Transcript for:
Bond Log Basics and Interpretation

so good morning good afternoon and good evening hope you are all doing well and staying safe it's my privilege and pleasure on the behalf of people petro sp egypt to welcome you here today my name is mariam shreve and i am senior i am a senior petroleum engineering student at the lebanese american university and i'll be moderating today's session our webinar today is about bond log basics and interpretation which will be presented by an outstanding speaker with an extensive experience in cementing cementing and bond log interpretation so without further ado our speaker for today is engineer kirk harris engineer harris holds a bachelor degree in civil engineering from purdue university he began his career at halliburton where he worked as a cementer operations and research engineer and finally technology as a technology manager afterwards engineer harris became the global cementing advisor for occidental petroleum talisman energy and repsol currently he is the technical advisor for thorough thorough bond llc which provides technical support for cementing and bond log interpretation finally engineer harris has been the cementing advisor for the following regions asia pacific north sea europe africa and premium basin and the gulf of mexico so please help me welcome engineer harris we are delighted to have you here with us today and as a reminder if you have any question will it related to the technical content of the presentation please feel free to drop it down in the q and a section and we will try to address as much questions as possible now hope that you will enjoy this session today and engineer harris the mic is yours okay thank you very much thank you for the introduction it is a privilege to be online with you today we're going to talk about monologue basics and interpretation i recognized in the participants i recognized a couple of names i recognize laura bell and mustafa and so i want to say hello to you i don't know if anyone else is a participant that has joined one of our webinars before our independent webinars but it is great to be here and on behalf of the arab oil and gas academy uh let's begin the agenda we're going to talk about the basics both for the cbl and the ultrasonic there are tens of tools we could cover for bond log interpretation these are the main two and so we'll look at the basics and then we'll talk not only how the tool works but the most important thing and that is how do you read and interpret these things and we have a process we call it the five c's and i welcome you now to go for the sixth c which is a good cup of coffee the great thing about the bond log is it's an enjoyable process to sit back and relax and read the bond log and the last thing we'll do i'll invite you to practice a bond log interpretation with me now the problem is i wish you were gathered around the desk and we could lay the logs out and we could talk about this and i could hear from you sometimes when i do a webinar i'm just talking to a screen but i'm still going to ask you questions and i hope you will engage with me and answer some of those questions and we're going to begin by just looking at a log and i'm going to ask you why are you here i noticed someone asked if a certificate was going to be given and that is a good thing to have but what you're about to learn i promise you if you're in the oil and gas industry you're going to run into these almost every position in the upstream oil and gas industry will eventually find themselves gathered around looking at a bond log from drilling all the way to final production and abandonment of a well so what you're about to see i promise you if you learn it if you practice it you will use it now how we read one of these things we'll take a look in a bit the reason i know you're going to is because i've i've run into so many people in my career i not only do so many and i look at bond logs almost every day and what you're going to find yourself in a position someday you're going to find yourself gathered around a table like these people this happens to be my favorite television show i know none of you have seen this television show but it's a pretty good show but only uh i've only met a few people that have seen it now i have the entire dvd series i can ship to you if you want to watch this show it's about a family that lives in the country in the united states and they lived during the depression and they didn't have a bond log what i'm about to show you was invented in 1959 we ran our first bond logs in 59 1960 and we still use very similar technology but here are the people that are gathered around this table and these are the kind of people that will gather around the bond log during your career so i'm going to ask you very quickly and i know you're not supposed to do this but i'm going to ask you to judge a few of these people i know we're not supposed to judge people especially by their appearance but i'm going to ask you to do that these are people they didn't have a bond log they have a radio instead but these are the people that will be gathered around the bond log and you're going to walk into that room and you're going to get engaged in some way with the monologue and that's what we'll study today so let me ask you just a few uh which person on here has the most experience which number and i know you're not saying number eleven if i pull the chat feature down which i would love to do because i see some of you answering the question i don't want to block a future video of this but i hope you've said number nine or number eight the least experienced of course is number ten who hates the bond log who wishes we didn't have the bond log the bond log costs money it costs time you will hear about the bond log you can't trust it it's hard to read we're going to simplify the reading of a bond log who hates the bond log in this picture who's the one who doesn't like the bond log i hope you've chosen number eight this is the grandmother in this particular show and she hates everything she would surely hate the bond log i'll ask you just a couple more who is the most unintelligent person in this picture who knows nothing about what's going on because you're going to get experienced people in that room you're going to get people who don't like the bond login are very cynical about trusting the bond log you're going to get people that don't know anything although most of the young engineers and you see some of them gathered around here are smart and have energy i don't know who you've chosen but i think number six has not a clue what's going on and finally who is the smartest person in the room this is a little tougher take a look at them who's the smartest some of you may have chosen one or two but they're managers and they they may be smart but they don't know the bond log it's number five look at him he's focused i think he's looking at a bond log and he's going to give us the right answer we're going to look at this family one more time before we interpret and the other thing i will tell you is when you walk into a room to interpret the bond log if you have experienced people angry people managers young people they're going to be noisy there is a lot of talking when you walk into the room someone has already interpreted the bond log and it's your job to know the bond log well enough to be able to quiet the room and get the right interpretation now this is the actual people gathered around the bond log this is actually a log that we're looking at in columbia in south america and so they're actually