaker screens doing the frequent and accurate sample catching. And the resolution of the logs is often dependent upon how frequently those samples are caught. The more frequently, I mean as close as 5-foot intervals will provide the best resolution unto the log. Reservoir characterization is dependent on experts working knowledge and applied geologic models. XRD and XRF help them provide indicators of geological history, your basing maturity, low grade metamorphism and a characterization of lithologies.
Caving
Caving over the shaker are an operator nightmare. Stress fracture is occurring in the formation adjacent to the borehole produces these cavings that are carried along the surface along with the drill cuttings. They are common when drilling shale sequences and generally fall into one of two categories: there’s blocking cavings that have a blocky appearance. They frequently exhibit microfractures on the surface and then there’s splintery cavings. These are very distinctive, being elongated and flat with a concave cross-section. An abundance of cavings of this type are strongly indicative of borehole instability caused by underbalanced drilling. The differential pressure allows swelling of the formation adjacent to the borehole and therefore the purity of the splinter cavings is often associated with other indications of borehole instability, such as an abrasive torque and overpull and drag while tripping. One of the greatest challenges is trying to determine where down the borehole these cavings came from. One great benefit having XRD and XRF on site is that when problems arise while drilling, such as well bore instability and fluid losses, if the pilot hole wall cuttings were logged, you have an XRD XRF fingerprinted well and the subsequent cavings can be immediately identified to pinpoint the exact location of the losses.
What we are looking at here is a typical log that incorporates mud logging and engineering drilling and MWD gamma data sets. But what’s extra on here, these are the arrows pointing to is a track with XRD information. You can see some arrows pointing to shill which was the visual topology and I saw these cuttings for myself, that’s exactly what they look like. Even under a microscope, they are very, very homogenous. But once we were able to run the field XRD on them, now we can see vivid differences in that kind of visually homogenous shill. With clarity you can see areas that have more carbon in them, are more solicitous and places and changes in the clay. Now, more on the spreadsheet level, the trace and the marker minerals have a myriad of applications and exploration and reservoir characterization.
So not only can the well cuttings and shills kind of look the same, but gamma and sensitivity tools are often not sufficient to recognize tough steering situations such as lateral facing variations. A dip change in fault throws. Especially XRF data can help here. With that widespread elemental data from magnesium to uranium that can be obtained down hole from the well cuttings and often 30 minutes or less along with a large set of elemental ratios, you can quickly gain a very comprehensive understanding of your position down hole.
So once we have collected her samples and introduced them into the instrument, run the analysis, our software program has the ability to provide a comparison plot of multiple samples, which is extremely useful when looking for trends and more importantly anomalies in those trends that you’re looking for. The waterfall plot allows you easily visualize the changes in minerology by the appearance or disappearance of peaks over the drilling depths as the example shown here circled in the waterfall plot.
Picking out two of the diffraction patters from that waterfall plot, we can look more closely at certain depths to see the changes in minerology. Here we can see the change in composition from 2600ft. to 6200ft. The changes are labeled accordingly. Once again, picking out two more patterns from the waterfall plot we can see that even in as little as 400 feet, we can see the changes occurring. In this case, we can see where chlorite peaks disappear and illite starts to appear. Again, shown in the diffraction patterns.
Speed of analysis and appropriateness of analysis length is always important. Our XRD systems use a CCD detector or camera which captures the entire two fader range simultaneously. This allows the user to start seeing the pattern almost immediately, which is important when fast results are needed. As it continues to collect exposures, the signal to noise ration improves and you can decide when the results have shown what you need. Our customers are doing typically 5-10-minute tests. Of course, depending on how much they care about quantification of the secondary piece.
Once the analysis is done, quantification using relative intensity ratio is then done. We do a quick semi-quant using XPowder and we can set up a few patterns and turned into a push-button operation. We can select the phases visually from a small database and we can set up reference files for future quantification of similar matrices. What this allows you to do is go through the identification process automatically instead of one by one.
