Introduction to drill core and core logging

hi there let's talk a little bit about drill core my name is Dale Sims I'm a geologist live listen they from Newcastle I'm here at the University of New Castle's core shade which is the cocoa closest place to where I live where I can get my hands on some core so this is an introductory video really just to help people who may be attending the five-day core logging of course we've got running in Brisbane the eyes I'm Mei Jia initiative and that's an introductory call log in course but I wanted to give some video support to people attending that course so they get some of the basics perhaps before they even arrive and these are for people who haven't had any exposure to drill call or log in before not seen any core or may not have seen a jewelry so it's very introductory so drill core is a tube of rock it's a tube of rock that's drilled mechanically by a machine called a drill rig and the drill rig produces this core from a drill string that's spun by the rig and advanced into the ground and on the end of the drill string is a barrel and on the end of the barrel is a bit and the bit has diamonds in it and the diamonds where the rock away as the tube of rock sorry the tube of steel the string or the the rod string spins and the core is advanced up into the inside of that spinning tube of steel very simple really and then at certain regular intervals the drilling stopped a tool is sent down the middle of the tube of of steel the pipe the drill pipe of the rod string and the core inside is recovered and that's what gives core that sits in trays like this so we drill a lot of core in the minerals industry and so this is to help you understand what can we do with it and how do we approach trying to understand the drill so here is a tray of core just a single try on its own if you lift it up you can have a look at it it's got two rows in the tray and the rows are filled with this tubular up the drill core and the tray is red just like the pages of a book the writing on the pages of the book so we start in the top left hand side for this particular tray that's the start of the length of call that's been put into the tray and the bottom right hand corner is the end so the core is read from left to right advancing in trays in the rows of the tray down from the top left to the bottom right as I say just like reading text English text perhaps in in a book and so first thing you got to check when you're looking at core is other trays around the right way normally they have something written at the start of the trade normally they have start written at the start of the tray and that tells you that that is the sound of the tray is that greater than the end normally they write end which is fantastic so logical I don't know why it so hard anyway so we read the core in runs and then we observe the geology that the core contains that's the whole reason we're drilling the core is so we want to see what the rock is so the minerals industry drills on a lot of core that's all I'm to try to understand what is the rock that the drill hole is intersecting the hole was drilled in that position to get information about that the rock in that location that's not only reason this beam drill I don't think so inside of the trays we find things like it's called core blocks and the core blocks are put there by drillers I want to talk a little bit about core blocks and what they mean and what do we do with coal blocks okay so this block it's got some writing on it or core blocks have writing on them that's why they're there in the tray the reason they're here is is this has been the end of a run this is where the length of the drilling where the core has been drilled by the drill bit and moved into the barrel at the bottom of the drill string that length has been has rather reached its maximum so the barrel is full and needs to be emptied or alternatively there's been a problem with the rock and things like maybe broken material has wedged sideways into the metal tube which is the barrel and it's blocking the core from going further up into the tube either case knee means that the drilling gotta stop they unscrew the drill pipe they put a tool down and they recover the core from the bottom of the drill string from the barrel when they do that the driller writes a block to show what is the depth at that point where the drill has been stopped and the core has been extracted so what we want to know this block tells us at this particular point what depth from the color of the hole or the surface what depth is that is that position and here the depth is thirty nine point five five meters and the driller has said they've drilled a length of 3.00 meters and their recovery is three point zero three meters so their measurements show they're recovering slightly more core than their drilling is that possible it's not possible it's showing that there's an error in core logging and core measurement and error is a real issue that we've got to deal with whenever we look at your core because it isn't a precise science there's imperfections in the system and one of them is this issue of measurement so the drillers drilled three meters he knows that he or she knows that from their machinery but the recovery has been measured on the drill core if it's put in the tray and of course the core has been open it's been shaken out of a tube we built it with a hammer to actually to get it come out of the tube and so rocks that are very weak and friable a bit like these ones here this little shale band those rocks can break up and when they break up they occupy a bigger volume than they do when they were originally in the ground so that can lead us to recovery where we're actually getting more length than what we're expecting to get from the drilled length we put that back before I lose it so drillers blocks are written by the drillers and placed by the drills into the core tray they're not always right drillers blocks can sometimes be an error or talked about it in a minute so we've got two blocks here there's a block at this position in the drug war and there's a block here at this position the drill core this one says 45 point five five as the depth from the surface this one's forty eight point five five so the driller has placed this block when they had drilled the previous run and then when they finish drilling