Heello everyone, good morning, good afternoon, and good evening to everyone who's tuning in. On behalf of Pio Petro, Arab Oil and Gas Academy, and SPE Egypt section, I'd like to welcome you to today's session. My name is Shahad Behjit, I'm a third year petroleum engineering student at K&U in Kurdistan, Iraq, and I will be your moderator for today.
Before we start, I'd like to remind you to please drop your questions in the Q&A section below. Please keep the chat box professional and ethical, and please submit your quizzes before the deadline. Now, without further ado, please give a warm welcome to Dr. Mustafa Archi, who will be continuing his course on reservoir characterization, plastics, and carbonates. Dr. Mustafa Archi has 25 years of experience in the petroleum industry. Hee holds a Ph.D. from North Carolina State University in the U.S. and a master and a bachelor degree from Alexandria University.
Early in his career, he joined Alexandria University as an assistant lecturer until he obtained his master degree. Hee also used to teach at community colleges in the United States. Dr. Mustafa Archi held many positions in all aspects of the petroleum industry, and he lived in many countries around the globe.
Dr. Mustafa Archi, thank you for coming, and the mic is yours. Thank you, Shahad. Heello, everybody. And this is the last lecture on the four lectures that we assigned for the reservoir characterization in plastics and carbonates.
And the next one will be the Q&A session. So please pay attention to this one, because I don't think we touched carbonates before. And this lecture will be mainly on carbonates.
As you will see, carbonates is a very different thing than plastics. I'm not sure if in the undergraduate... You guys study anything on carbonates or not, but at least I will give you a glimpse on what is carbonate and what are the challenges in carbonate, why they are different than the plastics and all that kind of stuff. So let me remind you with the contents of the characterization course that we started. Lecture four is actually concentrating on the carbonate reservoirs evaluation from the deposition, porosity, lithology, and saturation point of view.
You heard about the porosity, lithology, and saturation of plastics. When we touch this on carbonates, you will see how different they are. Carbonates is, as they say, always a different animal. You cannot actually start looking at carbonates with the same understanding of plastics, because carbonates is quite different.
So that's why there are courses for carbonates that are already assigned and very deeply involved in carbonate. With that said, let's just start with the carbonate reservoirs. What are the characteristics of carbonate reservoirs? Important facts, as we started talking about it, carbonate reservoirs are extremely different than plastic reservoirs.
Plastic reservoirs talk about grains, talk about porosity between grains only. We talk about some type of secondary porosity, like fractures. It's not as complicated as it is in carbonates.
Carbonates are a different type of... grain structure, we sometimes talk about crystals, something that we don't touch in plastics, it doesn't happen in plastics. So reservoirs are quite different when we talk about carbonate reservoirs.
Second, don't deal with carbonate reservoirs with simplicity, it's very complicated. Even the identification and calculation of simple things in carbonate takes quite of thinking, and you have to be careful when you handle carbonates. It's not as easy and I don't want to say that the plastics are very easy, but if you compare plastics to carbonates, yes, carbonates are much harder in evaluation than plastics. Porosity structure in carbonates drives reservoir properties. So you will see how we link the porosity structure with even the simplest thing, even the depositional environment, even the water saturation calculation.
Even the porosity identification, there are so many models talk about porosity. Started since Archi, everybody knows Archi as the guy who started water saturation. But frankly, Archi is the first one to put even some type of modeling of reservoir porosity.
So Archi is not only involved in plastics, when he studied plastics and he started studying carbonates, he found something different. So he actually put the first model. talking about carbonate structures and carbonate pore structure. So, Archi will actually have the hand on carbonates as well, not only on plastics.
So we will see how this thing progressed with Archi and the other people who came after Archi. So we have multiple porosity types in carbonates. We'll talk about them in details. Primability and fluid saturations controlled by porosity types.
Not only porosity values, but porosity types. Saturation can be calculated with models not really related to any resistivity calculation. You will see this also through the presentation. So what I'm trying to give you from this introduction is when you start talking about carbonates or you had the chance when you graduate or these days working on carbonates, you have to handle it different than you handle in plastics. Evaluation even of logging, we talk about even the simple logging gamma-ray.
We all consider gamma-ray is the basic log. Gamma-ray and carbonate is quite different. When we talk about gamma-ray in carbonates and how we use gamma-ray in carbonates, you will see gamma-ray has a big role in carbonates compared to what we do in plastics. In plastics, we use the gamma-ray for probably identifying maybe hot sand, the sand that has some potassium in it. We use gamma-ray in calculating clay volume.
Gamma-ray in carbonates is much, much more important than the role it plays in plastics because it goes to the fabrics. and looks at the fabrics and how the fabrics are affected by the gamma radiation. So carbonate reservoirs, if we look at this picture, it's a very complicated picture, it looks like a very nice picture anyway, but we need to understand it much more than just being a pretty picture. If you look at the carbonates, as you can see it's right here, carbonate actually has so many wording in this slide. We need to understand every wording in it.
in specific because every one of these words mean a lot in this case. So first of all we have what you call limestone and the second one we call it dolostone. Dolostone or dolomite, just skip it to call it dolostone because that's how we how we refer to it in carbonate reservoirs. So limestone and dolostone and as you can see they separated limestone from dolostone.
They are different. Yes they both are carbonate but they are completely different from each other. Okay so when we talk about a rock that's a limestone and you started working on a rock that's dolomite or dolostone, even the definitions of the basic structures of these rocks are different.
So we pay attention to the separation or the differentiation between the limestone and the dolostone. Both actually are made of fabric. We didn't actually hear the word fabric in plastics.
But in carbonates, we use this word a lot. The fabric is the structure. Heow this rock is structured as a fabric.
You've got the fabric of your clothes. The fabric is different from one fabric to the other fabric. Even in this rock, in the carbonate rock, fabric is very, very important to get to know it.