Many questions about accuracy, about comparison of field versus laboratory XRD. Most people wonder about how well the field XRD compares to the traditional lab-based instruments. This was a study from a drilling company where we compared the results from our Terra to a full-scale laboratory instrument. As you can see the results showed very good correlation throughout.
XRF output can be both graphical or numerical. So, what you are seeing right here is a comparison as Dawn talked about of elemental concentration versus depth. This is a small subset of the testing that we ran, but it shows very clearly and easy readout of XRF results. And typically, this is what operators are mostly looking for, just a quick analog.
So not only do the Olympus XRD and XRF instruments provide fast analysis, but having them on-site eliminates the time involved to send samples to an outside laboratory. This puts the information in the operator’s hands almost immediately, allowing them to make decisions in real-time. As you can see from the examples we’ve given through this presentation, there are many benefits for having these benefits in the well-logging trailer as part of a routine analysis. They can provide more detailed information that was possible in the past; they can provide backup information and verification to other analysis tools such as Dawn mentioned. They can provide data that can optimize operations and better understand what’s going on underground.
Q & A
Are your instruments able to be used – oh, I’m sorry – are all of your instruments able to be used in the field? Yes, we have 3 different XRD units, they’re all for different levels of field portability. The TERRA is fully field portable XRD unit; it’s built in a Pelican field case and be run on batteries. So it’s designed to be taken anywhere that you need it. The batteries can help with power fluctuations that can happen at remote locations, and the filter also helps to minimize dust.
On the other hand, the BTX-II is a small benchtop XRD unit. It’s small and lightweight enough to be moved around, but it is not designed to be as durable and rugged as the TERRA. This unit can run on outlet power and doesn’t require extra cooling. The Profiler is also a small benchtop with XRD and XRF capability. It also runs on regular power. It’s small and light enough to be moved quickly and easily. For the XRF, the X5000 is just like a TERRA; it’s a true field portable instrument that can run on batteries and is also built into a durable field case. And by the way, it also has a computer built in.
Can the instruments handle external temperature variations? Yes, the instruments, all of our instruments have a cooling fan that takes care of any electronic needs, such as circuit boards, etcetera. The detectors themselves have a Peltier cooler which is independent of that cooling fan. So ambient variations should not bother the instruments at all. Did you use RIR standard database? Or did you determine your own RIR? I’m sorry, we do use RIR but I don’t really understand the question. Maybe you could be resubmitted.
Do you need to use multiple XRF calibration models to ensure optimal performance, especially in challenging and light element analysis? No. Not with our instrumentation. We developed a very specific XRF software called Geo Cam. Geo Cam in combination with a rhodium X-ray tube for the instrument will handle large variations in both concentration and Z weight of your sample. So essentially the Geo Cam calibration can take you from low ppm to 100% without changing calibrations. It’s a very robust calibration and no, you do not need multiple XRF calibration models.
Yes, we have another one coming in. How do we get standards to build calibration in XRF? Well, as a company we’re not a standards provider, reference – certified reference material. There is NIST, ASTM, US GS just to mention a few if you go to those websites. They have many, many standards that will suit your exact needs with certificates of analysis and everything that you need.
Field XRD and XRF, it’s not only ideal to make fast drilling and geo steering decisions in the real time, it’s also cost-saving screening methods to reduce the amount of samples you may have to actually send into a lab. A lot of times when you’re sending enormous amounts of samples into the lab, it takes an enormous amount of time to take them back and sometimes you really need some information in some specific place. So you can get through a lot of samples at a reduced cost and traditional XRD labs are absolutely necessary for certain applications. They’re absolutely necessary for studying true [39:12] and measuring clay expandability. Field XRD will quantitate the amounts of particular clay minerals, but if you have samples you’re especially interested in, especially with their discrete clay properties, this is a great opportunity just to go through the bulkier well and take those and send those to a traditional core analysis laboratory and also get your results back from them a lot faster.
