good day to all of our petroleum industry colleagues i hope everyone is safe and sound my name is luma almana i am a petroleum engineer currently working with halliburton iraq as a field engineer mlwd on behalf of arab oil and gas academy i would like to welcome you all to our virtual q a session for the pre-giving course reservoir characterizations classics and carbonates given by the remarkable speaker dictor mustafa araravi viktor mustafa has 25 years of experience in the industry he got his bachelor and master's degree from alexandria university he held his phd from north carolina state university he worked as an assistant lecturer at alexandria university before he got his master's degree he also used to teach at community college in the united states industry-wise he held many positions in all aspects of the petroleum industry and located in different countries hello everyone i hope all of you are doing great and staying safe my name is selma rashidi i'm a petroleum engineer i owned my bachelor's degree from the american university of los alamos as mentioned before our lecture today will be delivered by the master of simplifying the petroleum technical knowledge and our lecture today will be delivered by uh will be delivered by dr mustafa and the lecture will be divided into two parts the first part is addressing the major questions uh which are a porosity and gas bearing reservoirs identification of salt and anhydride beds from logs and multi-variogram processing hi everyone good morning good afternoon and good evening my name is asmashidi i'm a petroleum engineer who recently graduated from american university of brussels before we start i would like to remind you that if it's the q a session so please if you have any extra questions please drop them in the q and a box so please pay attention and welcome dr mustafa dr mustafa the mic is yours thank you very much thank you luma uh salma and asthma uh as you guys here we have actually the q a sessions and it's divided into two major parts the first one is the one addressing the questions that i use to receive from you through discussion uh sending emails to me and also putting these questions in some of the panels i will address the these questions the variogram was actually asked by so many of you so that's going to spend some time on talking about the program processing and how is it different from the histogram that we discussed before we touched base before on the very gram and we said the program processing is more difficult and it takes in consideration other things that the histogram doesn't at the same time there were other questions regarding the porosity and the gas bearing reservoirs uh how the how the gas would affect the porosity how the log will look like especially on the separation between some of the logs uh also the through the uh the carbonite session uh we always face the anhydride beds and the salt beds how can we identify those uh from logs very quickly so we'll discuss these three major questions that i used to receive from multiple of you guys the second part as asthma actually said i will also give some time for other questions that may relate to the subject or anything that comes to your mind related to the reservoir characterization just to uh you know ask you tweets discrete and you know don't make it generic questions because i receive some generic questions that requires actually more than one or two or maybe three lectures to add these these questions understand that you guys like to get more information about things but you know sometimes the time limit uh will put us in a very limited position to answer your questions okay so let me start with the uh you know an overview of what we decided to do in this in this course we had actually four lectures before and today would be the lecture that we uh we discussed some of the questions that came to your mind okay so the first question porosity evaluation in gas reservoirs uh to answer that question actually i need to make a very quick review on some of the webinars that we discussed already before especially the webinar that we discussed through the formation evaluation uh course that was in the in the summer uh when we started talk uh doing the uh the training and also uh on the second lecture in the characterization just a very quick review to remind you of some of the characteristics of some of the logs and how these characteristics will be changed due to the gas existence and the reservoir actually when i talk about gas this you may differentiate between gas bearing reservoir which means gas reservoirs or gas actually that comes also in the reservoir after uh being produced because everybody know that we have something called the bubble point bubble point is a pressure point where if your reservoir is an oil reservoir for example and you started producing it the pressure will decrease then there is a certain pressure where the bubble points when the gas starts to build up so in this case you will be having three phases the water and the gas and oil and the gas yeah so also the some of the wells that you drill or you evaluate after your reservoir reaches pressure below the bubble point you will also see these type of effects okay so the existence of gas will have some uh i can say signatures on the logs that will help you out identify the process okay so first of all the composition flows in pores in general we touched based on this before and we said actually if you look at any reservoir in the pores that we are interested in what do you find you find two major fluids water and oil and gas okay or both actually so it can be water oil and gas at the same time when you look at the water composition versus the hydrocarbon composition water is h2o and hydrocarbon is hydrocarbons it's actually hydrogen and carbon water is hydrogen and oxygen so actually this is a very important thing we found out from just looking at the chemical composition of these fluids that the water has hydrogen oil and gas they also have hydrogen and the the neutron tool took advantage of this the advantage is that these fluids all these flares they have hydrogen in it regardless what the fluid is the original warsaw that was there before the migration of the hydrocarbon and then the hydrocarbons they all have have hydrogen so the the people took advantage of having hydrogen in all the close components and they decided to design a tool that actually measures the hydrogen component and then they will relate the hydrogen to the porosity where they were the hydrocarbon and the water level okay so that was the basic idea that we discussed it in details in the formation evaluation also we touch base on this on the second webinar of the characterization so hydrogen is the component that's shared between all the fluids that we have in the reservoir so if you measure hydrogen atoms this can be translated to porosity and that's all the main the whole thing about about the neutron okay so if i look at the neutron tool it's mainly a neutron source and this neutron source emits a high energy neutrons which go into the formation and started to do some collisions with all the particles in there or all the atoms in there that way probably with the collision of all the atoms they lose energy and we found out that the one that has the most effective collision on the neutrons is the hydrogen a single collision can actually cause the the neutron to lose all its energy the only uh atom that can do this is the hydrogen so hydrogen is the most effective of slowing down the neutrons from being high energy neutrons to low energy so we took this this criteria and we designed this tool accordingly so you send the neutrons all the way they actually make all collision and they can see it emits a very high energy neutron and then all neutron colloids with hydrogen and other elements but the most effective element is the hydrogen the reason is its mass is very close to the neutral mass and then hence they have the same mass then they'll be very effective in slowing down the neutrons then we put actually two detectors near the electron nfr detector and we actually looked at why we have two detectors that's a compensation for the whole board and also that was discussed in