this run they placed this block at the end of the run so the block is always placed at the end of the run that's when the driller has the opportunity to measure the depth of the hole so this is saying this position here is at forty five point five five and was after they drilled a three meter run and recovered two point nine eight meters now three meter run is the standard length of a barrel three meters is what a barrel will drill on its own and this rock is extremely strong when you look at it it looks like concrete this is a conglomerate you can see the rounded class and it's a very very strong effect they've got to break the rock to get it into the trace it's that strong not all rock is that strong anyway so this is the block from the end it's saying that they've drilled three meters and their recoveries 3.09 meters now they know what they drill because they can measure that on their machinery through measuring a thing called stick up and then knowing link that they've advanced the drill pipe through but how do they measure recovery and how do we measure recovery to check the drillers values because we don't want to just be taking the drillers values on face value we want to measure that it's ourselves you want to check their distance so we use a tape measure a metric tape measure a steel tape measure and we start at the beginning of the run immediately below the previous block and we'll measure out to the end of this run with the core sort of push it up nice and tight we can hold the tape there with our fingers grab the same position come to the next run measure along do the same thing hold the position there measure along to the next month hold the tape there and come and measure the last one so I get three point zero six meters three hundred and sixty centimeters 3.06 meters the driller measures and got 3.09 now is that difference significant not really you know the core does move around a little bit it doesn't always match or mate perfectly in the tray but it's really showing us in this rock we're recovering just about all of the core that we're drilling in that run and it's because the rock is so tough so not all raucous like this like this is coal I don't do any car work but I wish I did now when I see rock that's this tough very very strong right so we're talking about the purpose of drilling core is is to understand the geology of the area there the holes being drilled of course really we're trying to understand what are the boundaries and one of the rock types within those boundaries so it's about context it's about developing an understanding of domains so here in this core we've got the gray concrete looking Rock and I'll give it a squirt so we can actually you might be able to see it a bit a bit more clearly it's very beautiful Rock conglomerate quite it's quite a problematic rock for coal because it's very strong coal mining normally wants particularly coal mining wants rock that's gonna fall down after the coal has been taken out so we can see here the conglomerate continues up to this point and then we get a different rock so this is where the the coal or the FIDIC shale commences it's a totally different color you can see and then further down we come back out of the coal and we go into like a pale grey fine-grained sandstone here so we've got some context we've got a contact here between the conglomerate and the coal or carbonaceous material and then we've got another contact in here where we come out of the dark material going into the lighter gray sandstone there's a further contact just down there where we go back into conglomerate so these contacts are what's important to us we want to know where are those boundaries so how do we know where the boundaries are well we can measure them once we've established the depths values of the drillers blocks and we do that starting at the color of the hole measuring from block to block to validate the numbers that the drillers have written on their blocks so remember there's the block there forty eight point five five so once we validate that we can use that block as a measurement point to measure any position further down the drill hole so if I take my tape and I'm and I want to measure from this position down to the start of that coal seam for example I can again use my tape measure right incremental e extending it and I get it to about 1.9 meters so we've got 48 point five five plus one point nine is fifty point four five I just have to yep fifty point four five so I can write that depth on my log now depending on how I'm logging it either on a computer on a piece of paper I'm just gonna pencil it in fifty point four five is the depth at that boundary when you look at the boundary go well that's a bit odd because look here's the contact with the conglomerate I can see it's actually at quite an angle if this hole was drilled vertically which is best just that all coals cold joint is then that contact is quiet at an angle it's not a horizontal contact it's like 50 degrees actually you can see it's got a little bit of shearing on so it's been that's made it worse but it's got some shearing on it little slickin lines it's feeling very smooth and graffiti that's a little false at contact there's been some movement on that contact point but basically here's our piece of coal there's our depth on it we can spin it around so now our depth was there from fifty point four five so there's a little bit of material being gone missing out of here we've lost some core and this is what happens in core drilling that material might have just crumbled up and washed out when the water flushing the drill hole went past the sexual position as it was being drilled we're reminding falling out when when the core barrel was being emptied or it may have been lost in transit at my ex he'd be lying around in the bottom of the tray it's just been smashed up because this rocks been transported so the principles are that once we establish the depth of the drillers blocks and validate the recovery then we can understand we can measure any point backwards and forwards between blocks for example if we if we validated this block is being three meters from this block we could measure that distance either from here or we could measure that distance from here it doesn't really matter if we validated the blocks as I said before you know all worlds it's all a compromise and