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GEOL7324 Rock Physics - Day1 08-27-2021-Part2
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00:00 this conference will now be recorded. , so you can all see uh
00:13 full screen. Now, I'm on motivation side. Why is this important
00:20 us? So, I'm going to you a synthetic example from mike,
00:25 cell and Daiwa han. Uh This a synthetic cdp gather. Uh and
00:36 in particular, it had the normal out corrected. So here we have
00:43 receiver offset on the horizontal axis. have seismic record time on the vertical
00:49 . And so you see the longer source receiver offset, the longer the
00:54 time would be. But these events all coming in at the same
00:58 And that's because we've corrected for the . This is what we do before
01:05 . We do velocity analysis, we the events up and then we stack
01:09 together. And the reason for looking the gather before we've set. As
01:16 can see there is additional diagnostic information . Many of these layers have almost
01:23 identical response at the different source receiver . But this particular layer, which
01:31 to be important because it's a reservoir a big variation of amplitude uh with
01:40 angle of incidence or with increasing source offset. So, when you stack
01:46 , this variation is lost, all get is the mean amplitude somewhere in
01:52 . And you're losing that thing, can be diagnostic of hydrocarbons. All
01:58 , so this particular model, that had a V P V s ratio
02:03 vP. I mean p wave velocity shear wave velocity that ratio tends to
02:09 very sensitive to hydrocarbons. So that here is 1.83 in the reservoir
02:18 which is the sand And on either of the reservoir layer, it's 2.13
02:23 is the shell. Now, we're to vary the V. P.
02:28 . S ratio in these formations very . In fact, we're going to
02:33 down the V P B. S in the sand a little bit,
02:37 also in the shell, because very you get some gas in the shell
02:43 it's it's the PBS ratio of it to not just in your reservoir.
02:48 what is the response which we get we do that? In this case
02:54 get a flat response. This is to what people's expectation is. The
03:00 of thumb is when I have gas I have a low B P
03:06 S ratio, I have an amplitude with offset. But you see
03:10 we have a relatively high V. . V. S ratio. This
03:13 actually a brian sand that has an increase with offset. And when I
03:19 the V. P. B. ratio, when I have gas and
03:22 up giving me very little change of with offset. So one could,
03:29 this particular case, if one was for amplitude increases with offset to be
03:35 hydrocarbons, you would be drilling dry and believe me a lot of that
03:41 been done over the years. Uh you, uh but if you correctly
03:47 the data, you'll understand that what looking for for gas and you want
03:51 flat a the response in this particular and for brian sand, the amplitude
03:57 would offset would be indicative of brides . The other thing we could see
04:03 a very small change in V. . V. S ratio could give
04:07 a big change in the amplitude versus . So the seismic can be very
04:12 here to the presence or absence of . Okay, so a variety of
04:22 of rob rock physics in reservoir If we're trying to characterize the reservoir
04:30 we're trying to monitor the changes in reservoir and understand what they mean.
04:35 we watch the seismic data chan, rock physics is necessary for all of
04:41 . Uh, you know, for and we want to see the lateral
04:45 of rock properties brock physics helps us how the seismic data will change as
04:53 rock properties change direct hydrocarbon detection. just saw an example of that.
05:01 are conventional DHS or direct hydrocarbon There's a video analysis and pre stacking
05:09 and so forth. All of this calibrated with rock physics and you can
05:14 in the previous example that if you understand the rock physics generating the seismic
05:22 , you, you might uh, you're just looking at the seismic data
05:26 an attribute without understanding why the data doing what it's doing you're liable to
05:34 serious mistakes and then of course there the, all the engineering applications primarily
05:40 drilling engineering, but also in near geo hazards in uh, setting
05:49 uh, structures at the surface. , all of this involves understanding the
05:55 mechanics and the rock physics is helpful as well. What do I mean
06:04 reservoir geophysics by the way? I that course every other spring in our
06:10 graduate program? Uh, I define as the use of surface and
06:16 surface, seismic and borehole geophysical data to the extent that we can to
06:26 reservoir with ology porosity pore, fluid . And you can see that how
06:32 physics ties directly in there, lateral in continuity. Volumetrics, pressures
06:40 internal architecture of the reservoir. Rock is useful and directly interpreting the results
06:46 establishing frameworks for the results or at understanding the changes in the data by
06:53 way. Uh, this process could part of exploration where you have little
06:58 no well controlled or development where you potentially lots of well control and so
07:05 more well control you have, the you use the well log data itself
07:10 calibrate, the less need you have physics concepts, but certainly when we
07:18 have little or no well logs to , what's going on. The only
07:24 we have to hang our hat on rock physics. These quotes are from
07:33 , Wayne Pennington, who's an engineering at michigan Tech University. Um Well
07:42 geoscience says I'm not sure exactly come think of it, I'm not sure
07:46 what is dean of? He was was chair of the Geoscience department at
07:50 time and I knew Wayne when he , where I first knew Wayne when
07:56 was a assistant professor at University of . And I was a graduate student
08:02 I took an earthquake seismology class from , which by the way was found
08:06 difficult. But I went into the industry and then he did it.
08:11 did as well because they paid a better. Then he was getting us
08:16 assistant professor. Uh But then he went back to academia has had a
08:22 successful career and he's uh he's very got into reservoir characterization. So these
08:28 two quotes I took from him and one quote will the geophysical technique being
08:36 . Be able to differentiate between the reservoir models sufficiently well to be worth
08:42 effort and cost, you know, fellow I've been associated with the past
08:50 dr Marlon Downey. He was president a P. G. I knew
08:55 first when he came as president of oil company. I was working for
09:01 I attended many of his meetings and a tremendous amount watching him. But
09:08 , we both joined though, you the same time as professors at University
09:12 Oklahoma and he was right down the . So he went from the president
09:16 this giant oil company to this guy the hall. So I had the
09:21 to learn a lot from him. one of his famous quotes is geology
09:26 a business geophysics is a business oil gas operations. I'm sorry but no
09:33 totally wrong, geology is the science is the science. Oil and gas
09:40 is a business. I'm sorry, the correct quote. In other words
09:45 scientists, we always want more We always want exact solutions and so
09:52 . But the point is uh we know, time is money, there's
09:58 , there's money. How much is data worth? What is the cost
10:02 analysis of acquiring additional data? Scientifically want more. But just because the
10:09 , we want more data doesn't mean the company will be profitable for the
10:15 to acquire that data. So you to make decisions when you're going to
10:19 big money like acquiring time lapse, data or drilling wells or acquiring three
10:26 . Data whatever you're doing. It's talking millions and millions of dollars to
10:31 it. You have to justify it justify it. You need to have
10:36 expectation of what the result is going be. You have to do what
10:40 called a feasibility study and that. how do I determine? Okay I
10:46 spend $20 million for a time lapse over 10 years and monitor this
10:54 What good is that going to do ? What is it going to tell
10:59 ? Um You know I was working an exploration ist when three D.