smiling because i'm taking their picture but they were focused on interpreting this particular bond log we're talking about sound waves and when we talk about sound waves what we're going to look at i want to bring up a couple terms you're going to hear several terms about the bond log but i want you to think of ring like a bell would ring and i want you to think of resonance i want you to think of ring and resonance and we're going to be looking at bond logs and we're going to be listening for ring and we're going to be listening for resonance i'll give you one example and this is the basics of the bond log here's a crystal glass it's uncemented there's no cement and the bond log is going to tell us if we have cement or not and so we're listening for sound waves and if you hear sounds like this that's ring if i put cement around the casing or around the glass no more ring something you may not be able to hear [Music] is that after the ring i continue to hear sound you may not be able to hear through the mic it's an echo it's a ringing it's what we call resonance here's another way to explain it this is an airplane it happens to be egypt air for uh this is honoring ahmed but i live next to an airport in lafayette i don't think egypt air flies into lafayette louisiana but when an airplane does fly in i know an airplane is flying by our house is located very close to the airport and i can hear the sound of the airplane that sound i call ring it is a loud sound i hear with my ear but i hear something else i hear something else i hear the ring but i look over and i see my glass rattling i see a vibration and that is the resonance so the sound waves that we are going to be looking at i want you to think about ring what we have in the middle here is a bond log the cbl it's based heavily on ring the ultrasonic we'll see is we're looking at resonance and we'll see that a little more clearly as we look at the bond log let's do a quick five-minute review on what we're even looking at it's the cement job and here are the basics of cementing before we get into evaluating that cement job when we drill a well we pull the drill bit out of the hole we run the casing we will then circulate the hole to get it clean so that the cement can fill the hole we pump a spacer down the casing we drop a bottom plug that wipes the casing and behind that it also is separating the spacer from the cement we pump the cement we're going down the casing and up the annular space we're mixing and pumping with a high pressure cementing unit we're pumping through a cementing head we'll look at that and we're pumping it down the casing up the annulus behind this cement we drop a top plug that top plug we will displace down the hole with a mud or a water when that plug hits the top of a check valve a collar there which we call float equipment the job is over the plug can no longer travel and the fluids cannot travel we then open up the casing to make sure the check valve is holding and the cement doesn't come back up the casing we then wait for the cement to set up and we run a bond log in many cases after the cement has set so we mix the cement here we are mixing some cement this happens to be out in west texas we're pumping the cement through a cementing head through a manifold of valves through high pressure iron at the rig floor we drop the bottom plug b we pump the cement on top of the bottom plug and then we drop the top plug and we cement the well we then displace that with fluid we measure that fluid this is water being measured at the unit by halliburton and we'll displace that cement down the well we circulate down the well up the annulus and there we are taking cement returns back to in this case it's actually going into the seller that particular job was in the country of oman and then what do we do cement is placed i mentioned it before what do we do next what do we do after we place the cement we wait and we wait for that cement to set up to get hard to bond so that we can run a bond log usually we will wait anywhere from 24 to 72 hours before we run a bond log so that we have good cement that we are testing and checking out at the end of the cementing operation we hope it looks something like this it would be great if we could go in and we could cut the well up and take a look at it but we can't but we hope we get something like this casing filled with cement between the formation and the steel casing and we're going to run a logging tool right in the center of this casing and we're going to send different kinds of sound waves out and we're going to see what is behind that casing and in between the casing and formation so here we are it's funny because if you wanted to go take pictures of things uh it would be nice if we could see a wellbore or we don't we get straight lines crooked lines different colors different maps and just looking at this you're going to be confused if you've never seen one before what am i looking at and so we're going to break it down the bond log and the ultrasonic log so the cbl basics here is the bond log tool the bond log tool is sending out a sound it's actually a sound if you have good ears you can hear the sound it's at a frequency of 20 kilohertz but this tool when you activate it sounds like this a very fast click and it's being sent from a transmitter activated it's a crystal that is activated by an electric wire line by electricity and it sends out from electricity it sends out mechanical energy sound it receives that sound it listens for that sound three feet away it also listens for that sound at a receiver five feet away and when it receives that compressional wave that creates electricity and the electricity is sent up to the logging truck and we measure these sound waves in electrical energy in millivolts so we run the tool now in the middle of the well and we want to find out what's on the outside of this steel casing i'm showing one sound wave here going from the transmitter down the casing to the three and five foot receiver but actually the sound is going in all directions in a sphere of sound and this path just happens to be the fastest path because it's traveling through steel and sound will travel through steel faster than other materials so the first thing we hear at the three and five foot receiver we're listening for that ring the first thing we hear is sound traveling down the casing and if that sound is strong we know there's no cement if that sound is weak we know there is cement the problem is is when the sound is kind of weak but kind of strong then you have to learn to really interpret but we're listening for sounds with the bond log tool if we have cement those sounds will travel through the casing out into the formation now the sound traveling down the casing is weak why is it weak all of the sound went out it didn't go down the casing because we were connected by a solid it's based on something called snell's law and when two solids are together sound goes through them when there is a solid and a liquid the sound is reflected and stays in that casing so here's the sound wave traveling the first sound we hear and up in the logging truck we're looking at these waves on the oscilloscope we're looking at electrical energy waves and the first thing we see is the sound coming through the casing and we're going up the well so we're getting sound waves continuously at every depth so at one depth we get this sound wave and the first part of the wave we look at it is sound coming through the casing the second has gone through the cement reflected off the formation all through solids