Previous Lecture Complete and Continue  

  3. 3D Structure of Shale Rocks Studied by NIST Neutron and X-ray Tomography (NeXT)

Lecture content locked

Enroll in Course to Unlock
If you're already enrolled, you'll need to login.


- [Lecturer] Okay so now we know why neutrons are important and I want to introduce our new technique that's NIST, we knew about the NIST Neutrons X-ray Tomography. The NeXT System to study the core scales through these structures of shale rocks. So a little more from the background introductions, so this is a cartoon for shale rocks that I got from professor Ozkan. And then so you can see this black part is inorganic rock matrix and that they are mostly composed by minerals and then this gray part is the kerogens which is the organic matter in the shale rock. And the kerogen is the main component that stores hydrocarbons and it has a lot of nanopores which is why the sides are red. And also this green part is the natural fractures and we can see that the shale rock is very complicated in the homogeneous system and to study the structures we need to know we need to have a technic to identify pore fractures, organic components, and minerals in the rock. To make things even more complicated, if we want to simulate hydrocarbon flow and hydrocarbon is mostly composed by carbon hydrogens it's hard to detect by x-rays so we need to detect all these different elements and distinguish them so one to count things with you after this talk so that if we come by and x-ray you can do this That is all because x-ray and neutron are sensitive to different elements. So x-ray as I mentioned before is sensitive to the high atomic number elements so it's more sensitive to the mineral and the neutrons are sensitive to the hydrogen so it's more sensitive to organic matters. Therefore, this is a NeXT system fueled by built in BT tubing light station. And here we put our samples here and the neutron beams marked by the red ray and so we have an x-ray tube that generates x-ray perpendicular to the neutron beams and so in this case our sample will rotate 260 degrees and we can detect the 3D structures of these samples All simultaneously by x-ray and neutrons. And simultaneously checking both of them is very important because say that our sample is changing with time and we are studying the dynamic processes we need to do it simultaneously because each time that the structure is totally different and so this system allows to simultaneously doing imagery with both x-ray and neutrons. And this is, if you want to see how yourself fits into the beam line, this is drawn to proportional to the real scale, this guy is 5 feet long and you can see how he's arranged to the instrument. And he holds practice cells that I will introduce later. Okay so this slide shows you how powerful to combine neutrons x-ray together. If you have boy kids in your house then you probably have this hot wheel toy car and this toy car is the picture of the toy car that you can see the outer shells of the toy cars are made by metals and the inside of the cars is made by plastic so plastics basically are very hydrogen rich and we put this cars into the BT tubing line and neutrons BT tubing stations and we are imaging both outer cars. And in the x-ray you can see that we can we are more sensitive to the metal outer parts of the cars and the inside of the cars is basically transparent to the x-ray. On the other hand neutrons is very sensitive to the inner parts, the plastic part of the car. It is transparent to the metal outside part of the cars so by combining these two together you can reconstruct more of the structure with more complete information. This is a little bit of a theoretical background. So if we have a sample which is a homogeneous media and Lambert-Beer Law tells us that if we shoot x-ray inside the radiation bings into the samples the radiation intensity will be attenuated and how much this intensity will be attenuated depends on, two prongs, one is Mu. Mu is attenuation coefficient. It's the intrinsic property of the materials. And also, Mu depends on what radiation you use. So you can see the x-ray and the neutrons they have different processes, interaction processes so the attenuation coefficient is very different in this two radiation beam. And also it depends on the thickness of the sample so however our shale rocks are homogeneous medias so this attenuation coefficient is not a constant anymore instead we need to use attenuation coefficient map and this will influence how the intensity will be attenuated. Therefore, its very natural that we call the attenuation coefficient the most important component inside the shale rocks and this is the chart I prepared I calculate the attenuation coefficient for both x-ray showing blue and the neutrons showing orange and firstly we can see that for hydrogen rich components such as kerogen and water and hydrocarbons such as Pentane they have a very high neutrons attenuation coefficient but they have very low x-ray attenuation coefficient this means that neutrons will be very sensitive to these elements and being attenuated a lot but the x-ray is almost transparent to these elements. There are some minerals such as clay minerals they have certain amount of hydrogens and at the same time they also have high atomic number elements so you can see both of x-ray and the neutrons attenuation coefficients are large and so both the x-ray and the neutrons can be sensitive to these elements. Also there are some elements there are minerals without hydrogen inside and this kind of minerals they have a high atomic number elements therefore they are very sensitive to x-ray but transparent to neutrons. Take home message is that neutrons are very sensitive to hydrogen rich components and x-ray are sensitive to the minerals. So with all the information on hand I use this combine x-ray neutrons imaging technique to study the first ever three shale rocks in the world. I used three rocks, one is Barnett Shale. Barnett Shale plugged parallel to the bedding and I used two Middle East Shale. Shale one and Shale two and this one is plugged parallel to the bedding and the other is perpendicular to the bedding. And all these three samples have one inch diameter rock samples. And therefore we are looking at the core shale samples. This is the first example of the Barnett Shale and this is our imaging slice for x-ray and neutrons. In this slide we can see the bright parts means the highly attenuated regions the white part means the highly attenuated regions and the black part means very transmuted regions. Therefore for x-ray the