11:07 started becoming popular and three D. very expensive at the time relatively.
11:14 And we'd have a discovery. So have a field we would want to
11:19 and we go to the management and say okay we want to spend $2
11:25 to acquire a three D. And management would ask the question,
11:31 many barrels of oil will that get ? And the wrong answer is well
11:37 I had the three D. I tell you I would be able to
11:40 you right. That doesn't cut You can't say spend millions of dollars
11:45 then I'll know what we have. right. That's not going to
11:49 You have to be able to you to be able to quantify what the
11:54 of acquiring that data is going to . How do you do it when
11:57 have minimal data to begin with? do you model, what's there?
12:02 do you model different situations and say the geology could be like this or
12:10 could be like that. The reservoir be here or it could be there
12:14 be connected. Maybe it's not You know could be losing reservoir quality
12:19 this direction or maybe not. How you know these things? Uh
12:24 you have acquired data to make those , but how do you know if
12:29 data is going to help you make distinction, you have to do what
12:33 called a feasibility study. So you to be able to say,
12:40 uh these are the possible outcomes. given the rock physics and seismic modeling
12:46 my knowledge of the seismic data I'll be able to differentiate between these
12:52 scenarios of what the reservoir looks So, um, the answer to
13:00 able to answer that question to do visibility study. You have to use
13:05 physics, rock physics of the reservoir and also rock physics of the layers
13:12 to the reservoir. And if everything working, you could do great
13:20 Like uh predicted the three dimensional distribution ferocity. This was a reservoir which
13:27 many, we could say flow units in many levels of high permeability,
13:35 are the sands. By the these are porosity, logs.
13:39 uh, the high porosity is to right. Low porosity is to the
13:44 . And you see, we've got zones that are particularly good thick and
13:49 porosity. We also have other zones that are impermeable. Their shells very
13:56 porosity. And then we have zones are of variable quality in between and
14:04 color behind it is very crudely predicted the seismic high porosity, which is
14:13 , low porosity, which is an intermediate porosity, which is
14:19 And so you could see um, know how things correlate here for the
14:26 part. You know when this layer example is showing up red at the
14:31 , it shows up red at the , it shows up right at the
14:35 and the logs. If I just at the logs, I would
14:38 well I have great flow continuity in . So, um, I
14:44 I should develop my field and place well such that I'll be able to
14:49 from here. For example, I'll able to drain everything down dip here
14:54 everything down dip here. Well, size makes tell me a different
14:58 The size makes telling me well this connected pretty well to that, but
15:04 connection to here is not that These sands may behave as separate
15:11 I may need a well in each these. Um, so,
15:16 apparently there seems to be a lot strata graphic complexity between these two
15:22 The well, logs alone. I tell you that. Maybe to get
15:26 stuff. Maybe I need a note well in there to get there.
15:31 , how do we get this seismic cube? It's a matter of calibrating
15:36 seismic data with the logs and understanding the seismic data will change as porosity
15:44 . So we see the changes in ferocity data. I mean the changes
15:48 the seismic data, we see, predict corresponding changes in the ferocity and
15:54 tie that back to the Prasit ease are known at the wells. We
16:03 uh to uh interpret seismic data in of directly seeing hydrocarbons. This is
16:11 case where we have amplitude variations related we think are related to hydrocarbons and
16:17 feel even more strongly about it because seems to be a flat spot
16:22 which is interpreted as a gas oil and a flat spot there. You
16:28 imagine there's a flat spot, there an oil water contact. In fact
16:35 with the color bar as it may more convincing as to what's going
16:40 But that's not enough. I these flat events, they could be
16:44 graphic, They could be multiples. , maybe you'd be more confident in
16:49 results if you could predict the amplitude and the magnitude the amplitudes of those
16:55 spots as I went from gas to and as I went from oil to
17:01 . If the change that I'm seeing the side work, the amplitudes I'm
17:05 at the seismic and how those amplitudes up dip in reservoir versus down to
17:12 that corresponds to what rock physics tells followed by seismic modeling, then I'm
17:19 confident that this is what I will . Here's an example from fred Hiltermann
17:31 there as well, that's a discovery is found hydrocarbons and in the
17:37 He's colored uh, brian field yellow, poor quality sands maybe thin
17:45 Shelly as blue shells is green and bearing sand has read these two and
17:55 looks like what we have is a configuration on top of salt. You
18:01 the lack of reflectivity in here. this is presumably salt and it looks
18:07 we're uh we've got traps on the of the salt down here which are
18:14 seismic responses indicative of hydro carpets. um, you know where I have
18:21 here in the log, I have here on the seismic and I go
18:24 dip and then I have read in trapping situation high on structure. Well
18:30 makes me feel good. That that's . Same thing here I have a
18:34 yellow in the log. I have on the seismic data. I go
18:38 dip. I have read could be and here I have hydrocarbons in the
18:44 and its threat. So um uh Is that difference is the way is
18:52 being read? The seismic being read that could that be caused by oil
18:57 example? And what's the probability that caused by oil? Uh is it
19:03 to be gas? Uh could be by little logic changes or there are
19:08 things that would produce that change in seismic response. Well, starting with
19:13 , well log we're pretty well constrained we could do some rock physics evaluations
19:19 that using equations. I could take brine out of this rock, put
19:25 in then do seismic modeling and see it gives me that response. So
19:31 certainly could give me more confidence in direct hydrocarbon indicators. This was an
19:42 I was pretty proud of around the around the turn of the the
19:49 Um my co office and I won paper in the leading edge for this
19:56 what it was was in the early of deep water prospecting. Um Well
20:05 border development, we didn't have a of experience drilling in these very unconsolidated
20:13 and but the practice at the time you have to have surface casing.