the formation evaluation webinar so actually if we need to get into more depth and why we're having this design while we're having these two detectors as i said it's actually covered in the previous workouts okay so the neutrons come out uh they make collisions with all these atoms and then slows down and then go to a near detector and far detector we take a ratio between the new detector counts and the far detector counts and from this ratio we translate it to porosity but the most important part is and that's what we really need to pay attention to if you have less hydrogen you have low porosity okay just pay attention to this if you have less hydrogen then you have low porosity and if you have more hydrogen then you have high porosity okay so that's how the tool actually translates the counts into into porosity and if you have very low number of hydrogen then you don't have much of porosity because the hydrogen lives in the pores okay so less hydrogen means low porosity more hydrogen means high pros keep this in mind but this is this is very very critical also i i hear you that highlighted these two things again i'm repeating myself more and more less hydrogen means low porosity okay just keep this in mind now let's assume that i'm having a structure that we also covered in the second webinar in the characterization where i have multiple layers here of different lithology we have clay we have sand lime and dolomite okay and that's this is the structure that contains the majority of the lithology that we deal with and the majority of the reservoir that we deal with we actually face clay beds then we have sand or some reservoirs and we have carbonates either being a dog a limestone car carbonate or a dolomite okay now let's assume that my reservoir has a 20 pu but this one has 20 pu and this one has 20pu and this one has 20p when we actually looked at how the neutron tool will react to this and how the gamma-ray tool will react to this well the gamma-ray first of all it will see the clay and clay has a property of having high gamma ray uh measurement so the gamma ray will read high in front of the clay but since the sand lime and dolomite are reservoirs reservoirs has a characteristic of having low gamma ray okay why because it doesn't have much of clay as the clay beds if your reservoir has very high clay content that's a bad reservoir okay why because that layer will live in the pores and then your effective porosity will be very low also we talked about the effective porosity previously and the effective prostate is what we call clay corrected for us so you can have 20 pu but if clays live in the 20 pu it can reduce it to 5 then you lost your frost okay so the assumption that what the reservoirs that we have here are clean reservoirs and we don't have much of clay okay so in this case here is my 20. how how the the neutron tool will act to this and how the gamma ray tool will act first of all if i am in an oil reservoir and keep this in mind if i have an oil reservoir we discussed this in the in the previous webinar here is my gamma ray gamma ray will read high in front of my claim and it will read law in front of my reservoir okay this low means doesn't have to be that much low low means slower than the clay to put it that way so it's slower than the clay because it's not a clay bit it's a reservoir for the neutron tool and since the api asked us to put this on a limestone scale and that's why you have this one from negative 15 to 45 we talked about this so many times then we found that the clay will read very high porosity the reason is all clays they have hydrogen in their composition and since the neutron to reacts to how much hydrogen do you have then i will have actually a high reading in front of the clay is this real porosity no because we know that clays are not really a reservoir and doesn't have porosity that the hydrocarbon can live in okay so in this case we will see high porosity but we know that the high porosity is not real yeah but it's only coming because clays we have a lot of hydrogen in there so that actually reflects how the neutron tool reacts the neutron tool reacts nearly to the hydrogen component in anything in clay we have hydrogen component then the clay will read high process in the reservoir we have hydrogen components coming from water and coming from hydrocarbon so it will also give us some good thrust so in this case we'll see the first thing in front of the clay you will see the neutron will read high pressure yeah high porosity and in the order of the left side of the uh of the 20 because it could be higher crust now when we put the sandstone on the limestone scale we found that the sandstone will read lower porosity than 20 because we're putting sand on the limestone scale again we discussed this in details in the second webinar in the characterization please go back and and review this we will discuss it in details there so in in the sand in front of the sand you will see that the neutron tool will read less actually it will reach 16.5 if it's 20 pu okay so to read 16.5 since then you put sandstone on limestone scale we always say wrong blithology on wrong scale it will give you a deviation from here from reality since the sandy stone is the wrong score wrong mythology on the wrong scale the scale is limestone so putting sandstone and limestone then your frost will get affected so the sand will read about 16 and a half pu in in this zone one in the second one which is a limestone now limestone and limestone so it's the right porosity on the right scale so there is no need for any differences so on the limestone only you will see the la then the neutron tool will read exactly 20 because the right lithology on the right scale the lithology is limestone and the scale is limestone so it will read exactly to an ep okay there is no reason not to read different when you go to the dolomite it's another different or wrong lithology on the wrong scale it's a dolomite on a limestone okay so in this case you will see to read higher porosity than the 20 to be 27.5 so in front of the sand it reads lower okay so the sand on the limestone scale it will read lower the lime on the limestone scale will be exact dolomite on the limestone scale will be higher okay right then we started looking at the density how the density will react to this okay so in in just okay pay attention to this as well now if i am in a gas reservoir what's the difference between the gas reservoir in this case and the oil reservoir the number of hydrogen atoms in gas is less than the number of hydrogen atoms in oil and the number of atoms of water so gas will have less number of hydrogen than oil and then water okay so what do you expect in this case the reason is less hydrogen it will give me lower frost we agreed on this if i have less hydrogen i will get low process so this means the neutron tool will read lower porosity in gas reservoirs the reason is very simple guess we have low number of hydrogen components compared to oil and water so in gas reservoir expect your neutron tool will read very low process okay so just keep this in mind from the understanding of how the tool works the tool works on measuring number of hydrogen since the hydrogen in the gas is less than the hydrogen in the water and the hydrogen in the oil then in this case the porosity in the neutron porosity in in any gas reservoir it will be it will need low so this means neutral log in gas reservoir what will be the behavior first of all this one the clay will stay the same because gas is not going to live in the glacier gas will live in my reservoir okay so gasoline is not going to be in the clay so the clay will not will never change it would be the same okay how about the the the sand we said if the sand has gas in it that even low process will be even much lower so you're expecting it to need much lower porosity than even the original one the original one was low because it was sand on limestone escape now if there is gas in the sand and since gas has much lower density a much lower hydrogen than the neutron and then the oil and the water then it will read lower than oil and water okay again for the lime stone scale it will be the same if my lime 20 gpu don't have oil or