often we get errors in drilling we lose core so here we'd lost a little bit of core in that in that little wedge we'd lost some of that material but we can actually lose large amounts of core we can use lose meters and meters of core sometimes you can just have two core blocks side by side they've been drilled three meters apart but there's no call between them at all because the cause been lost so core loss is another thing we need to deal with and normally the driller when they do their recovery they will notice if the recovery is less than the core length that they've drilled they'll know that there's been a loss issue and they'll go to try and find where the loss has been and they'll quantify the loss on the block and often they may say they might write on a block core loss just to highlight the geologists that they know they've lost some quarter so we're talking about these boundaries and the and the changes in the in the geology as we go down the drill hole so the logging process can have different purposes you may be interested in logging find detail not quite on millimeter scale but very fine detail in some areas it might be very significant for what you're trying to do ultimately with the data but as a first pass my advice is to step back and take a bigger picture view you try to find the main issues the main context so as we said before we had a contact with further up here we had a contact with between the conglomerate and the coal seam within the coal seam we've got little layers and penny bands or shale bands which occur within the coal seam very important to log the details in the theme itself will have importance for the for the quality of the coal and how it can be used once it's been mined but on a broad scale what we can see in the rest of the trade or the rest of the hull is is a lot of areas where there isn't coal and that we've got large amounts of conglomerates and sandstones sitting there the whole color of the of the drill trays is very much light brown sedimentary rocks so understanding where we've got from coal to find sandstone coming out of the sandstone again into conglomerate those major boundaries are the important points we want to get at the first pass the high-level logging we can come back and get detail but we may not want to get detail on everything we only want to get it out of a certain area so this is one of the challenges of core logging is understanding what is the scale you need to work in because you can spend a lot of time logging core collecting data which is really never really used much at all pick the bulk of the core data that we collect I'd hazard to say we don't use we don't use very much so focus on what's important so we just kind of have a bit of a Travis down this hole we're going to look for where the boundaries are so we're back in a conglomerate here you can see something blonde we see the particles in it then it goes back in the finest sandstone you're getting some gray rock here too so we're going back into some more well cold and refitting shales so we can see it's a bit like a barcode there is white and dark rocks spread through the drill hole so as I said before it's those boundaries which are really important for us to try and get recorded in our logging don't get bogged down in the detail but just before I move on to some other core this core size is HQ core so going from large to small chordoma what's commonly drilled commonly HQ is it probably about the biggest most times we drill there's a bigger size called PQ which is drilled occasionally but normally near the surface particularly through poor ground near surface more in Asia and New Zealand then in Australia but occasionally used particularly people want to get large sample volumes P cube gives core that's about 100 millimeters in diameter this is HQ so HQ core drills a hundred meter diameter hole but it only delivers a 75 mil diam at a core because the difference between the core diameter and the size at the outside of the hole is the thickness you need for the machinery that actually allows you to do the drilling the the what's called the kerf of the barrel so this is HQ the next size down is NQ n Q delivers 50 inch core from a 75 mil not 50 inch sorry 50 mil core let me try that again so the next size down is n Q and Q delivers a roughly a 50 mil core from a 75 mil hole and then less than n Q is B Q not commonly drilled from surface but often drilled underground or a variant of it may be drilled TT 46 and B Q will give you a call that's smaller again then NQ so all these core sizes fit within each other they're like Russian dolls stacking nesting and that's to allow us to drill holes to a certain point and then reduce to a smaller core size and keep the hole advance in particular when we have difficulty in ground this is a logging sheet this is typically what logging sheets look like this one's called coal log which is for logging drill core it's a table that's got the depth from in the two depth of the observation seam ply horizon so they are trying to identify which particular part of the stratigraphy you're working with and then issues around lithology to your technical mechanical sediment illogical and what minerals are observed so these are rows each row represents an interval down the drill hole and once the depth is established then the parameters can be filled in across the table to develop a database or a data table of information so it's very common that sort of approach to logging coal log is a industry supported logging standard very good system so that was we started off there looking at that drill core from the coal drill hole I felt distinctly uneasy because I'm not a coal geologist although that was my first job as a student for three months was logging drill core from Carl drilling but this was the core we were looking at there before this is the HQ sized conglomerate very beautiful rough made out of fragments riverbed material but let's compare it to this rock here so this is rock from a project in New South Wales called wooden Warren Woodlawn donated some core to the University here in a number of years ago and they use it in their economic geology logging exercise so the first thing I said is that this core is much smaller diameter so this was the HQ core this core here is BQ it may even be small in BQ I think it's an underground drill hole this could be