When we talk about fabric, we also talk about is it grain-dominated or is it mud-dominated? So if you look at the carbonates, because it's mostly offshore depositions, and it requires a lot of energy movement for these grains and this mud, so it actually depends on how they are deposited. So you can see either it's grain dominated by grain or it's mud dominated. Mud is also a big role, similar to the clay that we talked about in class.
So mud here in carbonates represent to some extent what we, I'm just trying to give you some analogy guys to at least to relate between what we study normally in plastics and what the carbonates are. So it's either grain dominated or mud dominated. Also if you look at, if you go down to the dolostone, you can see something called crystal, crystal site.
So in dolostone or dolomite, we talk about crystal. And in limestone, we talk about grain. So we talk about grains or crystals.
I'm not going to go deeper into the crystal structure, but at least you need to know between the limestone and the dolomite, it's actually different even in the fabric itself. Okay? So grain-dominated or mud-dominated, and then you go about crystal structure, right?
When we say grain dominated, mud dominated, we actually divide it into four different, five different categories, actually four different categories and one of them is share. So the first one is absolutely grain dominated. As you can see right here, all the grains here, the grains are much higher, much bigger. We call this grain stock.
and if you for any reason you hit a grain stone in limestone you have the best rock in limestone so the best rock in limestone is what called grain stone then you go to the second category which is called pack stone pack stone is less grain sizes okay and less and and less connectivity so as you can see right here between the grains you can see a little bit of mud okay so the mud started to build up when the mud started to build up the the property and the criteria of the rock starts to deteriorate. So the deterioration goes from grainstone to packstone. So packstone is less quality compared to grainstone.
Why? Because the mud started to come in. So we see a lot of grains but the mud started to come in.
Heere we don't see much of mud at all. Heere you see a lot of muds coming in. We call this packstone. So the packstone is a grain stone with extra mud added to it through the position. Then you go to back stone again, and you can see that back stone is shared between the grain dominated and mud dominated.
So this is transition between the two types of carbonates, grain dominated and mud dominated. They actually a transition. That transition depends on how much of the mud you have.
If it's actually more mud, it's increased the volume of mud. then we go from the grain dominated to mud dominated. So, pack stone share between two. This is the linking in the chain between the grain stone and the mud stone. When the mud increases even more and the grain started to decrease, we call it whack stone.
Whack stone is a very low grade or quality of carbonate in the limestone. And the least quality is called mud stone. Means the mud is dominated.
They are between two edges, grain stone and the other edge is mud stone. The grain stone is the best quality of limestone and the mud stone is the worst quality of limestone. When you say grain and worst from the porosity point of view and from the permeability point of view.
So these two things, these categories, and when you identify these categories, you can actually think quickly how good your porosity, how good your... permeability in the rock that you are handling. So if you get some good news that you have grained stone that's good news.
If it was described as mother stone that's really bad news in carbonate. So these are the categories as divided on based on the rock quality and how good the rock is. Then if you go to the other one it's only crystals. Again it goes with the same definitions but again here you can see more of grains.
but the crystal size is big. Crystal size is less than 100 micrometer. Heere is more than 100, crystal is greater than 100 micrometer.
So that gives you a very good quality. And the crystal size started to go be lower and lower and lower. So this is greater than 100, this is between 100, 20 and 100, this is less than 20. So we can see the degradation of the crystal size, which also affected the quality of your carbonate. So the quality of your carbonate based on the deposition and the fabric of the carbonate. We never talk about like this in any of the classics.
Classics are much easier in their definitions compared to the definition that we just talked about here in carbonate. So as you can see, carbonates, even talking about limestone or dolomite, they are different. One is grain dominated, one also goes with the crystal type of structure.
Crystal size has a big role in it. Grain size has a big role in the carbonates. and the influence of mud controls the quality of your rock in the carbonate reservoir.
So carbonated structure, grains and crystals, grains and limestone, grain dominated or mud dominated, grain dominated like grain stone and peck stone, mud dominated is whack stone and mud stone. So these are the four qualities, is it grain dominated or it's mud dominated. as you saw that the pack stone can actually be a link between both between the grain dominated and the mud dominated. We will talk about the crystal structure which is mainly in dolomitization or I'm sorry in the stone of the dolomite and you can see crystal structure also in crystal sizes controls the dolomite reservoir quality okay.
So this is what we saw from the previous slide and also I just summarized it here in this slide. So you can as you can see We never talk like this when we talk about plastic. Now, when you actually drill anywhere, there is something called mud log.
I don't think I talked about mud log before because I just want to show you when you drill in carbonate, the mud logger, which is a mud logging engineer on the rig, he looks at the cutting that comes out of the drilling and he started to describe this cutting. We call his description mud logging. And actually, if he drills in carbonate, he will use the same terminology that we just talked about. to describe the rock that he sees. For example, here is an example from Egypt, from the Gulf of Suez, where you can see a very nice carbonate section here.
As you can see, let's just see what this guy described. For example, he came to the upper section here and he said it's limestone, but he cannot say limestone and his tops. If he said limestone and his top, that's not a complete description. In the classics, he says sandstone, fine grains, coarse grains, and that's it.
Heere, he has to tell me it's limestone, and he said it's mudstone, wacky stone. So he has to use the description that we use because we need to understand how good the rock is. Hee said this is muddy stone.
Muddy stone means it's a very bad rock. It's dominated by mud. There are no grains. Hee said muddy stone, wacky stone.
When he put muddy stone ahead of wacky stone, it means it's dominated by muddy stone. less whack stone. Whack stone is still a very bad rock.
It's better than muddy stone. It has a little bit of less mud. But my point is, he has to describe the limestone with these kind of details.