20:19 if you're going to develop a these were giant fields. Instead of
20:25 each well individually, they would draw wells from a platform on a
20:33 And what they would do is it be more efficient economically to put the
20:40 casing in for all the wells, finish that operation, then change the
20:46 , come back and drill the wells well individually down to the target.
20:53 the idea of the surface casing uh to um you know, maintain well
21:00 stability um in the where you have shallow plastic sediments. So this is
21:07 seismic data. And here where Pretty to the water bottom. This is
21:12 milliseconds here and the problem they suddenly at the Ursa field shall drill this
21:23 of surface casing and then they came to drill the other wells and they
21:28 that the surface casing had been buckled and sheared off. They lost
21:34 of the surf of the wells, shallow wells that had been drilled.
21:39 that was an economic disaster. And did it happen? Well again,
21:44 shallow sediments were very very plastic. could flow like a mudslide and they
21:53 in a very fragile uh meta stable , you could say, and disturbing
22:00 would cause them to fail. And essentially get a submarine landslide. And
22:08 so and and the zones that were susceptible to this was owns that had
22:15 high pore pressures. These were isolated pockets, shallow sands encased in shell
22:24 these sands developed very high pore pressures the sands to lose cohesion and flow
22:32 mud. So in our rock physics evaluating this stuff, we realized that
22:41 a brian field, sand would very pore pressure would have a much higher
22:47 . PBS ratio. Been a uh san that's normally pressured. So if
22:55 could find abnormal V. P. . S. Ratios in the seismic
23:00 , we could find these sands that prone to failure. And so we
23:05 this by simultaneously inverting p wave seismic and peter s. Seismic data acquired
23:14 ocean bottom seismometers and we came up a V. P. V.
23:21 . Attribute. Uh This plot is deviation from the normal the PBS
23:28 in other words, there's a compaction in the V. P.
23:32 S ratio. And so we're going be PBS as you bury, the
23:38 will tend to decrease At the very bottom. We had b.
23:43 v. s. ratios as high 10. And as you buried the
23:48 , the B. P. S ratio dropped as they became more
23:52 , more consolidated. And so here V. P. V. S
23:57 of about three would have been uh , an average V. P.
24:02 . S ratio. By the this was a well location here.
24:08 didn't use the well to do this . And what we plotted here is
24:13 deviation from the background V. V. S ratio. So blues
24:18 normally Lovie PBS ratios. Reds are high B. P. V.
24:24 ratios. Greens are normal B. ratios. These would be your
24:32 the blues are slightly brian field sands are slightly lower V. PBS and
24:38 shells. So these are your sands the reds are abnormally high V.
24:45 . V. S ratio. These the rocks with abnormally high pore
24:51 And so we predicted that at the location here, uh you have had
24:59 zone with abnormally high V. V. S ratios suggesting abnormally high
25:04 pressure and that is exactly where they what is called a shallow water flow
25:11 the well. So we're able to the occurrence of the shallow water
25:16 This was particularly bad because you can the formation is dipping there. So
25:23 you wind up with a very plastic on a slope. So of course
25:29 going to fail. So these are kinds of situations you want to
25:34 So maybe you drill around it, know Professor I have a question.
25:41 . Uh In my mind over pressure have a lower VP velocity. Uh
25:50 they have lower VP as they lose . Is like that critical porosity
25:55 right? You lose cohesion, you low VP. Right? So as
26:00 increase the poor pressure, you're pushing grains apart and lowest Vp. Yeah
26:07 what happens is it lowers V. more and so the V.
26:13 V. S ratio goes up. now the other point in my mind
26:19 that the V. S. Should insensitive to the poor fluid. I
26:24 to the whatever it's it's it's sensitive the module lists of the poor fluid
26:33 it's not insensitive to the poor Think about it. If I increase
26:38 fluid pressure enough I'm going to force grains apart as I push the grains
26:44 , the rock becomes less rigid. , yep. So I pushed I
26:52 it, you know it's the grains providing the Virginia is the contacts between
26:57 grains that's providing the rigidity. And that poor pressure is high enough that
27:03 the grains apart and you lose your . That causes the railway velocity to
27:09 down. Yeah and the V. . B. S ratio to go
27:14 . Got it. Thank you. okay. Well hopefully that's enough motivation
27:25 the fact that you need the glass class to graduate. Right? But
27:30 could do important things with rock And if you're if you wind up
27:35 an exploration ist in the petroleum industry will be using rock physics. So
27:44 it behooves you to to use it . Right? So anyway learn everything
27:49 can in this class. It will will help you in your career.
27:54 so now we're starting now that you're motivated now we'll just start with the
28:01 and I'm going to cover a few topics first because you know geology in
28:10 mind is the driver for everything If we if we if we didn't
28:17 geology we wouldn't be geophysicists right? be physicists. And geophysics is a
28:24 discipline from physics for a reason because the integration of geology and physics.
28:31 a little bit of geological knowledge goes very long way. And uh you
28:37 there are only so many equations in we could use and things are so
28:44 non unique and under determined that we all the geological constraint we can
28:50 And so if we uh if we at our problems from a geological point
28:56 view it will lead us to answers a physicist could never arrive at without
29:01 geological background. So I'm going to some geology up front. And so
29:08 is a very basic geological question. is the most common mineral in the
29:17 ? Chief mineral uh have one vote courts any other. Do you agree
29:28 that? His courts the most common ? Um I was going to say
29:36 , but I guess it's mineral. not sure this applicable. Well,
29:40 is a mineral, Clay is a . Um So let me give you
29:45 perspective, you guys are already coming this from a kind of a petroleum
29:51 because what I asked was the most mineral in the crust. Remember the
29:56 section is just a very thin All right. You've got a lot
30:02 metamorphic and igneous rocks underneath. So factoring that and think of a
30:10 . Right, So, uh, think of of assault. So now
30:16 going to ask the question again, is the most common mineral in the
30:22 ? Yeah. Depending oceanic plates or of fate could be uh, person
30:29 the granite. Those are rocks I'm for mineral for from show me across
30:38 themselves. Then we've been oceans and uh, cloud your place. The
30:48 , purity scenes add color and pyrrhic scenes, they had color,
30:55 project places a dominant component what color most granite? Think about a granite
31:02 where Yeah, actually pink. That's , That's potassium feldspar. So,
31:13 of course is not the most common in the crust feldspar is.
31:18 now I'm going to ask the what is the most common mineral in
31:24 rocks? And the answer is Right. So what happened?