water it has gas in it then it will read lower porosity so this one will be less than the 16 and a half that we had originally this one would be less than 20. so what the gas will do to your limestone in this case if my limestone 20 pu now is charged with gas not with water or oil it will read less porosity so gas will actually make the neutron to read less porosity than it should and the reason is gas has less hydrogen component compared to water and oil similarly in the dolomite it will read less since this is the high side of the of the neutron so needing less it will come up at this point so it will be reading less than it should so that's the effect of the gas on my neutron why i can i see less frosty than normal because gas has less hydrogen component compared to oil and water and since the neutron tool reacts to the hydrogen component in your rod then it will be very highly affected so i see even lower frosting than than the normal sand and lime in on limestone lower porosity and on the limestone formation and lower prosthetic lumbar information as well okay so that's the first thing first thing is my neutron tool will read lower porosity than it should and if my reservoir has gas in it okay the reason is gas has less hydrogen compared to both water and fire all right now let's just go to the density because we always combine neutron and density on the same track so how the density will react to this well if you look at this it measures also bulk density so the density tool measures bulk density now the question is bulk density is used to calculate density processor that's what we do we take the bulk density and we calculate density prostate how do we calculate density density is row matrix minus rho bulk divided by row matrix minus row fluid since we put the neutron and the density on the same scale and we discussed this in details before then i have no choice about the row matrix okay we put both of them on the same scale on the same track that the scale of the line of the neutron is limestone scale then i have to use the limestone density for the density prostate okay to be consistent because the neutron and the density are plotted on the same track okay if they are plotted on the same track then they have to be consistent in the scale since the api is asking us to put these logs on limestone scale since the neutron includes raw matrix then the roommate and the density process includes draw matrix then i have to put the aromatics as the density of the limestone in my mind vd will be 2.71 divided by row matrix is also 2.71 about the roof load the roof load is the calibration flow the calibration fluid is the water then the density of the water is one so the density process will be 2.71 minus rho divided by 27.71 minus minus 1. if i need if i go there and i see how the density will react in the oil okay then if i look at the density of the 20 pu density of the 20 pu is 2.32 the density of the 20 pu limestone is ok hold on a second the density of the 20 to 20 pu sandstone is 2.32 now let's you use the density here and calculate the density frosting of the sand okay density process is vd row matrix minus rho bulk divided by row fluid minus 1 which is 2.71 minus 1 and in this case if i put this it will give me a velocity of 22.2 22.2 is higher than 20. 22.2 is higher than 20. so what is the density positive will be here is my 20. so the density possibly on the other side and that's why when you draw the density across you see certain type of separation density to the left neutron to the right that's separation we call it the sandy stone separation we are in an oil reservoir okay now what is the density of the limestone 2.368 go for the density porosity here it will be row matrix which is 2.71 minus rho bulk which is 2.368 divided by row matrix 2.71 minus rho play with which is one if i do this calculation i will get exactly 20. why because it is limestone on limestone escape limestone or limestone scale there is no reason to to be different so it will be reading exactly 20. so the neutron and the density will overlay only in front of the limestone the reason is i'm using the limestone scale and limestones limestone lithology on limestone scale there is no need for for any differences now if i go to the golomite dolomite 20 dolomite is 2.496 gram per cc if i take this and you plug it into the density equation the density across the equation then your your process will be 12.5 12.5 is less than 20. okay so then you'll be seeing the density is actually going on the other direction so we say that in front of the sand i see the neutral density will separate where density is to the left neutron to the right in front of the lime they will overlay because it's a limestone on limestone in front of the dhulam you will separate but opposite to the sand where my the neutron is to the left my density is to the right now it is actually the same kind of separation with the clay now how can i differentiate between the clay and the dolomite we said in front of clay i have to see the gamma ray reading high so when i see this separation that the neutron to left density to the right then in this case i have to check with my gamma ray if my gamma ray is high i would call it clay if my gamma ray is low i will call it dolomite so the dolomite and that lady share the same type of separation but the judge is it clay or is it dolomite the gamma ray would do that for me okay so this is how the neutron density will react in front of and over in the case of oil reservoirs now how about the gas on the on the density well density of gas is less than density of oil and density of water so this will make that the bulk will be actually if the bulk was 2.32 in the case of oil then it would be less because it's now full of gas and also the density of 2.368 it will be less because my limestone is full of gas and the 2.496 my density will be less because my reservoir now is full of gas so the gas will make my density less if i go and out and try to calculate my density prostate in case of gas reservoir here are my equations i'm saying raw matrix which is 2.71 minus rho bulk if rho bulk is less then the numerator becomes bigger when the numerator becomes bigger my density frosty will become even bigger okay so the density porosity here in front of the sand will be much bigger so let's look at this it will be higher than 22.6 so this means my density frost would be much higher look at this the separation is still there but it becomes big so the notice that you will see if you are in a gas reservoir that the sea separation still exists in in in the sandstone but the separation becomes very big okay so the separation was that small limited area which is around 6pu in the normal oil but it becomes much bigger in case if you have gas so if you have gas and sandstone reservoir you will see the separation between the neutron density are really big okay also you will see here if we calculate the porosity of the limestone full of gas then the density process will be much higher than 20. so in this case you will see also higher than 24 the lime higher than 20 means the new the limestone scale the limestone is not going to be overlaying anymore even the limestone will actually have separation but that separation is due to gas so the separation is due to gas becomes bigger okay if i go for the dolomite and i do the same the process will be higher than 12.5 so that will be this new one higher than 12.5 so you can see here the separation becomes bigger okay so that's that's that's the way that you will see the gas effect any separation you will see there becomes becomes bigger except for the separation of the dolomian becomes smaller so the separation in case of gas in the dolomite okay becomes a little bit smaller why because actually it increases the porosity so you can see the density process increasing going to the increased number of 20 so it isn't closer and also the neutron will be will be decreasing as well so as you can see here the gas effect will make the separation even more even the the the two that you were overlaying which is the limestone of a limestone scale they used to overlay no now they will also separate so the effect of gas or if you are dealing with gas bearing reservoir