and the final one is coming through the liquid inside the casing down along the side of the tool itself traveling through liquid which is slower so this is time you get casing formation and fluid and we will use that to interpret the log so here's the log the great thing about the log it is simple there are only five curves to look at and we really want to focus just on one curve so what are the five curves we have the dark line there on the left and i'll break it down this way this is where you can see the header the dark line on the left right down the middle is the transit time and we'll look more at the transit time in a bit when we fire the sound how long does it take to hear it at the three foot receiver the green line is the gamma ray we run a gamma ray it just tells us the natural radiation of the formations it tells us what is a shale and what is the sand or limestone the other hashed line is the ccl the casing collar locator it is a magnet basically that's picking up large masses of steel at the collar connections where joints of pipe are connected in the middle and we won't get too advanced here we'll get a little advanced when we look at interpretation but in the middle is the amplitude now if if you've interpreted bond logs before or if you've learned about them you will find that most people interpret a bond log by looking at the amplitude the amplitude is how loud the sound is of that first arrival that's coming down the casing is it the ring or is it a very quiet sound and i will tell you now we at thoroughbond do not use the amplitude to interpret we refer to it we know it's there but we will not use the amplitude and we'll talk about amplitude a little more matter of fact we have a rule at the thorough bond here's the rule don't hurt yourself when you apply this rule but but understand the rule if you start to interpret the log and you look at the amplitude too long maybe more than five seconds you have to slap yourself not too hard but just hard enough to get your eyes over on the final curve on the right and that is called the variable density log it is a depth versus time curve and these are the actual waves waveforms coming in let's look at these a little more closely the transit time is when we make the click to when we hear it at the three foot receiver in micro seconds for sound traveling down the casing it should be the same up and down the well you have the same fluid the same casing the same fluid the sound wave should always arrive at the same time that's if the tool is centralized in the middle of the well the amplitude is the height the strength of the first arrival there it is it's the height of that wave it's basically how loud is the sound that we first hear the variable density log we get the one wave at one depth we cut that wave in half it's like being in the ocean at sea level and the height of the wave there is the amplitude and i'm looking at one wave and i take that we're going to color those waves a dark color and we're going to look at just the peaks of those waves at one depth but now we're going to look and take that and turn it on its side where now we're not in the ocean we're above the ocean looking down on the wave and we're going to do that all along the beach or all along the depth of the well we're going to map the peaks the tops of the waves and then we're going to connect them all and when we connect them it creates the variable density log we will use the variable density log heavily to interpret logs when they're laid out before us on that table remember when you are looking at the variable density log and you learn how to observe it in that room everyone else is going to be looking at the amplitude curve and they're going to misinterpret again and again because they're looking at the wrong curve the variable density log every time you fly over the ocean and you look down you're seeing a variable density log with the receiver at the beach the transmitter out there and here comes the wave in the first wave that hits is that coming down the casing which it would be straight if it were coming down the casing so the next time you fly over the ocean talk to your spouse or your friend or and tell them look down there there's a variable density log down there on the ocean and they will be very impressed if you tell them that they'll be impressed for about a minute or two then that's all but you'll be impressed that the waves coming in we see those on the map and that's what the variable density log is so here's the cbl let's quickly review there are five curves i remember the first time i saw one i was on location the company man the well site supervisor said hey harris here's a bond log what do you think and what i really thought was i have no idea what i'm looking at i was a cementing person and i didn't know how to judge the cement job and you feel very foolish at that point and you promise yourself you're going to learn the bond log the great thing there are only five curves the dark line on the left what is that the dark line on the left we have three curves on the left track and different logs they'll place them in different places but this is very uh common to see it's the gamma ray the dotted line next to the gamma ray if you can see that it's straight in most places what's the dotted line it is the transit time hashed line what is that the hash marks next to this we will use it to help us interpret it's the casing collar locator in the middle there's another line there next to the depth that's the wire line tension in in pounds of pool but then we go to the middle curve and we have the amplitude we have two amplitudes here one is called the amplified amplitude it's on a scale of zero to ten millivolts and then the other one is from zero to a hundred same curves but different scale and then the final one on the right that we're going to use to interpret is what is the track on the right that is the vdl those are the five curves that's all that's there to look at now you'll get all sorts of curves on some other logs and you have to kind of uh sometimes they'll run a couple different curves here and there but these are the five basic you'll see all the time when we look at the vdl we want to identify the part of the vdl where the sound is coming down the casing it's the first arrival and we're looking for straight lines do you see any straight lines we do not see any straight lines because there is no energy coming down the casing this is a perfect cement job the next part of the curve we look for are formation signals we see the curvy lines because now we have differences in the formation as far as the speed of sound through them and then we don't quite see them here but you can usually see them and those are the fluid arrivals we have radial bond logs and the only difference is a radial bond log very quickly is a bond log that's the bond log those those are five curves and then we have eight receivers usually around the two foot or three foot receiver that are listening for one side of the casing and the amplitude is mapped out so you get a map around the casing now so that we're trying to pick up channels and we see this cement map which is a color coded a color-coded amplitude chart in this case we see the white you see right down the bottom of the casing this goes from the top of the casing down the bottom and back to the top i'll show you some examples and what we look for when we look at cbl results here are some cbl's we'll look at free pipe and that means there's no cement we'll look at a micro annulus which affects maybe 70 80 percent of the