Hee cannot say limestone and stops. Like we say, see, this is sandy stone. And we need to ask later on how fine the grains are and that kind of stuff.
But in the limestone, he has to tell me what type of the four types that we know. and limestone how he described this piece of cutting that he looked at. For example, if you go even down, he said here limestone also, he said whack stone and pack stone. So now he is giving me some good news. This is a pack stone.
Pack stone means it's a better quality of limestone. So we actually like to look at these details because in carbonates you have to look at these details because the fabric is very very important. factor when you look at carbonates. So when he talks about chalky, whacky stone, packy stone, we need to understand this, we need to pay attention to this.
It's not as simple as it is in some of the classic buildings. So the first piece of thing that we get from the drilling is the mud logging, where the mud logger describes the cutting coming out of the well, and when he sees carbonates, he will tell me this carbonate is a limestone. and he has to go deeper into this what type of fabric are we looking at are we looking for grain are we looking at grain stone back stone work stone mud stone we need to know that we need to know that very clearly now we talked about gamma ray before but gamma ray has a big role in carbon we will see the role of gamma ray in carbon but before we see the role of gamma ray let me remind you with the gamma ray We actually studied the gamma ray in the webinar when we talked about formation evaluation and we introduced the gamma ray tool as total gamma ray.
Today we'll talk about another tool called spectral gamma ray. I touched base actually on the spectral gamma ray before but I will put in a little bit of details tomorrow today because the reason is it has a big big role in the carbonate evaluation. So gamma ray tool is simply tools, two tools are available. total gamma ray and spectral gamma ray. Total gamma ray gives you the total counts of the gamma ray coming without telling you where it's coming from.
We actually learned that the gamma ray activity in our rocks come from three radioactive elements potassium thorium and uranium. These are the three radioactive elements we see in our clay rocks okay potassium thorium and uranium. The total gamma ray, it just counts everything.
It doesn't tell you where the gamma ray is coming from. The spectral gamma ray has the ability to tell you this gamma ray is coming from potassium, this gamma ray is coming from thorium, this gamma ray is coming from uranium. So it looks at the gamma ray total and also divides the gamma ray into components.
That's the big difference between the total gamma ray and the spectral gamma ray. When you evaluate carbonate rocks, you really need to look at the spectral gamma ray. Spectral gamma ray gives much more information that's required in the evaluation of carbon in carbon-dioxide gamma. So total gamma ray tool is applicable in most of the plastics reservoirs. In some cases, it's actually not enough.
If you have what we call hot sand or potassium-rich sand, that's another subject in plastics. But in carbonates, actually, spectral gamma-ray is really a must in carbonates. Because it goes and looks at the classes of your rock and also looks at the fabrics of your rock.
It provides means to identify carbonate rock type. So let's just look about the, just remind you, refresh your memory about the total gamma ray. It's actually, these are the three sources of radioactivity, potassium, thorium, and uranium.
They emit gamma rays, gamma rays attenuate in the rock. You put a gamma ray detector and you count the gamma ray counts that you have based on the attenuation of these elements. If you count all of them without paying attention to where the gamma ray is coming from, that's a total gamma ray. The spectral gamma ray is similar.
There's nothing different. The only difference is in the detector itself. The detector in the gamma ray, in the spectral gamma ray, has the ability to look at identifying this gamma ray.
It's coming from potassium, coming from uranium, coming from thorium, based on the energy of the gamma ray that the detector reads. Because every one of these gamma rays has certain energy. So it looks at the energy and actually counts the total gamma ray first. Then...
put the HeOHe of gamma ray in its category, either it's coming from potassium or thorium or uranium. Okay, so some same physics like a gamma ray tool, they are that all are presented separate which means the potassium, thorium and uranium are presented separately, so it will give you the amount of potassium. We usually give potassium in percent and we'll give uranium and thorium in part per million because it doesn't require much of the uranium and thorium to get the gamma ray reading.
So potassium, thorium and uranium are measured separately and also presented to you on the logs separately. It will give you the percent of potassium and how much ppm, how much part per million of thorium and uranium in your rock. Based on the difference in gamma ray energy, if you look at this, here is the gamma ray energy of potassium.
Heere is the gamma ray energy of thorium. Heere is the gamma ray energy of uranium. They are different.
So the detector is capable of... differentiating these gamma rays based on their energy. So what they do, they have actually three windows.
Each window will be responsible for certain energy. When the gamma ray comes into this energy window, it's counted to potassium, this is counted to thorium, this is counted to uranium. So this is how the tool actually, or the detector, differentiates between potassium, thorium, and uranium. So there is a tool that's capable. of measuring all these components separate plus adding them together to give you the total gamma ray and not similar to the total gamma rating can there be a very basic question why we use the gamma ray tool total if we have a better tool here well it goes back to cost guys we talk about in our industry we pay a lot of money and at the same time we need to make sure that we run it in economics so if i don't need spectral gamma ray there is no need to pay more money for something i'm not really using it but in carbonates no engineering you really need to use the spectra gamma ray because it has a big role in that okay so gamma ray and carbonate deposition for example will first of all say that potassium and thorium are related to clays and rock fragments so clays and fragments we use the potassium and the thorium okay so rock fragment which is part of what we're going to describe here and also the clay volume normal normally to what we used to do in class okay second uranium released to dollar stone so here is the uranium component here remember in the plastics we didn't use uranium before in the classes in the plastic we used potassium and thorium to identify clay type so from the potassium and sodium we can identify clay types in plastics we do the same thing also here in carbonate but the uranium It's very, very critical in carbonate because it actually points out, do you have a dollar stone or not?
Dolomite has lots of uranium attached to it, so we have uranium would be used for the identification of dollar stones. So this is one of the most important parts. I can differentiate between these two types of rock based on the uranium component. So I need this to tell me if this is a dollar stone or this is a limestone.