expect the neutron and the density will separate you'll see huge separation if your reservoir is sandstone you will see a small separation if your reservoir is a limestone you will see even a smaller separation if your reservoir is doloming okay but you will see separation anyway you are not expecting that the neutron and the density will separate in front of the limestone because we said limestone on limestone scale they should not separate that's true if you have oil but if you don't have oil if you have gas the gas effect will make a separation even in the limestone okay how about the the neutron density about the porosity the process is still the average porosity remember we said the neutron process is not the correct process the density process is not the correct process the correct process is the average neutron density process the average neutron density process even in the gas reservoir is the correct process so even if you see the more effect of the gas reservoir you still have the the average is the correct the correct process okay so identification of gas reservoirs that gas zones are easily identified using combined neutron density logs very easy density neutron neutron and density logs are separated more in gas reservoir compared to oil and the neutron density average process is still your right rusty even if the gas takes distance okay i need to summarize this because it's very important here is the situation where you have oil here here is the type of separation very small separation in the limestone in the limestone for oil they are overlaying and the dolomites are also separated okay if i look at the gas reservoirs now what will happen here that this one will increase okay and you can see there this one would also show separation and this one will also show separation so the gas will do separation but it will increase separation for sand increase separation for line and decrease separation for dolomite okay so this is actually the major effects of gas reservoir so to identify say this is a gas zone look at the separation separation will be huge in the sandstone and it will be separation on limestone you don't expect any separation between neutron density on limestone unless you have gas reservoirs so if you have a gas reservoir you see the type of separation also you see the separation dolomite but you may see you may see the separation in dolomite shrinking a little bit the reason that shrinks because the effect of gas on the on the dolomite okay right again the the the right porosity is the average nutrient reciprocity as we defined it before right now how can i identify salt and anhydride from those again guys you always learn this you need to actually to go to the basics of things to really help you identify things don't don't memorize what the tool will do or what the tool will have all the two rules show so and i just go and see what are the basics of the tool measurement let's just go and for example so salt is highlight salt is actually we call it halite so how the highlight will react on the neutron and the density let's just go for this over and look what is halide light is nacl sodium chloride ask yourself a question now is there any hydrogen in here the question is no it doesn't have any hydrogen so if it doesn't have any any hydrogen what the neutral tool will do neutron tool is not going to find any hydrogen if it didn't find any hydrogen it will give you zero porosity it's as simple as such so you don't don't try to memorize things understand what are the basics of all these tools the basic is our light is nacl the neutron tour when it sees halite it doesn't see any hydrogen since the neutron tool is not seeing any hydrogen it's not going to give you any porosity as simple as such so in front of a light it will give you zero thrust okay so this is the third thing so first of all not radioactive so the gamma is not going to reach any high gamma ray this is one thing second second it doesn't have any hydrogen so in this case the neutron will give you zero how about the density density of our life is 2.13 so i will see also low density so i will see zero porosity on the neutron i will see low density under under density i will see low gamma ray okay so in this case however there is activity and if the recipe will read low or high okay first of all salt is sea salt actually dissolved in water no it's actually a salt bed salt bed is very resistive somebody say oh salt is actually conductive no salt water is conducted but salt itself is not the salt bed itself there is no water in there salt water is the conductive worm not the soul salt is not conduct salt is very resistive you cannot actually pass any current through salt bit okay but if you put the salt in water it makes water more conductive so the soul to water is the conductive then some people actually have this this mysterious thing in the in their minds no salt is not conductive soul to water is conduct okay so that salt is very very resistant salt will be very very resistable but there has no water in there so salt is nice it's not it's not an acl solution salt water it's salt red salt event is very very resistant let's just take an example here here is a look for example if i look at the gamma ray it is very low gamma ray as you can see there okay and my density here is reading low this is the one point nine five it's eating very low my neutron is reading zero here is the zero so my neutron is reading zero my density is reading low my gamma ray is leaving low my resistivity is reading high okay so these are the cases now my neutron is reading zero my density is reading low my gamma ray is reading low my resistivity is really high that's a typical typical response of any sort so here is my neutrons reading zero here is my density is reading law it is minus 50 is reading high it is my gamma rays reading the four components we just talked about these four signatures if you see the four signature signatures at the same time all combined in one of the sections of your log you need to mark this section as soul section low gamma ray low density zero neutron high resistivity that's a soul a light section okay so the highlight is very easy to find out by just knowing the properties of whatever you look at and how your tools are measuring what are these two measuring so in this case you can easily easily find this out you don't have to memorize or keep in mind or whatever no it's just knowing the responses of your tools will help you out okay for the anhydride on neutron density is the advantage to go back and see what is anhydride anhydride is calcium sulfate caso4 calcium sulfate does it have any potassium thorium or uranium no so it does not have gamma ray it doesn't have any hydrogen no it does not have hydrogen if it doesn't have hydrogen it will read zero neutron it's very simple neutron reflects hydrogen so if it doesn't have hydrogen it see it gives you zero zero prostate also it doesn't have any uh potassium thorium or uranium to give you gamma ray okay however the density density is very high so the difference here so anhydride will have very low gamma ray and hydride will have zero process similar to what similar to highlights but the halide density is very low the 2.3 the density here for anhydride is very high so the difference between highlight and anhydride is mainly in the density the other three are the same you will see low gamma ray you will see zero porosity and also you see very high resistivity because there is not really any water here in the caso4 to make the resistivity reading low yeah there is nothing there but calcium sulfate so in this case however the resistivity so also no water it will give you a very high resistance if i go to the same law yeah and that's that's in the gulf of sewage in egypt we go to the same log the second section look at this section porosity is very low okay similar to the porosity of the soul okay so it's very very low processing well look at the density it's very high look at the density here very low density look at here very high density so the density is very high the neutron is reading zero the resistivity is reading very high the gamma ray is reading low so it has low gamma ray it has zero porosity it has