white part means high atomic number regions and the black part means low atomic number regions and for the neutrons the white part means hydrogen rich regions and the dark part means hydrogen poor regions. And we can see from these samples that the upper layers, that there are layer structures and in x-ray its light and in neutrons it looks dark. So this tell us that this is a mineral. Separate XR results tells us this mineral is fluoroapatite. And also we can see that there are regions that x-ray is black and the neutrons is white it means this is a hydrogen rich area which is the organic regions and we have also the regions that both x-ray and neutrons are dark this means that both x-ray and neutrons are transmitted through this area and these are fractures. And you should be noticing that if x-ray CT is the only major element weight then we cannot distinguish these as fractures and organic part you will think that they are both fractures. So we need neutrons to get more information. And there are regions where both x-ray and neutrons have bright, and we have this bright pocket for both parts and there's heel fractures and examine results tell us that these are full of pyrite. However this is a little bit surprising to us in the beginning because pyrite doesn't have high attenuation coefficient for neutrons and details from SEM results tells us that this area is also full of organic matter. And therefore we can see clearly that this is not the homogeneous right, there's some features inside, it's actually two components mixed together. And so by using a combined x-ray and neutrons we can detect different elements. This is a 3D rendering of the both neutrons x-ray and the neutrons the red parts show the high attenuation regions, the organic regions, the yellow part in x-ray show the mineral regions and if I collected the high attenuation region and combine it together we can put all the information together we can see that there's a pocket, like I said before, there's this pyrite mixed with organic components, and there's a pocket and there's a heel fracture going through the pocket and on the other side of the sample is organic rich areas and within this organic rich area there's more dense layers and according to our bedding direction this layer is actually parallel to the bedding and we can see that the heel fracture was stopped by these organic layers. Let's talk about the second rock Middle East Shale and again we can see the mineral part and organic regions and fractures. Again for x-ray if you only use x-ray CT you cannot distinguish the organic part in the fractures because they look very similar in the x-ray and then you need neutrons as more information and to complete the structures. And interestingly there's a stripe in the x-ray and you don't see this in neutrons because in this data we don't have the sensitivity for that and so we cannot be sure that this is a fracture or organic regions so we will go back to study this but this will be very interesting if this is a fracture as it will be similar to the previous example that the fractures were stopped by these organic layers. Okay so this is a 3D rendering, again you will see again that there's layer structures and according to the bedding this is parallel to the bedding and we also see the dots the green dot points are the minerals. More dispersed into the sample. And the third Middle East Shale and this is minerals and it is anhydrite and organic regions and you can see this organic region is very dense and is a dense layer and we also detect fractures and another kind of minerals. So this sample is very interesting because you can see that there is a very dense organic layer and its surprising us in the beginning. You can see this dense layer across the whole sample this sample again is one inch in diameter so it's a very wide red dense layer and also we see there's these mineral layers mixed with the organic part and that this layer is also parallel to the bedding. So of course that three samples is not enough to say much of statistics but within these three samples we all see these kind of layer structures, especially in the third sample. And these layer structures are parallel to the bedding. If these dense layer is common in the shale this actually has an important impact on the shale rock because this dense layer will influence hydrocarbon flow and hydraulic fracking. And how does this influence the hydrocarbon flow is our future goal to study and so you can imagine that if this is dense layer are kerogen with a lot of nanopores inside then this can be a fast pass for the hydrocarbon flow. On the other hand if this is a nonporous hindrance then this will be a huge barrier for the hydrocarbon flow. And also this dense layer of the organic parts can greatly influence the mechanical property of the rocks. Just want to mention for example this part breaks during the clogging. It's because this is a weak point because this organic layer and the minerals in between have very different mechanical properties so it can become a weak point. And also you remember the first sample had a heel fracture was stopped by this organic layer so that can greatly influence the mechanical properties of the rocks. And I also want to mention that current flow modeling for the shale rock is mostly based on the digital rock reconstructed by SEM result. And this is the picture I got from Professor Piri that they simulate hydrocarbon flow through this rock and this is the pore scale structures on the other hand our x-ray and neutrons imaging results give the core scale structures and this will be very interesting if we used the core scale structure and we use it as an input to hydrocarbon flow modeling in core scale. Then we will gather huge up scaling from at least ten to nine quarter of magnitude. And so we will have a pore scale and core scale then we will have more complete stories of hydrocarbob flow. Also I want to mention that NeXT has desiged a high pressure fills, you can see from the pictures these high pressure shales can simulate the reservoir conditions and high pressure and also if we flow through the hydrocarbon flow and we can see how the hydrocarbon's flow is influence by the flow paths such as fractures and organic matter and this will also be our future study. I want to give an advertisement of one of our co-authors Jacob LaManna and he is instrumenting the neutrons x-ray unit stations and he will give a poster section in AGU. If you got to AGU for meeting be sure to stop by his poster, he is also talking about shale study by this simultaneous neutrons x-ray imaging.