Can you speak a little about sample preparation for mud logging? What protocol do you need? What do you need? Electric grinder or manual? Again, sorry for my hesitation. These are coming in live. So I’ll take – this is really a two-part question. I’ll take the first part in regards to sample requirements or instrument requirements. For the instrument, we supply a manual crusher with our instruments, along with a 120-mesh sieve of simply grind, sieve, low to small amount of powdered sample into the sample cell. And in the case of the TERRA and the BTX-II they use about 15 milligrams of sample, that’s about it. For the Profiler you would load 25 milligrams into the sample cell for XRF; the X5000 requires minimal sample prep. I’d also like Dawn address from the mud logger’s point of view what simple preparations requirements are.
A question I get all the time is how are you representing thousands of feet or an enormous amount of rock with such a tiny little sample that goes into the XRD? And the real key for this, although the machine does require just a tiny bit of powder in order to operate, the bigger you initial sample is going to best represent what’s going on down hole, and then split that evenly down so that you have the best chance of representing the minerals in the interval that you’re interested in studying. The secret sauce to accurate, repeatable and useful XRD and XRF is always in the sample prep. And this begins with the human factor: accurate sample catching and recording of the inventory is essential. Your next thing that’s important is cleaning the sample. Depending on the type of drilling muds, if you have water or oil-based or synthetic oils, the right solvents, the right surfactants, the right cleaning solutions need to be chosen. I can’t definitely give an answer for the right solvent or the right cleaner for every single drilling mud, because they’re all unique. But if you want to email more of these questions, I can answer and give you recommendations for different choices for cleaning your samples in different types of drilling muds. It’s really important that you don’t destroy the really fragile minerals that are in place that are inside your sample. It’s best to air dry your sample, low temperatures. When you’re crushing it’s dust done by hand. Although some of these minerals seem really robust, you can actually break them down pretty quickly so the sample prep is the most critical part of a great diffractogram later. With the TERRA you absolutely have to get the particle size down to less than 150 microns in order to enter but luckily I haven’t met a rock yet that won’t get down to that size. Once you got a nice dry powder and great homogenization and you really are set up to have a beautiful diffractogram with the TERRA.
How long does the whole sample prep take from shaker to instrument?
If you have it down to kind of a systematic approach, without much effort or killing yourself it’s pretty easy to collect, clean, dry, grind and run the sample and get results in 30 minutes. And even your MWD tools are typically about 60 feet behind the bit when they’re gathering information. Most drilling arrays honestly running the sample and XRD and XRF every 30 minutes keeps you in a similar zone as even the MWD tools do down hall.
The next one is really a two-part question, so I’ll answer the first part really quickly. Can you use Ritvelt analysis with your instruments? Yes, our data output is accepted by all Ritvelt refinement packages available in the market today. And the second part of the question is do you think that there’s an advantage to use Ritvelt method with the data quality provided by the instrument after 10 minute acquisition? Well, the use of Ritvelt differs from company to company. Some use it and some don’t. Ritvelt is comparable with our instruments and software and we sell a Ritvelt program called Cirquand. But there are many others that can be used also. We’ve done studies that compare our results with Ritvelt results and it’s shown very good correlation. So it’s just a matter of preference and what engineers need. So it depends on your needs and it depends on the level of analysis that you’re looking for.
Are portable instruments less accurate than laboratory instruments? Quick answer: they are just as accurate. And on one of the slides going back showing data correlation between lab instruments and TERRA field portable showed excellent correlation. Now, when used properly our instruments will give data very comparable to a much larger laboratory form models. One more? Yeah, this one is really for Dawn. Do the types of additives used in drilling cause erroneous readings for XRF and XRD?
Typically, they do not because after we clean them off, what we’re studying as a mud logger is what’s inside of the rock, not what’s coating it on the outside and because of the drilling fluids and the muds we use it absolutely has to be clean in order to study the formation. So kind of breaking the egg open, after we get all the gunk off the outside, then we can discover the properties of the formations in spite of those cuttings by breaking them down.