high resistivity the only difference from this and the light is the density here is reading low and the density here is reading high so once you look at this this is your low gamma ray similar to this but instead of low density will be high density zero neutron zero neutron higher safety high resistance so what is the difference between halide beds and anhydride beds the main difference is the density density and highlight will read low because the density of highlights density and anhydride will read high because the density of an hydra tool well is very high so this is an anhydride bed and this is the highlight so it's very straightforward by just understanding what are the tools measured and what is the property of the thing that you're looking at look at the property and use the basic understanding of your laws where every log looks the thing the neutral log looks at heightening density looks at density resistivity looks at is it conductive and the conductivity happens with having by either either any metallic components or any hydrogen okay so in this case the the conductivity of the water components and the metallic compounds you don't see this in any one of these two neither the light nor the anhydride that's why the state has to repair if you look at the rock itself does it have potassium thorium and uranium no it doesn't so in this case white should read the high gamma ray there is no reason for it to be the high gamma ray that's why they read so identification of anything guys just just look at what are you looking for what are you looking at and then decide what are the components of all these minerals and what every tool will react with every tool will react to something something specific in the composition of your of your okay so this is actually the first two things which is identification of the or at least the evaluation of the gas bearing reservoirs how the neutron density will react to this and we talked about the separation then the the identification of sole beds and anhydride beds as well now many of you actually talked about the variogram processing okay very grand processing let me let me remind you at least warn you a little bit because it's a very tedious process uh i will go through it and try to make it easy on you guys how to how to do it because billy graham as i said is not as easy as a histogram but let me start what what is a perigram verigram is mainly trying to do some statistical evaluation of data based on the spacing between wells when we when we talked about the histograming before histogram does not take into consideration the word spacing histograming i can do for a single well okay or i can look at the variation across so well but without including the very the the spacing between one and that's puts a drawback on using the histogram for characterization of multi wealth we need to find a way to look at how these wells are characterized together as a function of how far from each other they are okay so the variogram will give you this so the very gram provides quantifications of the variations based on distances between words okay all right so for example let's just take a reservoir here is a reservoir all right and for for the first one here is it is our area my area would be divided by x axis and y axis defined by x axis and y x each one will has a next location and y location okay and also there is the z axis where this is the depth so everyone will have a location on the x y plane and also we'll have measurements on the z which is this axis and let's assume that here is the layer that you will actually interested in here is your reservoir and your reservoir i'm interested in for example the variation of porosity across my feet i need to look at variation of porosity across my feet so here is my reservoir is my target and i need to look how the porosity is varying across my field based on the distances between the wells okay so this is first of all let's assume this here is my first one here is well number one when our number all penetrated the reservoir and here is my reservoir section and here is my x y point whole as is drilled in x one y one so i actually decided the location of my well on the x y plane so i have x one and y one for the location and also i actually try to calculate the average porosity using histogram for a single well so from the single world i can put a histogram here and i calculate my average process i call it fee one four well number one okay so i will use the histogram in every single well and i get the average porosity using the histogram for this well that doesn't i don't need to go for x1 and y1 there's no it is only in the z direction so in the z direction i will calculate my average process using the histogram okay so i did this for the first one then we decided to drill a second one second wheel would be in a certain location x2 and y2 so the second wheel is in a different location penetrated my reservoir and also i measured the porosity in the section that the second will actually intersect it in my reservoir and it give me an average of p2 so the average porosity in the first world is v1 average porosity in the second oil is fitted remember these two wells has a certain spacing so there is a spacing between the two words i can actually calculate the spacing if i have x1 and y1 and i have x2 and y2 then i can find the spacing between these two r which is the square root of x1 minus x2 squared plus y1 minus y2 square so this is actually the distance d12 means the distance between well one and well two so d12 is the distance between the first well will1 and will two and i can calculate the distance between any two wells d i j whatever will i and will j is actually x 1 here minus x 2 square plus 1 y 1 minus y 2 squared or to make it a generic x i minus x j squared plus y i minus y j square so i can actually get the distance so now i have the distance between the two wells and i have the average of my porosity for every well by itself using the histograming for the first well and the histograming for the second one now let's assume i drilled the third one the third one now will have a location x3 and y3 now it also penetrated my reservoir and i will be able to calculate my with the histograming my average porosity pc of the third one so now i have three three words what are the combination of distances in this case first of all i get the distance between x one y one and x two y two already have this two and then i have to go x one y one with the x three so the distance between x x1 or will 1 and width 3 and the distance between will 2 and world 3. so now i will have 3 distances all right so the second distance is the distance between 1 and 3 d 1 3 i will go i use this equation d i j to calculate the distance d 1 3 be the square root of x 1 minus x 3 squared plus y 1 minus y sub square so i got the distance between the these two words again there is another distance between well two and well three i will call it d two three d two three is the distance between two and three which is simply x two minus x three squared plus y y2 minus y3 squared and i take the square root so i can actually decide the distance is between all wells okay and also i use the histogram to get the average frosty for will three average prostitute will one average average processor well so now i will build a certain table that table goes into what is the distances between each well and which two wells and also what is the average porosity for each one okay so i'm collecting data now all right then i will say okay there is something we will define called the variance variance or gamma what is the gamma well v1 is different by v2 for example the average porosity here is 20 pu but the average velocity here is 18. right the average the average porosity here is 17. so what you do is once you calculated d12 which is the distance between one and two you actually get the difference between plus p1 and plus t2 so you say p1 minus p2 here is the difference all right and you make it square because you don't wanna if you wanna and p2 or v2 y minus e1 it doesn't matter if you make it square you will actually take care of the negative sign so it will be v1 minus v2 square so i got the distance d12 and the variance