logs that you will see are affected by a micro annulus there is cement but it's been de-bonded we'll look at a channel and that is where either mud or gas or water has come in or has been left behind when we did the cement job and now we have a defective cement and then we'll look at what we hope to see as cementers and that is a perfect cement this is free pipe how do we know it's free pipe all of the straight lines means the sound is coming from where where is the sound that we clicked and we're listening for where's that sound traveling through they're straight lines they're traveling down the casing so you see those lines as we look at the vdl those big straight lines that's not good what we also see on free pipe are these color chevron patterns we call them big ringing patterns they are caused at joints where there's a slight gap between the steel joints it distorts the response and you get these big chevron patterns for a micro annulus it's a little different you don't always get the big chevron patterns but you see the straight lines first arrival it's the first part of that vdl straight lines that's energy coming down the casing that's not good it means there's no cement but but it's not free pipe in this case it's just slightly bonded you see a chevron pattern but it's distorted and it's dampened whether this is a micro annulus or a channel because channels can look very similar you have to use your interpretation skills which we'll look at in just a bit you also see those curved lines what are those where is that energy coming from this is the area where we pick up the reflections off of the formation so we know we're connected to the formation it must be cement but why all the casein ring well it's de-bonded so it can still ring it can still resonate and we can find channels and this is what they would look like once again we have casein ring first arrival if you ever see that on a log that's not good you're going to be gathered around that table and people are going to be debating what do i have well we happen to know here because we get a radio log and we know more about this well because this well actually flowed after we cemented it you see the collar is ringing now this could look very much like a d-bonded casing but now we have the radio which shows now there's a big a really big channel traveling through that i can pick up little pieces of formation those crooked waves but that big channel tells me what's going on it happens to be connected to a water flow that we recognize in the well and then perfect cement no straight lines a bunch of curves it will look like the open hole sonic log as if there was no casing in there beautifully cemented that's what we want to see nice formation signals all formation no straight lines this is the open host sonic this is without casing in the hole that's what we want our bond logs to look like the cement packed in bonded to the steel bonded to the formation so that sound waves travel through everything and just reflect off the formation what about this one see we haven't even learned to interpret yet and you're going to interpret this log do you think we have cement here we know it's not really pretty because see all the straight lines we don't want straight lines we don't want straight line first arrival we don't want casing collars shining like this or the chevron patterns but what about this what is this they're not straight anymore and this is where we have to interpret and we're going to let you interpret a log in a bit but when you see something like this you have to start an interpretation it's not so clear if you look at the amplitude it becomes more clear and i told you not to look at the amplitude for more than five seconds but you can look at it for four seconds and see that the amplitude is so high it actually matches free pipe amplitude as if there's no cement there each casing size has a certain free pipe amplitude that we expect so we have to investigate further when we interpret this we ultimately find out all of the sound coming at the same time this is a time curve as well occurs at the same time and what is happening here these are the last things to arrive sound waves down the fluid that makes straight lines distorted so this is free pipe we i know this well very very well and this is free pipe very quickly before we look at interpretation we're going to switch over and look at the ultrasonic log this is a very useful log this is the schlumberger use it log and people have different names for it but it's a pretty good name because you can really use it i receive into my office about two or three bond logs every week and when i receive an ultrasonic log i'm very pleased because i know it's going to help me interpret the log better so let's look at the ultrasonic the bond log is in the background in the foreground here is our ultrasonic it has a rotating head that hangs off the bottom of the logging tool and now we're going to spin this tool around and we're going to check out all around and really look for channels no longer the sound going in all directions or just listening in certain spots we're going to go around and we're going to be able to pick up every five degrees what's behind the casing now this works differently it's spinning seven and a half rotations per second and it's sending a sound wave out only this is a sound wave you cannot hear it's an ultrasonic wave at two to seven hundred kilohertz it's like taking a tennis ball and i actually have never thrown a tennis ball online and i don't think i will but i'll act like i throw the ball and i'm going to throw the ball against the wall and i throw it and then i catch it back so i throw the ball and i catch the ball back i send from the same transmitter the transducer becomes my receiver so i pick up one sound wave but what i pick up i pick up the sound wave and i pick up the resonance behind that sound wave let's take a look at it i'm taking it and i'm spinning it around and i'm throwing the ball and i'm catching the ball and when i get that resonance wave back if it's dampening and getting quiet there's cement if it's loud making a resonant ring then there's no cement it's a pretty neat tool i throw and receive i look at the first arrival let's call that ring and then i look at the resonance window how is it resonating how is the casing or the glass vibrating on the desk as the plane goes by from that resonance window i will gain something called acoustic impedance which is the velocity of sound through a material multiplied times the density of the material all matter on earth has an acoustic impedance and we're going to calculate what is right behind that pipe so we take that sound wave we take the resonance that's ringing between the casing and look at the wave we get back to surface we send it out and we get one big ring and then we get a decaying or dampening resonance window and from that i can learn about the casing radius we also use this as a casing inspection tool i can learn about the casing condition how it reflects off that casing by how fast i get the resonance window i can tell you how thick the casing is and by how it dampens i can calculate what's behind that casing it is a highly processed wave and i have thousands upon thousands of these waves that i'm picking up all around the casing it's a great tool this is what the log looks like and i won't go through uh the entire log at times you will get 38 45 pieces of information on these logs sometimes i think they put all that on there just to confuse you but we will use parts of it and we will use parts of