31:32 sedimentary rocks come from igneous rocks Right. Igneous rocks are primarily
31:42 sentimentally rocks are primarily courts. What ? Russian patient position instead of
31:56 I'm going to say weathering. And so when you weather, what
32:01 ? You convert felt far too So courts play Are two of the
32:12 most common minerals and sedimentary rocks. is the third most common matter?
32:23 ? Yeah. Thinking about carbon and calcite. So those are the three
32:28 . So those are going to be important minerals for us in rock
32:33 Right. So we're going to be to a large extent on those
32:39 So why is felt far? you know, you find feldspar in
32:48 rocks, even some uh sand stones primarily fills for like very immature sand
32:55 . Arcos, is they the grains traveled far enough to weather very
33:00 Right. Um but the main differences fell far disintegrates at surface conditions fairly
33:11 . And uh this is an interesting to look at that. This is
33:16 . These are calculations based on chemical um, Assuming uh water rock interactions
33:25 water over p five And temperature 25°C is pretty, pretty good surface
33:33 Right. And look at and what half life is? It's like radioactive
33:40 life? It's the number of years would take to reduce the volume by
33:46 . Right? So for courts, uh putting it in water under these
33:58 , Half of it would remain after million years. But look at an
34:04 which is uh feldspar. It's a of the plastic clays felt scores.
34:13 I think it's the calcium one. will last only 100 in 100
34:18 Half of it is gone. But you can see the other pills
34:23 us al bite um Maybe that sodium potassium feldspar uh they're almost an order
34:32 magnitude. Well, almost 1000 times faster decay than uh than courts.
34:42 , um that's the reason courts persist than the other rocks. And even
34:52 . Sometimes shells could be primarily Okay. Some more geological terms
35:06 Cleavage, Foley, ation layering, . You can see all of these
35:17 provide a essentially, maybe not layering are addressing a text. Kind of
35:24 layered banded type of texture, let's fine layering here. Thin layers,
35:31 on the order of centimeters where examinations be on the order of millimeters.
35:39 ? All of these factors will contribute anti Satrapi as we discussed.
35:46 let's uh let's make sure we understand each of these terms means. What
35:53 facility, anybody facility by the do you know the definition of a
36:13 ? What's the definition of a Organic? Pretty sure I would leave
36:23 organic at a shell can have high content. But it doesn't have to
36:28 a fine grained sedimentary rock. Plastic rock as opposed to a fine grained
36:36 . But it's more than just fine . If it's just a fine grained
36:43 , that's what the technical definition would a mud rock. It was very
36:48 grained. It would be a clay . If it was coarse grained it
36:51 be a silk stone. These are rocks. But what makes something a
36:57 ? Actually the definition is a fissile rock. So what we what is
37:05 . It's a tendency to part along planes. So a true shell,
37:13 though in the industry we tend to all fine grain facilitate plastic rocks,
37:19 though we tend to call them all . For example, the Monterey shell
37:23 California is a porcelain night. It's a shell. Uh But okay,
37:30 tend to call these shells a true shell is a parts along bedding
37:38 So that's what we mean by And that's a different concept in cleavage
37:44 is also partying. But we have cleavage and slate. Like cleavage
37:51 Uh So what are these? What mineral cleavage? I will say the
38:04 for murder. Yeah. And this really great tendency to break along planes
38:14 weakness in the crystal lattice. So that's mineral cleavage. And the
38:19 example of that is muscovite, It looks like a book, pages
38:23 a book. That's mineral cleavage. is slate like cleavage? Maybe you
38:33 are too young to remember blackboards now have white boards in my day,
38:38 had blackboards and we use chalk on blackboard slate is a metamor foes mud
38:44 , probably a shell metamorphose it's lost de positional betting and it develops fractures
38:56 very particular orientations with respect to the stresses. So that's the slate light
39:07 . What is Foley ation parallel arrangement certain minerals strains. That gives the
39:16 straight appearance. This is purely Uh That's a great, that was
39:24 if you had lived at that was , you nailed that. So uh
39:32 a strong affiliation, you might have shift, I don't know. Uh
39:40 anyway, assist you could actually, almost looks like facility, but it's
39:46 a metamorphic texture or in nice is get this banding. So uh but
39:54 ation tends to be less extreme then or facility. Especially in Nice.
40:02 the mineral banding that you get in . Is it tends to be gradation
40:07 and not a huge contrast in rock associated with the change of affiliation.
40:15 layering. We all know what that , right, you have different layers
40:21 different mythologies. And then nominations are , very fine grain layers. So
40:29 the order of millimeters. Now by way uh here is where geophysicists use
40:37 bad terminology when a a geophysicists call thin bedded uh huh. When a
40:48 says I have a thin bed, means I have a layer below seismic
40:54 . That means Below something on the of 50 ft. So to a
41:01 , 50 ft is a thin When a geologist refers to thin
41:06 he means less than a well logging resolution. So he means on the
41:12 of uh you know an inch or . Right, you're logging tool may
41:18 resolution of a foot or two. it didn't bedded zone would have many
41:24 layers on the order order of magnitude an inch. Um So geologists and
41:34 have a mismatch in terminology here. do be careful when you're crossing disciplines
41:42 misunderstanding can occur. Um Okay. then lamination is very very fine
41:51 Um Now what will all of these to geophysical properties in the case of
42:00 cleavage? If your minerals are aligned in a shell you have played
42:06 These are similar to muscovite clays are similar to Mika's um They're all what
42:12 call philo silicates there, they have like crystal lattices. Um So in
42:23 shell under pressure. Um Those clay tend to align. So the mineral
42:33 inherited in the grain shape which then producers. Yeah affects the seismic properties
42:44 of that alignment of the grains. , all of these of course will
42:48 the anti Satrapi. And they tend produce what we call and trans versus
42:56 or sometimes called transverse. Anti Satrapi a particular type of anti Satrapi,
43:03 is very common uh in our Okay, so I think we've already
43:14 ferocity but let's go ahead and do again. What is porosity for your
43:22 ? Because please void fraction. So it's the void volume divided by
43:30 total volume. And now that could expressed as a percent. So,
43:38 could say the porosity is 25% and I'm using percent, those are also
43:45 ferocity units. So 25 ferocity units 25%,, Which is .25 fraction.