of the porosity between p1 and p2 then i calculate the distance d13 and i get the variance between one and three v1 minus p3 squared then i get the distance between two and three which is d two three and the variance between p2 and p3 which is p2 minus v3 squared you add all these variances you divide them by the number of wells and you take the square root we call this a variance so it is actually the variance gamma which is a function you get the differences how this the well is different from that well you go for v2 minus v1 squared p2 minus v3 squared p1 minus e3 squared and i add them up then i take the square root of all and divide them by the number of words so you add up the variances you sum them up you divide them by the number of words and you take the square root we call this variance okay right that's a very simple eq a pretty simple example actually in reality in reality what we usually do is that is here is how we do p1 and p2 we get the difference squared p1 and v3 with the different square p2 and ph3 you get the different square you sum all the differences you take you divide them by the number of wells and you take the square root it gives you the gap it gets more complicated now if you go to reality reality is okay once you finish this you go for the distances versus the variance so now we have distances d one two d one two one three due to three and so on you get that diff the distance is versus the variance so you calculated the first distance for just variance second distance versus the variance and so on you plot them distance versus variance and you get the relationship now as you can see these three wells okay as an example we are in correlation you can see is actually increasing our this well it's actually it's off correlation so we call this distance is a correlation it exists between this well and this one is off correlation so i can look at statistically where is the distance of correlation different than the other part of the reservoir and where are the reservoirs are correlated as a function of distance to variance or variation that's why we put it very eugene the variance as a function of distance okay let's just do this in in in real example here's here is a lead example i have actually multiple wells here how many ways they have about 16 wells so the number of words actually i have 16 ones so the first step is to list all will's location and the property of interest okay for example i have 1 1 2 3 up to 16. everyone has an x and y so this is the x for well one and y for well one x for well two and y for w and i'm interested in porosity so this is the porosity of one two three and so on up to twelve so i make a list of all the data i have well one x and y and porosity it can do you can do that for frosty clay volume water saturation permeability whatever you like you can do very grand for any any uh property that you wanna do for so the weld x location why location and the property right so this is the first thing you need to do is to list down all of these ones okay then you create a table of all possible will distances it means the will distance is x i minus x j squared plus y i minus y j squared that's doesn't take the square root these are the distances no repetition it means the distance between one and two is a different is the same as the distance between two and one so you don't go and calculate the distance between well and two one and two then you calculate it again as two and one it doesn't make any sense because the distance between one and two is the same as two and one okay so it's either use one and two or you use two and one okay so that's why we call it no repetition you don't repeat it okay second meaning the distance i j is that this is the same distance j i okay mathematically how many combinations you will have okay it's actually mathematically it's n plus n times n minus 1 divided by what is n n is the number of words as i told you guys from the beginning it's a very tedious process so because it's a lot of combinations that you need to look at n is the number of words so number of words is 16 then 16 times n minus 1 which is 15 16 minus 1 divided by 2 it gives you the total multiple or total number of combinations that you may have between all the 16 words or any number of words so in this case the number of words is 16. so how many combinations between distances i have in this 16 wealth sure look at this only 16 ones we have sometimes we have we have 300 400 worlds look at how many combinations that you will have thousands okay so it's a number of of worlds here is 16. how many combination of distances i will get between the 16 wells first of all it's actually 16 plus 16 times 15 n times n minus 1 divided by 2 you have 136 combination of distances and variances okay everybody understand that so in this case you will have a lot of correlation that you need to build tables for and you see the variability of it as you can see is much harder than what the histogram is all about okay so you look at the the combination of distances and the and the variance between all these distances actually the way we do it is to build the table a table has x which is 1 2 3 4 up to 16 and you can do that on excel and also the y 1 2 up to 16. okay here is the wells that well by itself one and one one and one the distance is zero so means there is no these are the worlds by itself then i have well one with will two we call it d one two well one was will three so d three one d three two where number four was one before one with number four was two or four two i don't fill the other part because it'll gonna be four three two is the same as four two three so it doesn't it doesn't doesn't make any sense to fill the upper part we only fill all the possible combinations between wells so this for example here will six when six will have at a distance between six and one distance between six and two distance between six and three six and four six and five and you go to well seven seven one seven two seven three seven four seven five seven six and so on okay then you fill this if you did you do this in excel it would be an easy thing but you know this is how we fill it if i do it on excel here are all boss possible distances based on the will locations i have as you can see huge type of calculations that you need to decide the 136 spacing between the 16 wells so the 16 worlds created 136 spacing okay all right all right once you did this then you have to do what you have to list all possible combinations in tables for example i can see here well one and one will one and the the orders will won none will two will one and one two i will three and well one or four and one and so on until you go for well 16 and well one then you have to well well one two two and well one and well two and will 2 and so on to have all these possible distances between wells for example here is the possible distances for will one it is a possible distance for a distance from well to and so on possible distances for world three so you take it away by one so well one will have a distance between one and two one and three one and four one and five and you list the distances then will two would be two and three two and four two and five and you list all the distances uh uh will three here three and three and two three and three three and four three and five and so on okay so you will have all this possible combination of distances between worlds okay so you list them all okay then arrange them arrange the distances from low to high for example here are the distances of zero means the will on itself and distances will increase here this is 200 this is 205 281 300 370. you can do that easy again on excel because excel can arrange things ascending or descending okay so you arrange all the distances from the zero all the way to the maximum distance that you have once you do this there is a zero distances there is distance is increasing this way okay so here is zero distance means the will on itself so the will will will have its own variances with itself okay then you once you do this which you have now you decided what is the distances between wells then you go do whatever you used to do for the histogram which is the range of the data what is the range