it to interpret the log correctly first we have an eccentricity curve it can tell by checking all of the waves around if i'm centered in the well there's an amplitude map it tells me about the first arrival that reflects off the inside of the casing if there's a hole in the casing it will show up here if there's residue on the inside of the casing it will show up here we get the radius of the casing we can map the radius we understand the thickness of the casing we have a bond index which graphically shows how much solid yellow liquid blue and gas red and then we get the cement map this is telling us what is just behind the casing is it high impedance cement low impedance water or mud or is it very low impedance which would be gas the reason we use this tool is to be able to look all around the casing and find these kinds of channels what do you notice about this channel that i've circled it's not a straight channel and even if you poured water or a fluid onto your desk watch the pathway it takes it will find the path of least resistance it will meander like a river and that's what we see here this is a well leaking after the cement has been set between the casing and cement we have a path and we're leaking in this case probably gas through a water channel here's another picture of the ultrasonic when we get good cement jobs and this is a good cement job we can actually see a picture if you look on the right that's a picture of the casing laying in the wellbore the green is where the casing is touching the wellbore we get a beautiful picture of what's going on the only drawback that we continue to work on from a technology standpoint we're just seeing just behind the casing we're not picking out too far beyond the casing cement interface therefore that gas channel that you see here and this is a well that was abandoned in the gulf of mexico the casing is not centralized but we have a beautiful cement job except for a big mud channel and a gas channel that has flowed this well had a gas channel for the life of the well there was gas flowing through the surface that had to be managed currently we do not have technology that would be able to find that gas channel although we would be able to tell a channel near the casing okay that's the basics of the bond log and the ultrasonic log so how do we interpret them because what you see on those logs aren't always what you actually have and we have to interpret the bond log let's show you how we do it we do it by something called the five c's and then we'll go through a practice interpretation after we go through the method and remember the 6c is the coffee if you're going to interpret relax spend 30 minutes drink the coffee you'll observe a lot of great things if you drink five or six cups of coffee you'll really see things so you know somewhere between three and four cups is probably all you need to have and here's what we're going to do we're going to construct the well we have a saying let the wellbore interpret the log before the log interprets the wellbore another way to say it if you pumped no cement into the well then do not make an interpretation that says i think i see cement in the well it's not there so constructing the well is very important i'll show you a quick way to do that compare sections of the log these logs are relative a lot of ring not much ring no ring we we compare parts of the log i'll show you how we do that where we have changes as we compare we correlate when we compare we look up and down when we correlate we look left to right number four and this is the tricky one in the world of cementing where i come from in the world of drilling there are about 20 to 30 things that happen out there that confuse the log we're going to look at a few of those but this drives logging people crazy my log says this you're telling me my log is lying no i'm telling you the wellbore has done something and he's trying to trick your log so let's consider that i'll show you the considerations we have and finally we conclude at thoroughbond we conclude by saying here's what we got and here's why we got it and to know why we got it you have to know cementing okay let's get back to the family from the wisest to the dumbest and remember one thing you walk into the room it's time to interpret are you ready you better be ready because someone is going to be so loud they're going to say i've got the interpretation they're going to be wrong and you're going to say wait a second i attended a webinar and i don't think you know what you're talking about i i don't know if i would put it that way but i would say let's quiet the room it's too noisy so before we start let me ask a few questions here are four critical questions you need to ask on every log if nothing else it will quiet the room oh wow someone's asking a question let's let's see what the answer is as we're asking these questions what are we doing we're constructing the well where was the cement supposed to be you say it's a good bond log what if i tell you we didn't pump any cement then you're going to change your interpretation did we have losses or flows if we place the cement there are we sure it's still there an important one do we have a weak bond maybe it's a microannulus just i want to know did we do anything that may have broken the bonds and finally if we have a problem it's probably due to a formation formations take cement they flow into cement and so i want to know a little bit about the formation so here's the well bore i have to construct step one here's an example of a log what do you think about this log the coffee is a necessity someone once told me you shouldn't drink so much coffee while you're giving a presentation i really don't want to come what you speak while you're drinking coffee and i say i have to i'm sorry we're looking at bond logs do you like this bond log is this a good cement job we needed cement above this sand this is our secondary production do i have cement i have very high amplitudes these are free pipe amplitudes and then i got some formation but it looks bad a very big logging company came back and said we have no cement and i said well are you sure the exploration department was not happy drilling why didn't you cover this sand i said well let's construct the well before we get too excited did you know that we only pump 35 barrels of tail and it perfectly matches here i think what we have i may be wrong but as i construct the well i think we have lead cement because as a cementer i know leeds sometimes gives us bond so poor it could look like free pipe so we construct the well and i say hold up i think we have lead cement but let's interpret further i also am constructing the wellbore i'm looking at the lead tail cement what else do i look at in the wellbore i look at the casing it will affect my logs i look at the formation on the gamma it will affect my logs i then compare log sections that's pretty easy to do i've got good down below even though i've got straight lines that's not good they're low amplitude i've got strong formation if nothing else this is much better than this up here so i compare those sections and i kind of put a thumb print or a fingerprint on those sections i've got my tail and potentially my lead my tail my lead that's what they look like i then go to compare my lead with what may be free pipe compare those two and this is where you use your skill of observation do they look alike if they don't there's a reason they don't look how much the top looks like free pipe this is on the same log up higher where i expect free pipe and look at my tail