what's called TT 46 which is even smaller than BQ again so different size cos and when you look at this rock it's quite a different type of rock the rock mass is very different remember when we looked at the core from the coal hole it was very solid they had to break it to get it into the trace is that is this core like that I don't think so this cause been broken up it's very fissile when you look at it it's got a lot of graffiti partings it's very deformed this isn't drill core from a coal prospect this is a VMs volcanic hosted sedimentary sulphide deposit and so it's had a hard life it's much much older and it's been through a lot of deformation and the mineralizing system actually introduces deformation and alteration is part of the process which affects the rock but the other feature is that the core is smaller diameter and core smaller-diameter core is not as strong as larger diamond of course so it will actually break up more in the drilling process particularly if the ground is highly stressed anyway the principles are the same we've got blocks here the blocks are little pieces of plywood cut up and they've got numbers written on them his 81 meters is on that block here seventy nine point three eighty four point four eighty five point two so those depths have been those blocks have been put in by the driller at those steps let's just measure it and see if we can validate those those that that distance the driller hasn't written the distance nor the recovery on these blocks so if it was right if that was seventy nine point three and that is in the right spot at eighty one and we're looking at one point seven meters of distance it's a measure so we've got about two point one meters of distance there so what could have happened why we were expecting one point seven and we've got two point one what's gone wrong okay so this core has been sitting here for a while it's been transported it may well be that that block is in the wrong space hmm that could be wrong but if it isn't what could if these blocks are really in their right positions where they were originally when the hole was drilled what could be the difference well you can see here we've got a lot of cause been moved you've got a lot of gaps so the core needs to be pushed up sometimes if it's important they actually rotate or what they call jigsaw at all together when you jigsaw the core together it shortens the length so if we fit all the core together it actually reduces the length so I think that's part of the problem we've got here so we've got more core than the distance that we measured so we were expecting one point seven we've got two point one so the cause been straying out now if for example we were expecting that distance of one point seven but we measured it and we only got one point four then even with that spreading out it doesn't accommodate for that shortening rather than lengthening of the measured interval and normally what that happens when that happens is you've lost core so the core has been ground away or been washed out or you've intersected a fault and the fault hasn't been able to be drilled by the drilling mechanism that's very common in deformed complicated mineral type or bodies normal to get caught off occurring all part of the fan so here's another example this is the Woodlawn drill hole as well now this is cool that's been you know gifted here to the University so it's its core that's already been through the mineral industries processes you can see some of its cut in half and some of its not so when the cause been cut in half it means that the half that's not here anymore has been taken and and ground up and had an analytical process applied to it to get the elemental contents of the core recorded so it's measured or its theorem what's termed essayed the core has been removed taken away pulverized and then tested with a series of chemical processes for analytical processes to work out the metallic content and that's important because this is a copper zinc gold silver mine and so they we need to know how much zinc copper gold silver lead is in it now this core is getting on in its age not all core cause normally very beautiful when it's brand-new but as you go on in time particularly if the constituents of the core cell FIDIC you get these rusty zones oxidation the minerals once they're exposed to I start to decompose and that D curve is that decomposition modifies their content and and the chemistry and often releases acids and things so the core sort of slowly rots and so when you log in core you get the opportunity to log it fresh when it's just been recently drilled that is the best chance you've got of seeing it nice and clean as the course it's around gets to the point where at some stage it just can't be used this isn't too bad we can look at the core and get understandings of where the sulfide zones are so we can see where sulfides are if I smell the core I can smell this smell of sulfur coming off the sulfide minerals and there's a hard rock undermining geologists that's what I love is what I'm in the business for but you can see the grounds quite poor it's been smashed around potentially a fault or broken grounding through the air so quite different to looking at the drill core that we had there before the other thing I'll point out is this funny little piece this little it's not a tube you see it's not quite a tube it's a piece of core that started off like a tube started off like this but then it fell back down into the hole and it's at the end of a run because it was a piece of call that fell out of the tube filled in the bottom of the hole and they got over drilled when the drill rig went down again to start drilling and Rickon and recommence the hole so it's a funny odd shape because it's been drilled twice and because been drilled twice I know it was originally above the block and so if it was located below the block that's the wrong place for it because it was originally a buffer block which is where it was here in the trace anyway I think that'll do I'm looking forward to seeing you guys on our five day core logging course I hope this might have been some help to you see the energies you

Channel: Dale Sims

Views: 36,689

Rating: 4.927393 out of 5

Keywords: geoscience, geology, core logging, drillcore, AIG, AusIMM

Id: qpQb7jaO5uw

Length: 31min 4sec (1864 seconds)

Published: Wed Oct 16 2019