of the data the minimum value of distance and the maximum value of this minimum value of distance would be zero here is the minimum value and here is the maximum value so we have the minimum value and the maximum time we call this range so the range will be the maximum value we found from the data data is 2100 minus the minimum value zero so the range is 21. now we divide the range into bins remember that we throw them from the histogram we divide the range now what is the range range is the distances between words that's how now we combine the distances with the histogram so the the histogram now will take care of the distances and we see the variances between between the different ones so here is the number of events that say thin bins okay and you decide on the range how can i get the range you divide the the the range on the number of bins that you decided then each bin would be 233 distances or 233 meter or whatever the distance that you measure okay then you list all these ranges in bins like with exactly what we do in in the histogram so look at here it has been number one bin number two up to bin number ten because you decided that the number of bins are ten here are the distances of the bins and here are the the remember when we take actually the range we decide on what is each each one of these bins will be it has been number one bin number two bin number three and so on so actually as we used to do for for the histograming and also we decide for the midpoint of each one of them all right so we have actually defined the pin and the middle of each bin right once you do that i know it's as i told you it's it's a very tedious process but it's simply it's simply because you can see a lot of calculations here and i'm just taking a very simple example a well a field that has 16 worlds now if you have 300 wells imagine how many calculations you would do software's actually do that for you but that's how the software's work so in case the software does not give you the proper distribution and you feel something is wrong so you know exactly what went wrong with the software and you go back and you look at your data one more time so let's just continue on this you actually decided on the bins and here you have the each bin minimum and maximum and you and also the middle of each bit okay once you decided on the start and the end of each bin you look at the number of wells in each band your number of words here is 16 in the bin number one number of words here is 7 25 26 23 18 and so on you have seven wells that that actually lies between these two ranges to the distance 116 to 350 i have seven worlds that has this distances i have 25 worlds that has distances from 350 to 580 and i have 26 worlds from 580 to 816 and so on so i haven't decided number of words that goes within this range of distances once you do this then you calculate the variance now variance is vi minus vj square remember plus t here rusty from l1 minus plus c with 2 squared and you add them up and you divide them on the number of wells then you take the square rule to get to get the variance once you've got the porosity and and the distances you calculate the variance for every single group of data is the variance in zero zero between themselves and and if you go to the second group you calculate the variance here between between v1 minus v2 uh few if you if u3 minus v4 5 minus 6 6 minus 7 and so on you sum them up squaring you sum them up and you divide them by the number of wells you get the variance if you do this for example it is 12.7 minus 15.8 squared 7.6 minus 15.2 squared 11 multiply 9 minus 7.6 squared and you sum them all up and then you take the square root of sum divided by the number of words which is seven seven wells in this case yeah so you get the variable you repeat this for all of them okay here is another example of other group of data where you calculate also the variance as 14.05 okay then you list finish all bins and then you list them here is the distance versus versus the variance then you start plotting distance versus variance here is your distance and here is your variance and you can see all these are in correlation and these are off correlations okay so wells and correlation words are of correlation as we saw in the the previous example and then you say this is what's of correlation these our world's in in correlation okay so only words with those distances this isn't 1400 feet our world's in correlation so now you can see the words the task relation together has to be within certain distances and the other exceeding these distances would be of correlation but you cannot actually find this from any any type of histogram okay as as i said this is a tedious process but the whole idea is if you look at that they would try to compile all possible distances between wells and the variation between the parameters between wells and you start building the correlation between distance and the variance of of the parameters and that's what you call the perigram as a function as a function of distance okay right actually i'm done with these three uh components that we started uh saying that we will cover this and i'm now ready for any other questions that or any comments even what we cover so what if anybody has anything that's not clear or i have any different questions that they can answer in the upcoming few minutes right uh i think thank you dr mustafa yes uh thank you dr mustafa as usual the session was very important informative and clear we got some other questions i will pick some of them to answer someone is asking i don't understand what are the difference between plastics and carbonates for example i see limestone in both in both of them so can you explain okay actually when i say when you say clastics and carbonates okay that's at the positional empire plastics is mainly uh in sandystone which is silicon dioxide sio2 okay so silicon dioxide represents plastics plastics can can vary in grain sizes for example you can say coarse grains and fine grains when when the classic becomes fine grains we call it silk stone so we have sandstone and we have silt stone sometimes as you said you can find limestone within plastics but that's not actually takes the classic to be carbonates no we call this calculus sand okay so we have actually definitions for this there is nothing sharp in nature okay so you can actually find a limestone in in classics for sure but we don't say this is a limestone formation called this calculus scent it means sand that has some calcite in it calcite is carbonate okay you can also find some dolomite in sand yes you can you can find some sand in carbonates yes you can okay but when you say that the majority for example if i have eighty percent of my rock is sand and twenty percent is calcite we don't call this carbonite because it's dominant by classics okay plastics is a sandstone it's a silicon dioxide texture it's green okay but if i have eighty percent limestone and twenty percent sand we don't call this sandstone we call this limestone because it's the majority of it so the existence of some other lithology included in certain majority of lithology that doesn't change the name okay so it's to to be more careful if you really work professionally you say this is calculus okay or we could call this dolomatic limestone dolomatic limestone it means it's a limestone that has dolomites in it so there is nothing called clear limestone for example in my in some in some in some reservoir there are clear limestone but some other limestone you can see dolomite built in the limestone so you have variation and there are so many process processes actually or processes to do this so you're right what's when you when you start naming a name aim it to the majority if you have eighty percent sand then it's a sandisk and has twenty percent calcite yes we call it okay if you have limestone that has dolomatic dolomitic line okay so do we have this type of naming but you name it on the majority of the lithology that you have okay yes ma'am uh okay uh what are the required parameters to build a basic reservoir characterization model and how okay that's a very long question uh well first of all let's forget about the parameters first i think you need to