cement i'm sorry my lead cement down below it looks different if i were to compare the two i'd say the upper is all straight lines i get formation down below and something's going on we actually ran a temperature log on this well and we found that this was leed cement we found cement up higher we're showing here at 5500 feet we found top of cement with a temperature log at 4500 feet but i compare that and now i look for changes and this is a different log but we then correlate step three so i do my comparison i'm calling this good bad good if for no other reason look at all of my bright straight lines and i have to figure out why is this bad and so i correlate i correlate at the points of change and you can see these as you observe i say let me correlate to here and here and i find that i'm correlating to collars to gamma mainly i could correlate if this were a cement change it's not i could correlate to my cement like i did before step four and then we're going to interpret a log you are now almost an expert log interpreter here are 20 i could give you 35 key factors that affect the log that drive the physicists a little crazy who have developed these great tools i'm just going to show you a few but here are the 20 top issues that affect the log let's look at a couple of those the first is new casing i'm showing here 62 millivolts amplitude that is free pipe for seven inch casing and this happens to be seven inch casing in a well in cutter this is in cutter in the middle east the vdl shows a lot of bad cement but it shows some formation signals straight lines and crooked lines what's happening here we did four wells like this with new shiny casing shiny casing does not bond to cement and can give you a bad bond log we have to consider that so what do we do we sandblast the casing make it rough no longer shiny and look what happens here we do it for a couple joints of casing and the straight lines go away new casein can confuse the bond log that's one consideration i always make lightweight cement the lighter cement the more the casing will ring when i hold this glass to stop the ringing from occurring i can't do it barely touch it it still has some ring to it i have to hold it tight and i do that with stronger cements so lightweight cements will affect the bond log it confuses the bond log here's another one that confuses for the good this is an uncemented well but we have shale that has swelled and has collapsed around the casing and is now providing bond probably better than cement so we have to understand that shales bond goods sandstones bond poorly and they try to confuse the bond log we have to consider them here's a big one this has affected so many wells around the world when we pressure test casing we tend to stretch the casing and relax it we start to break the bonds the bond log on the left do you see any straight lines look for those straight lines we have the gamma hard to see the transit time the casing color locator the amplitude the amplified amplitude and the vdl maybe a little line here but this is a good bond log all we've done is pressure tested it to 3000 psi we rerun the bond log and look what we get straight lines we have broken the bond now if i run the log after i pressure test i think i may have no cement or a bad channel when in fact i just have a confusing log due to lack of bonding these are the kind of considerations that we have to make look at these two logs another consideration is cement shrinkage when cement sets it will tend to shrink during the hydration process so we put expansion additives in to make that bond tight look at the log on the right that's a great cement job versus the log on the left it's not bonded well something more important than that you got a beautiful bond log on the right but we have 15 wells like this and they are not leaking gas we have 30 wells like that one on the left the bad one and they're leaking gas they're percolating gas they look like this i don't know if you can see it but this is gas percolation we call it a vent flow it is occurring between the surface and intermediate casing because of poor bonding that's all that's happening number five it's only five steps and it leads you to good accurate interpretations you have to conclude you know when you're in that room and it's noisy i don't know if you've experienced this either in your work or in classes but someone usually speaks loudly and speaks too soon and you maybe being technical you want all the data so you're not saying a word you're just collecting the information i'm gonna think about this and you're not saying a word you don't want to be wrong and you're a bit introverted you're not going to be loud you're not going to say i know the answer is everybody be quiet you're going to be thinking gathering all the data but remember this you're going to have colleagues who are going to be loud and they're going to say i have the answer and if you say nothing if you're still thinking it's probably better to speak up and be wrong than to never say anything so we have to conclude sometimes we have to conclude with little information hopefully we have more information understand this this should be helpful these are the only eight choices in the world of oil and gas cementing that you get there are some good things that can happen you can have good cement bond or as we saw with the shale maybe it's not cement maybe it's shale good geologic barrier a shale bond do i have zono isolation or not i don't know for sure it might be a weak bond but still zono isolation it may be one of those micro annulus we talked about the debonding or maybe you're going to have a great bond but the cement just needs a little more time maybe you have to wait on cement longer those are questionable the bad results are you have no cement at all all this meant was lost or you didn't lift it high enough or you're flowing from one zone to the next you have cross flow or you have channeling that channels all the way to surface or maybe it's mud left in the hole that now is providing a leak path and now you're losing production or you have poor well integrity because of channeling those are your only eight choices and we got to pick one of those but we also have to understand why and then we can make our conclusion in our final step of interpretation okay are you ready to interpret a log and we'll spend the next 10 or 15 minutes allowing you to interpret that gives me the chance to be quiet to finish my coffee and to let you be the interpreter so we're in the room we laid the log out and here it is i'm only showing you a section of the log you walk into the room it's noisy what's the first thing you're going to do what is the first thing you're going to do you're going to smile you're going to be friendly and nice what is the first thing think about the interpretation method what's the first thing we're going to do i have to take a peek at the chat there we go we're going to construct we're going to construct the log and i feel when i see the chat box i'm with i'm with a good bunch of interpreters so thank you we're going to construct the well not the log the well so that's what we're going to do i can tell you the first thing i'm going to do how am i going to construct it what's the first thing i'm going to do it will help quiet the room as well what will you do because you know what happens what happens is that you go in and you don't have all the information often we're asked to interpret the log without sufficient information you just get the log here's the log i remember receiving this log it landed on my desk