There are some other means of doing this, like the photoelectric factor from the density tool, but actually gamma ray can play this role very easily and very straight. So here is the dollar stone here that we can use the uranium to identify this dollar stone. Also, green stone, remember this, we said we have to know what type of fabric we have.
The gamma ray will give you this. Green stone and grain dominated pack stone. So the green stone and the pack stone, or grain dominated, it means it's on the side of the grain dominated.
So grain stone or grain dominated. back stone require high energy in the deposition and hence it will require it will show low gamma rate so if i have green stone or green dominated back stone my gamma ray will read low anyway okay because in the deposition it requires higher energy and higher energy is is inversely proportional to the gamma ray so my gamma ray will read low in this case so one of the things that the geologists use to identify these type of fabrics, grain stone and grain-dominated tack stone, is the gamma ray. And the one who will decide which gamma ray limit I need to use for this differentiation is the geologist. So your work with the geologist is a must in the evaluation of carbonate.
Geologists will have a lot of input in the way you look at your evaluation of carbonate rocks. So grain stone and grain-dominated tack stone. require high current energy and hence it will give you a very much lower gamma-ray split.
Okay, so here are the two things, green stone and green dominated back stone. These are the two things that will show with low gamma-ray counts on the gamma-ray tool. Second, mud stone, which is the second part of the fabric which is now the deterioration of your rock fabric, mud stone and mud dominated back stone. and wacky stone or the bad part or bad part of the of the carbonates of the limestone carbonate are low energy current and hence high energy gamma ray so these two things three things mudstone mud dominated pakistan and wacky stone it will give you a higher value of gamma ray compared to the green stone and the green dominated pakistan so these things so that now you can see the role of the gamma ray quite frankly because it will look at the evaluation of your rock fabric because your rock fabric will control the productivity of your rock and it will give you a lot of information on the flow units that you have in your carbon.
So the other part is mud stone and mud stone and mud dominated deck stone. In this case the three will be showing higher gamma ray compared to the other which is the green stone and pex. We continue on this.
That's the role of the gamma ray. You can see it's a big role for the gamma ray. The gamma ray is not really a simple tool, probably a simple tool in plastics, but it's not in the carbonates. In the carbonates, we need to work with the gamma ray very heavily to really identify what types. So uranium should be subtracted from gamma ray.
Why? When you do your evaluation, you have to subtract the uranium. You don't add the uranium to the total.
So you work with the potassium and the thorium. You have to work with the potassium and the thorium only. Uranium will be used to identify dollar stones. But when you do this identification of high or low, high gamma ray or low gamma ray, not the total gamma ray, it's a potassium thorium gamma ray, not the uranium.
Uranium is used for the dolomite. Very critical to do this. Most of the service companies actually do this for you.
That's why you see the importance of doing this. The service companies, they give you two gamma rays. One called...
Cgr, which is the total gamma ray, one called CGR. The CGR curve that your service company give you this, CGR is the addition of potassium and thorium only. Uranium is not included.
So even the service company, because this is very important to have and very important to know in carbonates, they give you two curves for gamma ray, one called Cgr, which is the total. All of them are added together. and the other one called CGR.
CGR is the only potassium and thorium are added together, because that's the one that you will use to identify your rock fabrics in carbon. You will see these two curves when you run the spectral gamma ray. So all the service companies will give you two curves when you run the spectral gamma ray. They will give you first potassium, thorium, and uranium.
Then they will add them all to give you Cgr. and they will add potassium and thorium to give you CGR, the one that you will use in the identification of fabrics. is the CGR. This is an example to really understand this. We have an example here in carbonate.
Gamma ray is really high, it's hitting even beyond 150 that the API is asking us to use as a scale. It's actually going and it's reversed here. Now we will look at the spectral gamma ray.
Heere is the two curves I was talking about. We have Cgr and we have CGR. The CGR is the blue one.
The Cgr is the green one. And you can see the Cgr is very high in this zone. And the CGR is very low. CGR is only potassium and thorium. Cgr is all of them.
It means potassium, thorium, and uranium. So the difference between this curve and that curve is the uranium component. What is the uranium component related to?
It is to dolostone. So uranium will be related to dolostone. stone.
So I can actually easily say that this zone is a dolomite-dominated zone. When you go deeper here, you don't see much of a difference. Uranium is very, very low, so you're going into the domination of the limestone domination in the lower section. So the first thing I knew or I decided from looking at the SCGR and the CGR, that the upper section is dolomite. Lower section is mainly limestone.
So this is a very important part and you can see here we also looked at potassium by itself, thorium by itself, uranium by itself. Actually showed me that you have a lot of uranium here. You don't have much potassium and thorium.
A lot of uranium means this is a dull stone type type rock. Then you go here with potassium the uranium started to decrease so it means the dolomite started to decrease. and here you end up with the limestone.
If I look at the comparison between this and the components, I can learn a lot of things from this one. So this part is the dolostone, and we'll use that part as the limestone. So this is the dolomite section, and this is the limestone section.
Heere is the potassium and the thorium low, uranium is very high, and we agree that uranium is related to dolostone. Heere is another example where you can see Heere is the again the CGR is the blue one, the Cgr is the red one, you don't see much difference. Okay, so you don't see much really of any type of dolomitization here or dolomite. Okay, so you don't see a dolomite stone here because the CGR is exactly like the Cgr.
This means that the uranium is very weak. Okay, so if you look at the components here again, here are. Heere, if you see a little bit of uranium here, but this is very less, less than even 5 ppm.