43:55 so you'll see porosity expressed both It's usually obvious to know If you
44:03 to divide by 100 or not in rock physics equations, we will almost
44:09 use fractional porosity as opposed to present . Okay, so is there a
44:16 relationship between ferocity and geophysical properties? ferocity and velocity? Is that relationship
44:32 ? No, If it were I could tell you that I have
44:37 is 25% porosity. And so the must be, but 15,000 ft per
44:48 . Say uh but no, I say that if it's 25% ferocity,
44:54 could be anywhere, you know, a wide range, that's why we
44:59 the Royce bounce. Right? So is not a unique relationship between if
45:08 a unique relationship the Royce and avoid would be identical. All right.
45:14 what causes this spread at a particular ? This spread? Well, your
45:20 in composition, variations in fluid You have variations in texture, poor
45:30 , right. All these things cause degree of cement ation, degree of
45:37 . All these things caused you to a spread of values between the Royce
45:42 the voice mails just as we But on the other hand, we
45:48 have the widely widely equation. I , I can I can argue that
45:51 is a relation between velocity and Yes, that's the point. It's
45:58 relationship, but it's not a unique . It's a line between the Royce
46:04 boy bounds, which will work for a very specific circumstance and will not
46:12 in many other circumstances, but it's for us to realize. Yeah,
46:19 one of the important lessons in this . Okay, now, what if
46:26 kept composition constant? What if I environmental conditions constant? What if I
46:33 the poor fluid constant? What if only variable change changing is that fractional
46:43 of porosity? But I'm not saying saying anything about the way the ferocity
46:48 distributed. I'm not saying anything about shape of the ferocity. I'm just
46:54 everything else other than related to porosity constant. Do I now have a
47:00 relationship between porosity and velocity. I was hoping you'd say that because
47:13 answer is no. Yeah, I this is a trick question answer is
47:23 No. Because as the poor shape the type of ferocity changes, the
47:30 between velocity and ferocity changes. and that's another very important lesson from
47:37 course. So, if you want know the kinds of things that you
47:41 , I find important that will help determine the kinds of questions I'm going
47:47 ask on tests and so forth. . So, understanding how the shape
47:52 the forest affects velocity is very So therefore, now, you know
48:00 answer to the next question Does all affects seismic velocities in the same
48:08 No. Right. I think I you that answer. So,
48:18 let me let me ask you a question. Does all porosity affect density
48:24 the same way? No. Okay. For density, it doesn't
48:36 how the ferocity is distributed, it matter how it shapes, it doesn't
48:41 where it is in the Raqqa, long as it's there, it affects
48:45 density in exactly the same way. , so a fundamental difference between the
48:53 porosity affects density and the way ferocity velocity? If I tell you I
49:01 a pure limestone, it's all native , 2.71 g per cc is the
49:07 density for calcite. If I tell , I tell you the ferocity,
49:12 can tell me exactly what the density going to be using the mass balance
49:20 On the other hand, if I you I'm in calcite, it has
49:25 p wave velocity of six, km/s And I have a ferocity of
49:36 . I can't tell you what the is because just having the ferocity is
49:42 enough. I could have very flat crystalline ferocity. Micro porosity, that's
49:51 , that's very compressible. Or I have round historical buggy ferocity which is
49:57 to compress. Both types of ferocity density exactly the same way and they
50:05 a very different effect on the Okay, so what needs to be
50:11 to have a unique relationship between ferocity velocity is a constant poor shape.
50:20 if I tell you I have calcite And I've embedded 10% porosity. And
50:31 . The ferocity is all in what call a lip sides and these are
50:37 distributed ellipse sides with a aspect ratio a certain degree of flattening to these
50:46 sides. If I tell you the of planning of these ellipse sides,
50:52 all I need to know is the porosity and I could predict a unique
50:58 but I need to know the poor and the problem is pores are so
51:03 in shape and they're so irregularly It pours were all what we call
51:12 spheroid, for example that they were exactly the same shape. Uh then
51:20 physics would be easy. Okay, let's talk about the different types of
51:30 . We have lots of words to ferocity. What is connected porosity
51:43 Yeah, that's pretty obvious. But . In what way? When we
51:48 connected ferocity, we mean topological lee . That if you had a small
51:56 , if you were small enough in , if you could shrink yourself into
52:00 little submarine, you could find and could find a path from every,
52:08 one port to another. Those if you could find that path would
52:14 them to be connected porosity. And alternative to that is there is no
52:21 . And this would be disconnected So if I had an isolated spherical
52:29 , that would be disconnected if it intersect with any other force.
52:35 so the total ferocity is equal to connected plus the disconnected ferocity.
52:44 now, what is effective ferocity by way, in the petroleum industry,
53:01 is the most common ferocity that's What is effective ferocity? Um is
53:22 average frosty over a certain, over certain internet? No, that would
53:29 an average ferocity effective porosity. Is connected porosity such that the connections will
53:40 pore fluids to travel through them. over a time scale, uh,
53:50 a human time scale, right? a time scale of the production of
53:54 field. So effective porosity, has we call movable fluids in them.
54:03 could travel from one port to another another out to the well bore and
54:08 to the surface and could be So effective ferocity is ferocity that contains
54:15 that can be produced to be The porosity has to be connected,
54:23 not all connected porosity is effective. is that grow some other foods going
54:33 them like naked way? Thank you usual, special measures. And why
54:43 ? Why can't the fluids not flow them? Well, for a given
54:50 something is connected, whether something is or not, that term applies to
54:55 particular fluid, you could say. example, it could be connected.
55:01 could be effective for gas but not for a viscous oil. For
55:07 it has to do with the ability fluids to flow through and it has
55:12 do with the connections between the poor how small they are. If I
55:17 a very narrow corridor connecting one port another, gas or water may be
55:24 to flow through. Especially gas. is the most mobile water may be
55:29 to flow through. Light oil may able to flow through, but it
55:33 be a heavier oil can't flow through and it has to do with surface
55:39 has to do with capillary pressure. ? But the narrower a tube is
55:44 harder it is to flow fluids through . Okay, so you could have
55:52 that is topological lee connected. But poor thing, What we call the
55:56 throats, The connections between the maybe so small that hydrocarbons have a
56:05 time flowing through. Okay, so effective ferocity. Now be careful.