and they said interpret the log i knew nothing about the well so what do we do i don't know if you've ever used the chat feature on zoom but if you use the chat feature you can send me a note and tell me what the answer is we're going to because i see the hands being raised we're going to ask the four questions let's ask those four questions we're going to get to your point amara we're going to get to your point because that's an important one of where is the interest zone or the zone of interest we're going to ask those four questions where was the was there a lead entail this is to quiet the room and to construct the law the well we're going to keep we're going to construct it first yes there was a lead and a tail and we'll talk about the log scales in a bit thank you well there was a leading entail but this is all tail this is all good tail cement with their losses or flows no there was not okay what about the casing is there a reason that the casing might be debonded not that we can think of is the answer but look at the log a lot of the casings are bonded but i'm still thinking that maybe some of the casein joints de-bonded and what about the formation of interest and the drilling engineer told me i'm not sure just can you please interpret the log and sometimes that's what you get and the log scale the only log scale i would say that we need to know at this point to interpret this log is the amplitude there in the middle is from zero to 100 millivolts this is five and a half inch casing so free pipe although we don't see it here free pipe should be out here at 72 millivolts but once again listen to me we don't look at that amplitude for four seconds that's all you get we construct the well what do we do next after we construct the well muhammadu says it thank you segment we compare so let's do it very quickly this small section is easy to compare you've got good you've got bad and you've got good we want to know why is it bad is it bad first of all really or is it just looking bad and why is it bad that's where our interpretation needs to take us do you think we have cement here just looking at this do you think we have cement when i look at it i say yes i think we do but now i have to do the interpretation and so let's keep looking what do we do after we compare this is where we get into the heart of interpretation comparing is sitting back and looking up and down the wellbore that's where you have the coffee you relax and you look up and down the wellbore where is it changing where is it changing and you mark those spots this part of the log was quite evident this is our problem section and so that's why we're looking at it i like this i'll put on my glasses and check who said this habib says new casing joints may have caused bad cement in between you are going to be a very good interpreter now i'm not saying you're right but that was my first thought as well but let's do our next step it is laura bell mentions it so does dan let's correlate to correlate i'll just draw a thinner line instead of up and down we look side to side and i have to understand how important these correlations are do you see where we correlate we correlate we want to correlate back to the wellbore that's formation casein cement remember i said all of this is tail cement so there's no correlation to be done there so i look at casein habib you might be onto something do i correlate to casein or do i correlate to formation this is where correlation becomes very important when you learn to interpret logs you will correlate all over the place you'll start solving and piecing the puzzle together and to be honest it's a lot of a lot of fun where am i correlated to maybe this will help we also had thank goodness and ultrasonic for this log so we just kind of started interpreting the ultra the the cbl now let's go to the ultrasonic sometimes when you get the ultrasonic you don't get the full log i wish we always did but sometimes we just get the map and the gamma and the casing collar locator correlate for me does the change occur at the casing collar if so habib i think you're on to something big and i'm right there with you or do we correlate to the formation which is it what do you see at this point in the interpretation you have quieted the room but i don't want this room to be that quiet right now where are we correlating to we have the casing collar locator you can see the casing collars here the black lines over here is the gamma do you see the gamma am i correlating to the collar or the gamma correlating to the formation thank you ayush we're correlated to the formation let's look back at this log look here look what we correlate to you see the gamma spike what is that what is that gamma spike i'm correlated to it i thought i was correlated to the casing when i first saw it because remember 70 80 percent of bad bond logs are poor bonding thirty percent are poor cement jobs so i'm always thinking bonding how bieb was thinking bonding i like that but it's not always the case is that a shale looks like a shale to me the problem is shales bond good only marwa i'm not sure it's a shale so let me go to the drilling engineer and i say what is that and he says looks like a shale i said yeah it does but what is it he said i don't know let's go talk to the geologist so we could go talk to the geologist in oil companies the geologist or petrophysicist usually is the go-to person for bond logs they are familiar with the bond log they're familiar with case total sonic and open host sonic and they're your go-to people they also know the formations and formations affect logs all up all over the place up and down so if you do not know a geologist get to know one buy them lunch once every month be a friend with a geologist if you're a geologist you need to also find a friend so they will buy you lunch i go to the geologist he says that is a hot dolomite it's a dolomite it's a hot dolomite this is all carbonated but we have a few little hot dolomites where we have injected co2 into and now we have radioactive hot dolomite scale that's being picked up he said i'll tell you more about this formation kirk he said do you know that we are injecting into that formation right now that formation is probably 200 psi over pressured with co2 injection i go to check you know what i find out while we were cementing we were injecting into that formation in offset wells i now am no longer thinking about law i'm thinking about the wellbore this may be no cement at all here look at that it's being washed out i have no cement from the gamma i may have a big problem knowing cementing understanding cross flow i now know that i have cross flow between a hot dolomite and a normally pressured fractured dolomite and i've wiped my cement job out that becomes my interpretation am i right am i wrong i don't know that's my interpretation that's as far as i can see what you're seeing but i've got the construction the comparison i correlate i considered the casein being the problem but i have to conclude so we go in and we perforated right here and we perforated up here and we circulated at eight barrels per minute we had pure circulation all the way back to surface we did a circulation squeeze and we sealed off that area in the next two wells now that we know what had happened we actually used an external casing packer to cement those wells take a look at this here was well one we just interpreted that look at well number two this is pretty cool well number two we put a packer in there because we didn't want cross flow we need those to be separated because this is