So 5 ppm is not really very much in the uranium. And the other one, if you need to, let me go back to the other one just to look at the scale, other one here is from 0 to 20. So the uranium is even higher than 20 ppm. So you don't look at just the peak, look at the value as well. It is even exceeding the 20 ppm. In this example, it was not even 5. like this actually 10 is right here and you can see this zone is about five to six parts per million so it's not really that much and you can see that clearly from the overlaying of the cgr and the scgr not really much of a difference so that's why the component of uranium here is a very low scale so it actually doesn't have much of ppm have only four or five or six ppm not like the other one where the dollar stone was dominant in this piece of rock okay so this one will take you the mix from a limestone and dolomite but with a very very minimum value of dolomite.
So how the geologist will help me in identifying my rock fabrics in carbonate? The geologist has to tell me something very important. Hee looks at the gamma ray and he decides where is the cutoff where I can identify a muddy stone from white stone from green stone. Hee has to tell me. If the gamma ray is less than this, this is the type of rock that you're looking at.
If the gamma ray between this reading and this reading, this is the second rock fabric that you're looking at. For example, if gamma ray, this is just an example, if gamma ray is less than 30, it's grain dominated fabric. So it's a grain stone.
So if it is less than 30 API, we agreed that the grain stone and the pack stone has low gamma ray. So if the gamma ray is less than 30 API, again, 30 api is not an exact number it's just an example so 30 api for example the grain dominated fabric will happen at this greater than 30 api to be a mud dominated so the geologist will tell me this when he examined the core, when he examined the cuttings, he was telling me that use the 30 API, anything below 30 API, that's a grain dominated, anything above 30 API, that's a mud dominated. Okay, so that's something that the geologist will do. Okay, so geologists is a key in this type of evaluation.
Let's continue on the example that we started with, example number one. Let me classify my rock types and fabrics in this example. based on what we learn, but the gamma ray will tell me and the input will come from the geologist.
So, for example, here is my CGR, which is potassium and thorium. We will remove the uranium from it when we talk about the classification of limestone fabrics. The geologist told me that when the CGR is less than 15, it's grain dominated. So he told me that when he examined the core, when he examined the cuttings, he found that if the gamma ray is less than 15, what he found is the green stone will be the dominant one. So what we will do, we will put a 15, line of 15. Anything below, any gamma ray below the 15, I will actually mark this zone as a green stone.
So I put a line here of 15 API. It is from 0 to 100. So this is the 15. I put the 15 API. If the gamma ray is below the 15 API, that's a green stone. So I can identify my green stone based on what the geologist is helping me in the characterization. So the characterization engineer works very closely.
We showed that in the previous lecture, he works very closely with the reservoir engineer. In here, he works very closely with the geologist. So because the characterization engineer is a link between all the inputs that you will get from your reservoir.
So the geologist told me here that if the CGR is less than 15, then the rock is defined as grainy stone. So I put the line and then I define it as anything below the 15. So this zone is grainy stone. This zone is higher than 15, so it's not grainy stone.
I don't have a name for it yet. This one is lower than 15, so it is a grainy stone. So I can see, I can actually mark my grainy stone, and I give it a color.
For example, grainy stone, I give the grainy stone a color red. So I identify the grainy stone. These are the best reservoir quality in my limestone.
So I can identify the best reservoir quality now, because grainy stone is the best reservoir quality in limestone rock. Then he told me that when the CGR is above 15 and below 25, then it's grain dominated. It's not really grain stone. It's still, actually the mud started to build in, but you have a mix between mud and grain, but the grain are dominating.
So it's grain dominated means, for example, 80% grain, 20% mud. That's why we call it grain stone. I'm sorry, grain dominated pack stone. So the grain dominated pack stone is...
a mix between grain and mud with high percent of grain in the fabric structure. So what I will do here, I will put a line. Heere is the line of 20, so here is the 15 and here is the 25. I have 15 and the 25. Anything in between, I have to mark it as grain dominated back stone. For example, this zone here between these two. This zone is between these two and so on.
So I will put my evaluation here as this is the grain dominated back stone so these are the zone that's grain dominated back stone it's also a very good rock quality is not as good as the green stone but still very good because the mud is very very low in the in the fabric structure in this case then he continued to tell me if it's between 25 and 35 it's mud dominated okay it's mud domine now they change the pack stone to be mud dominated so it means there is a deterioration of my fabric structure in carbonate so between 25 and 35 it's mud dominated pack stone so what i will do i'll put the line of the 35 so between 25 and 35 i will identify anything that shows up here as mud dominated pack stone so i give it the color green So this green are the mud dominated peck stones. So actually I have a very good rock in this well because I have very high grain stone. very good grain dominated, very little of mud dominated. Now it's only between 35 and 50, it's a mud stone.
Mud stone is a really bad rock. So this is bad news if I see a lot of it. So I will put the 50 and I say anything between this and this then it would be a mud stone. You see everything is going here at the bottom, you can see just a little bit of... the muddy stone which it means my rock is reliable that reservoir is very good from the fabric structure point of view it's a very good very good rock then he said if it's above 50 that's a clay stone clay like the clay that we use in in our plastic so anything above 50 okay if the gamma ray is less than 50 or or if the gamma ray is more i'm sorry the gamma ray is more than 50 then it's a clay stone Then we actually identified the clay stone, which would be the lower section here.
Hee told me that it's very high gamma ray. Hee told me that the lower section here is mainly mainly clay stone. So I actually identified all my zones. Now I can print all of them in one column, and you can see how complex my structure here.
So that's how I look at my grain, my fabric structure in carbonates, and that's, we have to do this. in every single well because you need to look at how these zones are related in your reservoir as a characterization engineer because you need to look at the best rock quality that you have which mainly the green stone and grain dominated back stone okay so in these two things they will really identify how good your reservoir and uh and how they put the productivity of yours okay so as you can see here gamma we didn't use gamma ray this way in in plastics use the gamma-ray and clastic to calculate clay volume. Minimum gamma-ray, maximum, you go and calculate the clay volume.