56:12 is not the same thing as total . And if you use, you
56:19 , engineers will frequently calculate effective And the way that's done is the
56:27 log analysis that is performed first calculates ferocity and then it reduces the total
56:35 often based on the amount of clay the rock to what is considered an
56:42 ferocity. But don't use effective ferocity geophysical calculations. All right. The
56:51 , for example, density seas, porosity, seismic waves respond to all
57:00 the ferocity, whether it's connected or . So for geophysical applications, be
57:09 in what you mean by in your of effective porosity, that maybe the
57:14 we want to predict. But don't the mistake of using effective ferocity in
57:22 or in understanding your seismic wave Okay, so what's trapped ferocity trap
57:36 is essentially total porosity minus the effective . It's that ferocity. The fluids
57:44 get out of that track ferocity might disconnected or it might be connected with
57:51 portraits. So, um, for reason or another, the fluids can't
57:57 out what is buggy porosity, frosty, uh, inbox and caves
58:09 land stones, dissolution. Yes. all of the above. Right.
58:16 these tend to be, uh, they're angular shape, but they're relatively
58:23 pores and they're more they're relatively Not smoothly, necessarily smoothly round,
58:34 they're not flat. Let's put it way. Okay, so and the
58:41 ferocity because these pores are large, a lot of the storage in a
58:48 , I'm sorry, not particular buggy because these pores are large, they
58:53 have high porosity but they have to connected to be productive. Right?
59:01 you need some kind of other type ferocity in addition to the bugging ferocity
59:07 join the bugs up to the point you can effectively flow oil through
59:16 So buggy porosity can often be So buggy ferocity provides good volume but
59:24 necessarily provide good permeability. Okay, ferocity is similar to bugging ferocity,
59:31 typically ferocity caused by bubbles. For , you find them in lava
59:38 So vesicular pores are typically very smooth very round. Okay, dissolution
59:47 you mentioned it before. What is solution porosity? It's caused by
59:58 dissolving grains or dissolving shell fragments or . Melodic ferocity is a type of
60:09 ferocity, but it's when you have complete shell that you are a large
60:16 portion of a shell that you could . It's from a shell fragment.
60:21 that would be moulded ferocity inter granular is porosity between grains. Similarly,
60:31 granuloma is porosity within grains. How that happen? Well, sometimes when
60:38 have small uh huh Or forums or or things like that? Sometimes you
60:46 ferocity that remains inside these things um crystalline porosity. This porosity between crystals
60:59 very often sedimentary rocks have re crystallized limestone and Dolomites and sometimes you get
61:08 between the crystals. You can also ferocity within the crystals. For
61:14 fracture porosity is probably caused by fracturing rock and you could have micro fractures
61:22 can be um within crystals. Micro generally refers to very fine grain poor
61:34 associated with plays. So between clays as opposed to um uh huh micro
61:49 themselves. So micro porosity any very four, what is bound water?
62:03 usually around the shale minerals. Its , it's the water connected to the
62:10 the shale grains to the green. ? So bound water is water associated
62:17 plays uh it could be trapped in porosity or it could in fact be
62:25 within the crystal lattice of what we swelling clays. Okay, primary porosity
62:32 ferocity inherited from the time of Secondary porosity is porosity that was produced
62:40 dia genesis. So for example dissolution would be a type of secondary
62:48 If the inter crystalline ferocity is due re crystallization, that would also be
62:53 type of secondary porosity fracture porosity and porosity is often called secondary porosity now
63:05 have different kinds of ferocity. Any on how these different types of ferocity
63:14 seismic velocities for example remember they all density in exactly the same way.
63:20 doesn't matter which of these they are long as they are boy space filled
63:26 fluids, then they affect the density the same way. Um So let's
63:35 through this list and think about the on geophysical properties um connected without seismic
63:43 . Don't care if the pores are or not. Typically at higher
63:48 That may be an important may be . Total porosity. Yes, the
63:53 waves see them of course, it different ferocity to different different degrees,
64:00 ferocity. Again, the seismic waves care if the pores are connected or
64:07 effective porosity. Well, the seismic again, don't care if petroleum fluids
64:15 pass through the rock or not. track porosity, similar arguments, buggy
64:24 and particular ferocity also often usually dissolution . These tend to be pretty
64:33 Uh huh. When we talk about shape of Iraq, we talk about
64:38 aspect ratio, that's the ratio of minor access to the major axis.
64:45 of these tend to have high aspect , buggy the secular dissolution ferocity and
64:52 they have high aspect ratios, they strong pores. Um it's hard to
65:00 around poor. It's much easier to flat course, which brings us to
65:06 ferocity, Mobic porosity can be round example, it's a small round shell
65:15 dissolved or it could be flat if a shell fragment. So multiple atrocity
65:22 can go either way in terms of it affects seismic ways inter granular
65:30 Well this encompasses different kinds of pore . There are the pore spaces between
65:44 which tend to be relatively large void but there are also the void spaces
65:50 the vicinity of grain contacts which tend be relatively flat Uh effectively into granular
65:59 acts like it has an aspect ratio the order of .1. So it's
66:05 compressible than round forests, which are closer to one in an aspect
66:11 An inter granular ferocity tends to act not quite as compressible as fracture
66:21 but somewhere in between fracture porosity are lowest aspect ratios, fractures are long
66:31 flat and are very compressible. Macro may be few and far between,
66:39 microfractures may be distributed throughout the rock therefore may have a more significant effect
66:47 the velocity bound water is connected to volume. And often in our
66:56 we will incorporate the bound water properties the shell property. So if I
67:04 and a light grain and I like has pretty similar mechanical properties to
67:12 which is relatively in compressible but typically our calculations we treat clays like they're
67:21 compressible. We treat the claim mineral like it's very compressible and that's because
67:28 incorporate the bound water with the mineral . Okay, by the way,
67:38 were definitions there in there. In notes. Okay, so here we
67:49 thin sections of a number of different rocks. And uh the thin
67:57 the ferocity is embedded with blue So the blue here is not
68:06 it's the epoxy, but that's the . And you can see we have
68:11 variety of different uh poor shapes. pores are very irregular. In some
68:18 , in other cases you can almost them like number F. You could
68:23 these pores as a lip sides. Sometimes their their roundish smooth with smooth
68:31 . Sometimes they have very sharp Um What about which of these uh
68:39 have the highest permeability, would you ? Mhm. Age. Yeah,
68:51 again, you know, with the , there is tough, you
68:56 maybe those connections are too small to flow through effectively. But assuming that
69:05 , you do have an interconnected poor here, so assuming the poor throat
69:11 wide enough that the oil can actually through and that would be a good
69:18 . You see an F. We a situation or G. Is
69:21 That's an example where we have beautiful pores, uh but it's hard to
69:30 connections between those ports. Right? um you know, F and
69:36 There's a lot of storage capacity in big pores, but those big pores
69:44 to be connected in order for that , what's stored in those forests to
69:50 produced. Okay, so some ferocity express total porosity as the sum of
70:02 other ferocity ease In two different Well, I'll make it easy.