get yourself strong in how you look at logs first okay and you need to get yourself strong if you are not very strong in geology get in a very good contact with geologists okay you cannot do characterization without having an a full understanding of the environmental deposition how this reservoir is built okay the the environment of it okay uh being in uh i don't wanna go into details in geology because i don't wanna complicate things here but at least you need to do the environmental deposition okay uh what type of reservoir you're dealing with you need to go into depth with the composition of your rock understand with the geologists what is the composition of your rod you need to understand the response of your logs because actually the input that comes from the geologist will be in a limited time now the majority of data that you would use for the characterization is logging because we do logging in every single well okay you don't do coding in every single one but we do logging in every single one so you will learn the geology and the deposition and the and the properties of your rock from one two or three core dwells but the majority of your work is to look at loss so you need to understand the logging response very clearly you're not memorizing it you really understand it understand it very well the response of your law second thing is you need to tie in between your understanding of logs your interpretation of logs and what the core is telling you that we call integration between core and log that is that's the need to be done before you even even start talking about characterization so the geological input the depositional input the logging understanding the integration between logging and coring these are very important factors that you need to start really teaching yourself or training yourself on how to make this and you have to get yourself very strong in this after that you need to look at all the wells need to build your understanding of how to look at multi-wealth data okay how to do multi-wells processing because you cannot actually process every wheel separate and when you when you choose parameters for your reservoir you don't choose it on a single wall by single well you can do that you have to have to learn how to choose multi-wells parameters okay when you look at the statistical variation you don't do this in a single world for a statistical variation you have to look at multi wealth if you go for any softwares for characterization you see two options multiple single wheel options and multi-wheel options okay so you have to teach yourself restore the skills to do full analysis for a single world then the skills of combining wells together there are so many steps and believe it or not you will gain this through the years uh nobody will teach you this or the steps you will learn one step at a time and then you would see yourself later on that you started to grasp everything and you see how all these pieces of the puzzle are connected together to be a good uh characterization engineer okay okay uh next question is uh what is the difference between core helium porosity and porosity flow and core fluid porosity no okay well uh there are two ways actually of uh of measuring porosity in the lab okay one of them is to heat the core and to collect the fluids that come out of the hole okay for example i have a have a sample of a core here and now to get the fluids out of it i will not do this by pressure it's not going to work okay so what we do we heat this this this piece of rock and we extract the fluid that comes out of the eaton because it will evaporate and from the evaporation we can collect them after that by condensing to evaporate and condense to get the flu that's how we extract fluids we call it the fluid thrust this is not really a good prostate measurement it always underestimates porosity because when the plug actually comes to the surface the plug was at the bottom at 10 000 feet 15 000 feet under pressure once you actually take it to the surface if you are not preserving it properly the fluids will leak out okay so you will lose some of the flows so normally you see that the liquid porosity is less than reality but once you actually cleaned it and now there is nothing inside it now we can use the helium helium will be measuring your frost and the helium has a very important advantage it's not a liquid helium is a gas so helium will will actually go and inside any type of pore even the small ones okay so helium will go through the small ones and and it will give you exactly the total porosity or it's let's call it effective process in this case so it will give you the porosity because if the gas will fill the whole the whole rock even the small force if you try to do this by fluid injections you're not going to succeed so the fluid processing or the liquid the liquid frosting is the porosity that we measure by extracting the fluids from the core and this is normally normally less than the helium process okay helium process after you clean the the the plug you actually use the helium as the measuring uh measuring gas for uh for your frost okay normally helium porosity is higher than the liquid porosity and the helium process is the most appropriate one in this case next question do i histogramming all the gross zone data or only the net pay section uh you only do that any if at anything actually uh when you even do calculating effective processing i saw some students that happens also and where i teach some of the students when they pick up for example the gamma maximum and gamma minimum for clay they go from top to bottom for the well that's not right okay you need to concentrate on your zone of interest okay and also just just give yourself plus or minus whatever 100 feet or so above if you're if your top of the reservoir is let's say 10 000. give yourself a hundred feet above it and 100 feet below it so you put your reservoir on in this sandwich and try to pick the parameters of your reservoir because if you don't do that you will add some junk data to your reservoir that doesn't belong to your reservoir okay make sure that you do this you do this around your reservoir and work with your geologists to make sure that you're not adding junk to the zone that you are doing you're doing the calculations on so yeah you need to be very careful when you do that and now this is the last question uh someone is asking so the negative uh separation isn't the best way to determine gas bearing reservoir am i right what what do you mean by negative separation it's not gonna negative separation the more separation you have okay that the the neutron density will separate more i'm not saying negative okay for example let me give you if you want to if we want to do this i don't want to say numbers because some people actually stick to these numbers which they may differ from you know one place to another but let me give you at least a rule of thumb if the the if you are in a sandstone formation and you are in an oil reservoir expect your separation between you and this you will be between a maximum of six cpu six first units difference between neutron nets if you see more than this okay try to think of do i have a reservoir under bubble point so if i see so for example seven or eight that may indicate that your reservoir is under bubble point and gases started to build up if i see 10 12 15 pu differences you are in a gas bearing so the separation measured in porosity so look at the the reading of the neutrino and the density and and try to subtract these two readings if they are six pu or less you are in an oil reservoir if it's above six pu say seven eight you are in a reservoir under above the point if you are talking about 10 12 15 15 then you are in a gas level okay and that's it we would like to express our deepest gratitude to you dr mustafa for the course it was very informative and interesting and as usual please be informed that the lecture will be uploaded to pi petrol youtube channel and i would like to inform you all that there will be three timings for the final exam 2 pm and 8 p.m on friday and 2 a.m on saturday all in egypt time so please choose one of the mentioned timings to solve your exam thank you all and stay safe