That's not the case actually in carbonates. Gamma-ray has a big role in carbonate in identifying our fabric structure between the different fabrics of the lines. So very important, do this analysis on every well to build better reservoir characteristics.
Second, failing to do this will result in bad flow units. you're not going to understand your reservoir very well. Yeah, so it's not really, you're not saying this is limestone, this is limestone, so these are the same. No, limestone can be actually one of five.
Green stone, green dominated, green mud dominated, muddy stone, clay stone. So these things need to be very well identified, because your flow units will be based on this type of identification, and you use the CGR, which is the combination of potassium and thorium. in this type of identification. So you do this for every well because that will actually make a good decision on what are the flowiness that you have in your reservoir. That's from the fabric point of view.
We looked at the fabric and we found that the gamma ray will really help us a lot in identifying the fabric of my carbonate reservoir. Ferocity in carbonates, it's a very complicated issue as it is in the fabric. So the fabric is complicated.
Similarly, the process is complicated. There are so many models actually with the foot, and as I mentioned at the beginning, that Archi was the first one to do so. Archi came up with a certain type of modeling.
It was not the best model, but Archi did this in the 30s, in 1930, which the technology was not very good. So we appreciate what Archi did for sure, because with the limited type of technology he had. he came up with a good description okay but with the with the advancement of technology and we are getting our hands on better technology to understand things better so archie actually came out with his first structure carbonate complex forest structure compared to plastics carbonate poor structure went through multiple development and modeling started by mr archie okay completed by lucia lucia is one of the i can say he is the father of the identification of carbonates.
Hee's a very brilliant carbonate engineer. So he actually did a lot for the evaluation of carbonates. So between Archi and Lucia, lots of people actually went through a lot of description of carbonate rocks, but Archi is the initiator. Lucia, in my opinion, some people may see it different, but I think Lucia did a great job in the identification of the carbonate rocks.
So as you see here, for the four types, We go for intergranular mold, cavernous, forget about this, but you can see Archi in 1952 and I said 30s, sorry, in 1950s. Archi in 1950s came up with his idea. Then Lucia came up with the model in 1983. Choukat and Prey came up with 1970, another identification of modeling. Then Lucia in I think in 1993, he came up with his final model.
Heis final one in 1995. So 1995 came up with his final model for carbonate and that was the model in my opinion the best model that describes. the carbonate reservoir porosity and rock quality of the carbonate. So based on, he actually based his model on two things, geologic rock fabric, the one that we just talked about, and the petrophysical property. So he actually built his model based on his understanding of the fabric of the rock, which is very important in carbonate when we talk about the rock fabric.
Again, let me remind you with the word fabric, it means grainy stone, but back stone which is the grain dominated, mud stone, mud dominated, clay stone, all of this we call them fabrics. So he actually looked at this fabric and how the physical properties linked with the fabrics and he came up with his modeling on that. Hee actually identified two things from the porosity point of view. Hee said interparticle. Interparticle means it's actually porosity that came from the arrangement of the grains, interparticle thing, or the crystals.
okay with the grains or crystals because if you talk about dolomite you talk about crystals you talk about limestone talk about grains and sometimes you talk about crystals as well so enter particles between particles okay or secondary prostate secondary prostate is what you call the bugs actually lucia he said petrophysically petrophysically there is no difference between the between the bugs and the fractures he handled bugs and fractures the same the same in fitment petrophysical properties okay look the same in the structure same physical property but he looked at the bugs and he said either separate or touching what are the bugs bugs are actually pores that created after the position so there is no bugs at the at the deposition frosty at the deposition is the interparticle process after the deposition there'll be some chemical reactions happens in carbonate so in carbonates you can actually do a lot even we do that intentionally when we do acidizing we do some chemical reactions we actually acidize rock okay similarly something happened by nature that creates bug so the grain itself the grain itself will react and it will it will actually create a small hole in it that small hole in the green itself we call it bug so the bug is a small hole in the grain itself or in the shell itself so in this case the bugs are are made after the deposit millions of years after the deposition this is this is this is our type of porosity that that lucia considered and he looked at them either separate or touching because if they are separate then they are not really uh contributing to the flow they are touching they are contributing to the flow so he came up with this his modeling and he based his model on on this okay so intergranular and intercrystalline frosty are similar in physical properties okay so here is remember this is intergranular and this is intercrystal okay so this is intergranian this is intercrystal they are similar in the properties lucia called both are interparticle secondary prosti called in bugs and fractures and in his idea that the fractured cavities are considered bugs so even he considered the fracture as a bug in his modeling okay don't you know don't want to blame the guy in the definition but in the modeling in the physical properties yes bugs acts like like fraction. So Lucia Aquiles actually based on his understanding of porosity, he came up with certain type of permeability relationship and that was really something brilliant. So he came up with permeability relationship based on his definition of porosity.
So what he did, he actually looked at this and he said let's just separate and identify rock types of carbonate based on the grain size. If the grain size is less than 20 micrometers, or between 20 and 100, or between 100 and 500, he calls this class 1, he calls this class 2, and he calls this class 3. Who will decide on these? Class 1, class 2, and class 3? You will use the gamma ray with the help of the geologist to identify your classes. So the classes or the fabrics, let's call it fabrics, the classes or the fabrics...
will be actually identified by the integration between you and the geologist. So the geologist and you will define class one, class two, and class three. If you identify this, then Lucia said you don't actually have a problem in going and calculating permeability. So he gave us a correlation. If you calculate the porosity, which is the interparticle porosity, then the permeability for class one is this relationship.