70:10 porosity equals connected plus disconnected porosity in primary plus secondary porosity is equal to
70:18 . Plus trap ferocity uh Which poor be more compressible. A flat poor
70:25 a spherical poor of the same volume . Yes. And please don't come
70:34 of this class without knowing this. is very important. We'll come back
70:39 this again and again and again to to understand velocity dependence on ferocity.
70:47 flat pores are easy to compress. pores are hard to compress. This
70:54 why we use arches in architecture. fact the name architecture, the word
70:59 comes from the term arch. Why we use arches in architecture? Because
71:06 are strong and arches are hard to . Which ferocity then will affect velocity
71:17 per unit volume of ferocity fracture porosity buggy ferocity reflection. Yes. So
71:32 could have a low fracture porosity that me the same velocity as a high
71:39 velocity, High buggy ferocity. what is clay? Mm Who is
71:57 funerals? There are such things as minerals? Yes. Is that the
72:04 way I choosed? Yes, So there are two meanings for
72:15 Clay is A particle less than .002 . That's pretty small. Um and
72:27 size fraction is often dominated by clay . Clay minerals are primarily small.
72:36 break very easily because there are sheets so they're not very very strong and
72:42 could easily break. So um the size fraction is often but not always
72:51 by clay minerals. You can get lot of very fine grained courts to
72:55 fact sometimes you have shells that the mineral is courts in the shell.
73:06 . Some more terms that we're going use. We might as well define
73:11 . What is gas? We've been about gas. Does anybody know what
73:34 is? Oh also it goes the myself. Uh fruit freely woman particular
73:48 motion of we need to make a rapid motion. Good. That's a
73:59 . Um So gas is a fluid the particles move independently with no orderly
74:10 . So then how does that differ a liquid? What is how is
74:14 liquid different from the gas in The topic? Als competitive emotion and
74:25 if possible. Okay, so the move more slowly. Um They're also
74:37 together and they do have some orderly . For example, there's surface
74:46 there's laminar flow and things like So there is some order to the
74:52 of molecules. And so both of are fluids. What does uh So
74:59 does that mean? Why are they ? Well, the both glucose,
75:07 almost there will fix shit. Well that's that's you got it.
75:18 They have no resistance to change change shape. They have zero rigidity as
75:23 consequence. They flow now by the , a liquids are often described
75:33 engineered by engineers as being in The fluids are in compressible in that
75:43 , that doesn't mean that they have low, have a high bulb
75:49 Is right when, when people say fluid is in compressible, that means
75:55 they're unconfined, you can't compress they'll squirt away, will flow
76:02 However, if you could contain the then you could compress it very
76:09 So, in a poor fluids are compressible. Um If there is no
76:15 for them to squirt out of the um Now in a porous permeable
76:23 you might think that the pores are to the fluids are free to squirt
76:28 of the rock. But remember other are being compressed as well.
76:34 So in essential, there's no place the fluids to go. There being
76:40 . Uh nearby pores are being Now, sometimes, if you have
76:45 is a different shape as you compress rock. Some pores will open up
76:51 some pores will close. Also, parts of the wave front you have
76:57 the waves propagating parts of the rock the stretch. Parts of the rocks
77:01 the squeeze and fluids then will flow one part of the rock to another
77:07 of Iraq. Um but if they combined, confined, if they were
77:14 a disconnected poor or a trap they would have no choice but to
77:22 the compression. Okay then what's next on the spectrum is a solid,
77:30 is the solid? Where molecules, , we're molecules um are connected closer
77:42 closer together and it has a resistance this change of shape, yep,
77:48 it. Now the molecules will still but they won't move very be able
77:53 move very far. Okay, now the difference between a crystalline solid and
77:58 non crystalline solid? Yes, so solid, we have a crystal lattice
78:14 in a non crystalline solid, there not an orderly arrangement and and so
78:22 as a glass. Okay. And already defined the term rock.
78:34 Mhm. Well, maybe I shouldn't asking you guys, but I'll ask
78:39 since he's objective. What time is class supposed to end? Oh
78:48 Okay, so we've got a few minutes that gives us time to discuss
78:56 scales of measurement encountered in rock And so 1st I want to define
79:09 terms like homo genius, homo genius the property is the same, every
79:19 . So no matter where in the , I measure its ferocity is the
79:23 or I measure its velocity. It's same. Every place the same.
79:30 means the property varies as a function position. However, whether you're homogeneous
79:38 heterogeneous, depends on the scale of . For example, consider what we
79:44 consider homogeneous sandstone or its ferocity is same. Yeah, and its velocity
79:51 the same, no matter where I within this formation, it's all the
79:58 . Well, if I were able make the measurement at a very fine
80:03 , if I were to go into four space and measure the velocity,
80:06 would measure the velocity of fluid. if I went into a grain I
80:10 measure the velocity of the grain. if I had a mixture of different
80:14 grains, different grains would have different . So on a microscopic scale it's
80:21 but macroscopic li it's homo genius. we will often, when we stay
80:30 a genius, we often mean homo at the scale of the measurement,
80:36 though it may be heading Virginia's at finer scale. And then we already
80:43 about an ice octopi. So that the property varies with direction. Um
80:52 . So if I'm at a point I'm measuring ferocity, it doesn't matter
81:00 direction I measure the prostate front. could I could be in a thin
81:04 . I could point count from the to the right or the rights of
81:07 left. I still get the same right. So and so porosity is
81:15 anti psychotropic but we've already seen that is if I'm going across the foley
81:23 , I have a slower velocity and if I'm parallel to the layering of
81:27 fall foliage nation or the dominant a fracture set etcetera. So what
81:37 permeability. Its permeability. Ic tropic anisotropy turns out current ability is usually
81:51 psychotropic. The vertical permeability is usually lot lower than the horizontal permeability.
82:04 , so different scales of measurement. we're gonna so we're going to collect
82:12 at all these different scales and we're to try to relate the measurements at
82:18 scale to the measurement and another So I can make measurements on core
82:24 . So that's the plug is on order of an inch or so.