controlling our injection profile so well too do you see on the ultrasonic you can even see where the packer is oh it's a beautiful cement job this right here is that other fracture we can even see the fractured fractured dolomite we do the same thing on well number three on well number four we made sure everything was normally pressured and we cemented it without a packer but do you see what we've done we didn't say good or bad here's your log we said here's why now let's look how to correct the next well that's the beauty of the bond log we're not just going to analyze the well we're going to fix so well after we fix the well we're going to cement the next well better so when you run into somebody who says you can't trust bond logs i don't like bond logs when you run into the grandmother that says i hate them understand they are extremely useful and it's very very beneficial for you to learn the bond log we'll close with just a quick story this is out in west united states out in arizona my son he likes to uh he likes to hunt animals i hope that doesn't offend anybody he likes to hunt the deer i don't i don't do that i don't have a gun or do any of that but he likes to and so he goes out and he's out looking for an animal a deer and he never can see them he says it's very difficult i can't find any animals to hunt so he goes out with an expert hunter and the expert finds the deer here's my son right now looking down at a deer i can't see it he can barely see it but the expert says there it is and my son seth he said to the expert i've been out with you several times i can't see anything how can you see them am i blind and the expert said no you're not blind you're just inexperienced i know where to look i've done this for so long i know where to look i know how to look i know how to see the changes when you go through interpretation you have to keep at it and keep practicing and there's a wonderful market where oil companies and service companies need your services to be able to interpret these logs and so he said keep looking keep looking for the deer and you will start seeing it the same is true with the log and i close with this this is a copy of a bond log on the left and ultrasonic on the right when i look at a log i try not to see and i often don't see the crooked lines the straight lines the colors the patterns what i see as i look at the log i see the well bore that's what i want to see i want to see the cemented well and here we have it and i show in this slide 20 places that i look to find certain things i because i've looked at thousands of logs we see the same things on log after log and we learn the tricks of the trade how to observe the deer and the brush we learn how to observe for example when i go to number five i look for that i look for dark spots to know what my casing condition is when i look at number two up there in the upper left-hand corner i know that at a previous casing i will be given some signals on if i have cement or no cement at the previous casing and so i encourage you as we close i encourage you to keep looking at the logs and the more you look and the more you start understanding why the patterns you see are the way they are the better you'll get at it i want to thank you for the opportunity to talk to you about the basics but also the method we used to interpret the logs if you have any questions uh i will now pass it over to our moderator thank you so thank you engineer harris for this informative and distinctive lecture uh i'll begin by the questions so the first question is that can we calibrate tools in double cage and how calibration and double cage affects the cbl or ultrasonic great question it's about the calibration of the tools what we normally will do i was visiting the schlemmer j shop recently they will function test the tool to make sure the transmitter receivers are working there are some companies that can calibrate in in the cell but things change with pressure and things change with different casings often we do the calibration we won't call it calibration we'll call it normalization in a free pipe section in the actual well that's being run and so we'll do some calibrations on site each company is a little different i was looking at some logs recently in the north sea and these are old logs and they're uncalibrated uh logs so the amplitudes are too high and some things but we can still interpret the logs because as long as that tool is centralized and the tool is functioning although i don't have absolute correct numbers i can compare parts of the log so even poor calibration may not stop us from interpreting most are normalized on location but definitely several tools are calibrated in the calibration well at the various sites okay thank you another question is that if there is cement and severe washout how bond to formation appear as a function of tool depth of sophistication well these are good questions yeah when you have washout and often you'll see a washout for example right past the the previous casing you'll get a washout that was in a rat hole area or in that that zone you'll see the formation signals slowly disappear just because of the borehole size if you see formation disappear you're either washed out or you do not have bond to that formation or it's a shale the shell has come in and now there's no formation to go to because the formation is already there so in washouts we can pick it up by watching when the formation arrivals change and we do that quite often that's a good question but we see washouts on that vdl thank you uh and finally the last question is that um if shale swells and washouts mainly occur at all the this type of formation why does it make it a good bond while sands which are considered more stable or has higher strength but make it a bad bond boy if there was a question of questions that's the question excellent question from the shale standpoint although you can wash out shales think about even oil-based muds where you don't wash out the shells but when the shells are coming in they're coming in so the bond is good because they are packed around the casing there's no longer a washout they have actually collapsed swelled and are wrapped around the casing matter of fact they are pretty good bonding materials because they reconstitute themselves once you break the bond you break a cement bond it may last forever the shale will reconstitute and heal itself the reason the sands are bad are for two reasons one fluid influx coming in it's real i've seen many bad bond logs and many bad cement jobs because the hydrocarbon comes in and contaminates the cement the other reason is because they're porous quite often and you have cement around the casing but around the cement you have formation and if it's solid rock like a limestone great bond if it's porous then it's poor bond we often also see channeling in sands so they look bad but the shell next to it has collapsed and there's no more channel so that's why we get sands are bad shales are good on most logs that we look at great questions so thank you engineer harris for this informative session and i want to highlight that this session was being recorded and it will be uploaded on pi petra's youtube channel and also we will be holding also uh webinars and short courses for the upcoming months so please visit the arab oil and gas academy facebook page uh to check the schedules of the webinars and along with the topics which will be presented and please try to register before the deadline now i hope you have a nice day and see you in future webinars thank you thank you very much