And by the way, it's a really nice, accurate relationship. I used this relationship for a very long time, and I know it never failed me. Okay, when you compare his relationship.
that he built under the understanding of the rock fabrics and you compare this with the core, they are right on, quite frankly. I never seen a well that I worked on in carbonates that actually failed if you use Lucia's correlations or relationship where the fee is in fraction. Let me give you an example of this. Heere is an example where I have the porosity.
Heere's my porosity from the core. The geologist actually came and he told me this. that part is class two this part is class one based on the gamma ray cuttings from the gamma ray values remember the gamma ray is more than this less than that you will actually classify this on classes and fabrics to identify the upper zone as class two the this zone is class one this zone is class two again and the up the lower one is class three so now we will apply we will use the porosity we will apply this on class two for the upper section then from this point to this point is class one from this depth to this depth is class two and go on then if you really do the calculation apply class one here is a comparison between the the core measure permeability and the permeability calculated by lucia they are really in good agreement and as you can see the his modeling works and works very well for most of the carbonates at least based on my experience and with the carbonates i use lucia lucia's all the time And it really never failed me in any one of the analysis I did in carbon. Now, if I didn't do this, if I didn't classify, here is what you go. That's what you get from any type of relationship other than Lucia.
You get really bad thing. But if you follow Lucia, you really get a very good agreement. So I did this to show you that if you are not following what Lucia actually said, that you have to look at the classes. you have to look at the fabric, you have to look at the grain sizes that you have in your rock.
From the grain sizes, you actually classify the classes. If you do this, you and the geologists work on this very carefully, identify all these classes, then you will be right on the calculations in this case. But if you do it blindly, it's never going to work and you're not going to get any good relationship between prostate and perimetry.
Remember, permeability is very crucial in the in the flow units in your in your reservoir also we came up with water saturation water saturation in carbonates is not as easy as it is in plastics okay it is not easy in plastics add to this it's carbonate so it's it's really very challenging so it is very challenging in carbonate but Lucia also came up with very interesting type of relationship of saturation actually based on classes as well. Hee actually put saturation models for classes. So all his model is based on understanding the fabric of your rock. And that's why he was very successful.
Hee was very successful because he looked at the fabrics and he looked at the petrophysical parameters or the petrophysical properties. Hee combined the fabrics and the petrophysical properties. That's why he came up with, in my opinion, the best...
the best carbonate description and the best carbonate methodology to evaluate the carbonator. So Lucia actually based on the same three classes, he said here is the class one saturation, class two saturation, class three saturation. The beauty about the water saturation from Lucia, there is no resistivity involved, there is no Archi parameters involved, and we all suffer from these these parameters.
A M and N. A, M and N in R shape, these are very highly variable in carbonate. You cannot use a single M value and a single N value in carbonate. As you can see, even limestone, it has five categories. Grain stone, grain-dominated backstone, mud-dominated backstone, then mudstone, then whack stone.
So you have so many variations. for what the same category is called limestone. Under the limestone, you have so many categories. That's why you cannot fix value of M or value of N. That's why if you apply Archi, and I saw many people applying Archi and carbonase, which actually doesn't make any sense, because these are highly variable based on the fabric of the rock.
So Lucia came up with his ideas or his modeling of SW based on porosity and He. He is the height above the free water level. You can actually identify your free water level from your reservoir. Then you get He from the free water level. Once you know He, the distance from the free water level, you use SW equation for Lucia.
Let me apply this. Heere is an example from the Gulf of Suez in Egypt. And you can see here, if you look at the upper section, the upper section is limestone.
the lower section is dolomite so i have limestone on the top i have dolomite at the bottom okay so this means i have actually a complex rock okay so i have limestone and i have dolomite and they are separated here somewhere i just put a sharp separation just for sure to show you guys what's going on there is no sharp separation in nature this way but i just want to show you here is a limestone on the top and here is dolomite at the bottom okay now let me calculate the saturation using Lucia's model and you also calculate the saturation using the R-sheet based model. Rw in this well is 0.29. There is a fixed value of M1.76 and M actually is always lower than one or most of the time lower than two in carbonates.
When you see M is lower than two in carbonates you expect some fractures in the reservoir. So even the M value will point out N is actually taken as 2. So if you do know the parameter RwM and N, and this means I have to fix M for the entire well from the start of my reservoir to the bottom of my reservoir, and that's very risky, okay, because M fixed value for carbonate is a very risky thing, okay, also as N. If you do this and you calculate water saturation, here are the water saturation calculations using R-sheet.
parameters based on the parameters that the oil company actually is using. Now, let's apply this using Lucia's model. Lucia said, well, first of all, we need to identify rock classes.
This is one thing. Is it class one? Is it class two?
Is it class three? So the geologists will help you with this. With the help of the gamma ray, you identify class one, class two, and class three. Then you use actually Lucia's class one and class three. class 2 and class 3. The geologist here identified two classes.
Hee said there is a class 2 and class 3, but there is no class 1. So it's not really a very good rock. It's a second and a third. To have class 2 and class 3, it means the grain sizes are very small, and then your pore size is small, and it will affect your saturation in this case. It requires also He. He is the free water level.
Then if you go there, where is the free water level? When we look at the resistivity, there is a very low resistivity zone here, which is the water zone. So we have an aquifer here at the water zone.
If you look at this here, so this is the free water level at XX40. Just to put the XX just to protect the depths of the oil company. So the free water level is XX40. Then from this point, you can actually know what the height above this free water level. and you use the two classes that the geologists identified, class 2 and class 3, to calculate water saturation.
When you do this, here is the water saturation in red, without any resistivity, without any Rw, without any M, without any N. That's only by the modeling of Lucia. So Lucia is very powerful and you can see here Lucia didn't actually need value for M, didn't need value for N.
Hee didn't need to know RW. All he needs to know is where you are from the free water level and identify your classes based on what the geologist is doing. So he requires knowledge of the reservoir, understanding of the reservoir, not just a blind application of models like blindly apply R-sheep or RW or M or N.