82:30 core measurements often flow properties are measured whole core. We have some velocity
82:38 on Hulk or these are usually on order of a couple of feet foot
82:42 ft. Well logs the resolution of logs Um tends to be on the
82:50 of two ft. We have some resolution logs maybe resolution. Well for
82:56 a formation micro scanner can see So it's measuring resistive itty at a
83:03 fine scale. Um And you have sonic logs that have resident or or
83:10 itty logs that maybe on the order 10 ft resolution. Most sonic logs
83:15 a resolution of about two ft density about a foot and a half.
83:23 we have borehole geophysics resolution on the of tens of feet. And then
83:28 have surface Seismic data resolution on the of 50 ft, 100 ft.
83:37 different measurements at different resolution by the . What is, what is heterogeneous
83:42 one scale may be seen as homogeneous another scale. Now, think about
83:55 these are all acoustic measurements, think about the wavelengths. Think about
84:00 volume of rock that is being So in corporate plugged, you have
84:06 short wavelengths. Uh wavelengths, fractions an inch. Surface seismic data,
84:15 know, on the order of 50 ft say could be worse. Could
84:21 better. Could be worse. Um we expect those measurements to be the
84:31 ? Um Well, first of there's a sampling difference, right?
84:36 sampling a very small piece of rock sampling very large piece of rock.
84:46 the properties are average differently. Um is dispersion. So there are sampling
84:58 , there's also the frequency dependence of velocity. To make measurements on core
85:04 plugs, we need ultrasonic frequencies. have to be at frequencies such that
85:09 geometry of the experiment doesn't affect the anymore. So our wavelengths have to
85:15 a lot shorter than the sample Otherwise, the sample geometry then affects
85:21 measurement. We don't want that. in a porous rock, you must
85:35 dispersion in a well, since we're not going to cover attenuation, I'll
85:44 a few words about it. if I make measurements on the
85:50 geophysical, if I propagate seismic waves the moon, my attenuation is very
85:59 . I make the same type of in the same time type of material
86:04 the surface of the earth and I have very high attenuation. The difference
86:09 the moon is completely dry and the is moist. The presence of water
86:16 the primary factor affecting attenuation in the . You may continue in continuation measurements
86:24 dry rocks. You have low You make the same measurement on a
86:31 saturated rock or partially saturated rock. you have very high insinuations. So
86:39 essentially to contributions to attenuation. There's the way, what is attenuation,
86:49 I'm talking about it. We haven't it. What is attenuation?
86:54 we want to between Yeah. The of what amplitude? Okay. Loss
87:03 amplitude as the way propagates. Why is it losing apathy? Like
87:11 said earlier on you to water? there's Okay, but you skip this
87:19 . That Okay. Yeah. I , I'll come back. You
87:23 I'll agree with you that water is big factor. But what is
87:28 you know, if we were losing , what else are we losing?
87:35 we're losing energy, aren't we? , energy is not created or
87:40 Right? So we're not. The is not going away. It's being
87:46 as the wave propagates. What's it converted from? And to So I've
87:57 I've always learned is transformed into heat uh liam Thompson lecture where we talked
88:05 fluid squirting. Uh The fluid squirting has to has to do a generation
88:14 heat. I'll come back to that a second. Okay, in elastic
88:21 . you know, as opposed to things like that. But actual absorption
88:29 when we're converting from mechanical energy to energy as the way it propagates.
88:36 why do we generate heat? Why the waves propagating? Why are we
88:43 heat? And it transforms into kinetic energy of the fluids? Uh
89:00 I mean it's just the friction. guess that the fraction you got it
89:05 your hands together, they get Okay, So it's what we call
89:11 friction as the way propagates through the . Were deforming the rock and things
89:20 rubbing against each other, Right? what's causing the attenuation now. So
89:26 things could be rubbing against each grains could be rubbing against grains.
89:32 call that solid solid friction. But more important, his fluids rubbing against
89:41 , flu is rubbing against solids, fluid, solid friction. Now,
89:47 I squirt fluids around the fluid that's going to cause a lot of
89:55 , isn't it? Yeah, So that's what uh there are 22 types
90:04 fluid flow in in Iraq as a it propagates through that is what we
90:11 slotting losses, slashing is inertial as wave is propagating through. The solid
90:20 is slightly out of phase with the , right? So I moved the
90:26 frame and the fluids move differently. like walking with a pail of
90:32 right? The pale has a certain . The fluids have a different
90:37 right? Um Those are sloshing losses in Iraq we have pores of different
90:46 . So if we're opening up one and squeeze in another, poor,
90:50 could squirt fluid from one pour into . So both those types of fluid
91:00 rub against the solid, generate heat cause attenuation and fundamental laws of
91:14 The Cramers. Krunic relations. If have frequency dependent attenuation, I have
91:25 by the way. Attenuation is measured the energy loss per cycle of
91:33 If I have a similar amount of loss for every cycle of propagation in
91:38 frequencies, I'm stretching and squeezing the very rapidly at low frequencies. I'm
91:45 it slower. And so I have cycles of deformation at high frequencies.
91:53 I have more generation of heat. the attenuation itself becomes frequency dependent and
92:03 necessary consequence of that. Is that are frequency dependent. So, if
92:09 have insinuation, I have dispersion. I make a measurement at seismic
92:15 I have less cycles of propagation than I make a measurement over the same
92:20 of rock and ultrasonic frequencies. So should expect my velocities to be
92:31 Okay, well, I don't want start a new topic. So,
92:34 there any questions then? All You'll make me very happy if tomorrow
92:43 you have questions, that means you've about things a little bit more.
92:47 puts me in a very good which makes everybody happy. I
92:52 So do try to start try to with questions in the morning.
92:59 so I will, I will, not sure when I will be able
93:05 get the downloaded um, uh, . You probably don't want to look
93:10 it tonight anyway, so probably sometime we'll get these on on blackboard and
93:19 you'll be able to spend your sunday to all this stuff again.
93:26 So that's it. And we'll see tomorrow at 8:30 professor. Quick
93:33 Uh, would you prefer me to in caucus tomorrow or or if it's
93:40 with you can continue attending all up the exam. I mean, I
93:45 no preference at all, but you have to be there face to face
93:50 the example. Sure. Okay. thank you very much. All
93:58
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