Hee actually asks you to understand your route properly and apply the proper relationship based on the class of your rock so you understood your rock from the class's point of view is it good class or it's a bad class from class one to class three then you use the model that he applied for class one class two and class three and you can see here it is really very good agreement in some of the zones there is a little bit of differences and that's when you see this happens at the transition here between from the limestone to to the dolomite that's the difference that's why because when you do this transition these so many things are happening fractures are happening but no sorry M value is changing, N value is changing, because you're actually changing the characteristics of rocks. So that's why there is a difference here. If you ask me who do you believe, I'm very sure I believe the Luchias model, because that transition in carbonates requires a lot of changes, and fixing the value for M, fixing the value for N, is not a very good idea when you use the water saturation. So in summary, for carbonate SW, If the free water level is known and can define the rock type, then use Lucia. And Lucia model does not require RWM or N.
It requires understanding of your rock, understanding of the fabric of your rock, understanding of the class of your rock. Then you use what Lucia recommended for each class from both the saturation and the permeability. This gives Lucia's model a huge advantage over the resistivity saturation models, which is Arche, Indonesian, Maxman, Smith, the dual water, whatever model you're actually using. In my opinion, Lucia's model is the most suited for carbonates if you actually can identify the classes based on what Lucia requested for defining in his model. Thank you very much.
That would be just an introduction of what are the carbonates, how we handle carbonates, how they are different from plastics, what are the major things that you need to concentrate on and understand of carbonates from the fabric point of view, from the grain point of view, from the structure point of view, classes as Boushehr did, type of porosities that Boushehr actually looked at from the intergranular or from the bugs either either connected bugs or separated bugs all these need to be fully fully understood from the characterization engineer before he starts doing any evaluation in carbonates because if you apply the same thing that you apply in plastics to carbonates believe it or not you will fail you're not going to be able to to really evaluate your carbonate reservoir proper just want to say a few notes on the next session next session will be only questions and answers. What I will cover in the next sessions, I will be covering porosity in gas-bearing reservoirs. Many people are asking about this. We will go and understand what are the methodologies to do to identify porosity in gas reservoirs.
Also, I want to go talk about salt sections, how to identify the salt sections. Also, identify the anhydride section. We need to really find this out.
Heow can we visually, I can very easily pick. salt sections, thick and hydrous sections, how to deal with the gas bearing reservoir, and also many questions came on the very gram. I received actually a lot of emails from you guys, which is a pleasure to talk about very gram. So I'll talk about the very gram processing in some details in the next Q&A session. Okay, thank you very much and I hope you enjoyed the webinar.
If there's any question, I'll be happy to answer that. Yeah, thank you, Dr. Mustafa Archi, for a very informative webinar. I'm sure the audience has benefited greatly from it.
In the meantime, I've collected a few questions for a quick Q&A session. The first question is, could you please talk about the application of neural network in reservoir characterization? Neural network, that's a subject that requires at least 10 lectures.
So I'm not sure if there will be time for this. Let me talk to Dr. Ahmed El-Garhi, and probably we can spare one or two webinars just to talk about the basics of the neural network on reservoir evaluation or characterization. It's a huge subject, and it cannot be actually summarized in a few words.
It's a big thing. it will take time just to talk about this but probably we can arrange for a webinar in the future to talk about the application of Neon or Neutrogen in the data supercar trade. Great.
The second question is, does sequence stratigraphy apply to carbonate rocks? Yes, it does. Yes, it does.
And it's very important. As I said, you can actually call it, it depends from your background. Sequence stratigraphy or rock fabrics or deposition environments, all of, you know, in our industry, we have a big problem, quite frankly.
In our industry, because we have geologists, we have geologists. physicists, we have characterization engineers, we have reservoir engineers, we have so many disciplines. One of the things that I found is that we are not even all talking the same language, even in the basic definition. We are not talking the same language. And that creates a barrier.
From the stratigraphy point of view, and from the fabric point of view, there is a big link between what Lucia was talking about from the fabric, from the... position environment to the statigraphy. That link is there but because we talk different languages we are not talking the same language. So when I say fabrics it's actually a function of the position. When Lucia say classes it's a function of the position because if you look at the classes of Lucia he talks about the the green sites and that goes for the positional environment.
It goes for the stratigraphy. It goes for so many factors that affect the grain sizes. But again, this is really something I found in the industry, as I said.
We talk about the same thing, but because we are from different backgrounds, it doesn't collect properly. So when Lucia talks about fabrics, when Lucia talks about classes, when Lucia talks about grain sizes, he's talking about stratigraphy, he's talking about the... composition of the environment. Yes, he is.
Great. The third question is, why do we need to know the types of limestone when we usually produce from dolomite? We usually produce from dolomite? Yes.
What do you mean we usually? That's a very interesting question. The question says...
Can you repeat the question again? Okay. The question...
question says why do we need to know the types of limestone when we usually produce from dolomite and we never produce from limestone? I'm not going to answer the question but that's that's the wrong question okay and I mean to look at the whole middle east they produce from limestone the whole middle east is from limestone. Dolomite actually sometimes it's the problem because dolomite can be a cement. Actually, there is a process called dolomatization that can hurt your reservoir. Yes, there are dolomite reservoirs that produce it, but that's not true.
I mean, the limestone reservoirs that produce are humongous all over the world. I never heard this type of comment before. Go ahead. Yeah.
Yeah, that's the end of the Q&A section. Thank you again, Dr. Mustafa Archi, for dedicating some time of your surely busy schedule to give this webinar and course in general. Thank you, attendees, for tuning in from all over the world.
Please stay safe, wear a mask, and have a great day. Thank you very much. Talk to you again.
Bye-bye.