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GEOL7324-Rock Physics - ThursOct21
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00:01 this conference will now be recorded, conference will now be recorded.
00:11 so since fluids have no rigidity, we can assume their share module is
00:18 . So, the only two fluid that we need to worry about at
00:23 frequencies are the density and the bulk of the fluid. So, fluid
00:30 fluid bulk module lists as we move higher frequencies, the fluid mobility is
00:36 to become important, but we haven't to that yet. And so in
00:42 and the next unit, we're going assume we're operating in the low frequency
00:49 . And uh you'll see what that when we move on to more advanced
00:55 , when we start talking about Uh So, but right now,
01:00 going to focus on those two fluid . And the complication here is that
01:06 highly variable for the same fluid. You know, in the case of
01:14 , we could assume that the mineral , the bulk modules and density of
01:19 mineral was pretty much independent of the and pressure range that we're working in
01:26 rocks in the near surface or the few miles. Um So, we
01:33 have to worry about temperature. On other hand, the fluid well,
01:39 pressure either for the mineral properties. the other hand, both the fluid
01:44 and the fluid module lists are strongly on temperature and pressure. So they
01:49 be very depth dependent and they'll be locality dependent. And so we're going
01:56 have to think about the variation with and pressure. And that means we
02:02 to think about temperature a little So I'm going to digress a little
02:06 . These are some of the new I've added to this unit and talking
02:11 earth temperatures because we're going to have take those into consideration. Now.
02:20 , we'll find that or all oils not the same and there's a wide
02:27 in oil properties. Uh, you heavy oils that could be more dense
02:33 less compressible than water. And you have very light oil properties that could
02:41 a lot like gas and can produce spots and uh, HBO anomalies,
02:48 . So, we have to think what factors affect oil properties. And
02:53 are primarily the api gravity and the oil ratio. In fact, the
02:59 flow ratio is extremely important. I'll about that in a minute.
03:06 the api gravity is a measure of density of the oil. And you
03:13 have oils with very widely compositions. are complex mixtures of very, you
03:20 , a lot of long chain but also a bunch of other
03:25 All kinds of organic liquids and other . And so, uh, we
03:34 have systematics of oil properties versus their , but we could capture most of
03:42 in the oil density. So, of different compositions with the same oil
03:47 will have similar acoustic properties. So talk about a, the api gravity
03:54 little bit. And the gas ratio the next unit will then take these
04:00 properties and we'll put them into And for that, we're going to
04:05 gas lens equations at low frequencies. we go to higher frequencies, we
04:11 to use B. O. Gas means equations are the low frequency
04:17 of the video theory. The and thought it worthwhile to start if we're
04:28 to talk about temperature effects. I it's worthwhile to talk about the difference
04:34 hate heat and temperature because it's a a subtle difference when we think about
04:43 . We're really thinking about the transfer energy from one body to another.
04:49 we think about heat flow. It's movement of energy. Right? And
04:56 is measured measured in jewels. Uh what is the heat itself? And
05:03 done in the past few hours, done a lot of reading on different
05:10 of heat. And I finally came one that that please make conceptually
05:18 And uh here it says he is measure of how many atoms there are
05:24 a substance multiplied by how much energy atom possesses. And that energy is
05:32 kinetic kinetic. Remember the uh the or molecules are molecules are vibrating.
05:40 have kinetic energy but they also have energy. So he is a measure
05:46 the total energy. Now, what the kinetic energy? You remember one
05:51 and B squared? So it has do with the velocity that these particles
05:58 a given mass M are moving But the more particles you have,
06:03 more energy you have. So he a result of not only uh how
06:11 the particles are moving and their so what their kinetic energy is,
06:16 also how many of them there Whereas temperature is more like a potential
06:24 you know, like fluids move from pressure to low pressure, heat moves
06:29 uh high temperature to low temperature. , but what is the temperature?
06:38 it is related to how fast the are moving within a substance. So
06:44 higher the temperature, the the higher velocity of the atoms that means.
06:50 uh at higher temperature an atom of particular mass has more kinetic energy associated
06:57 it. But it's only the velocity , it's not how many of them
07:05 moving. Right? So temperature is a potential. It it tells you
07:13 direction that the heat is going to . So he can do work.
07:21 a transfer of energy, but temperature just a measure of the degree of
07:27 the potential of the heat. and by the way, I gave
07:33 the link to the site where I this, um I found a lot
07:38 the other discussions, I mean if look at the equations, those are
07:42 . But when you actually conceptually put into words, I found a lot
07:46 the other discussions pretty confusing. Now if we're going to talk about
07:55 variation in the earth, we have think about thermal conductivity, thermal conductivity
08:02 a rock property, like like a of the rock. Uh and it's
08:10 to the to the variation of temperature distance. So the temperature gradient,
08:22 if you look at the heat flow . So that's the the movement of
08:30 , uh how much heat is Uh that is equal to a constant
08:38 the temperature gradient. And the minus is here is because the heat will
08:44 from high temperature to low temperature. , if I have a high temperature
08:51 , uh that means, you in a given direction, that means
08:55 have high heat flow moving in the direction. That's the only reason for
09:00 minus side. Uh So the thermal is then the ratio of the heat
09:06 to the temperature gradient. Or you say the temperature gradient is equal to
09:12 the heat flow divided by the thermal . Yeah. Uh just the equation
09:22 simple, but I just want to the point that for a given temperature
09:29 , a good heat conductor has high flow. So, it would have
09:33 high thermal conductivity, right? You , this is constant, high heat
09:38 , high thermal conductivity or for a uh heat flow, high thermal conductivity
09:48 have a smaller temperature gradient. So a low thermal conductivity, material
09:57 have a high temperature gradient. And we look at it, see here
10:01 death, then uh a low thermal will have a high variation of temperature
10:08 death, by the way, thermal acts a lot like velocities to,
10:16 example, velocities. For example, I have a sphere pack, the
10:21 the coordination. If I have a fear pack, the heat will move
10:27 the solids. The solids have much thermal conductivity than air. Remember,
10:32 is an insulator, right? That's layers of clothes worked so well,
10:36 you have air in between. This why if you're a shipwrecked in the
10:41 Sea, if you're on a you'll live a lot longer than if
10:45 in the water. If you're in water, you'll die very quickly of
10:49 . Uh that's because water is a better conductor of heat than air
10:56 Right. So, a dry rock have low thermal conductivity. The same
11:01 filled with water will have higher federal . Gosh, that's a lot like
11:06 right now. Also, if you about a dry sphere pack, the
11:11 the coordination, the more grain to contacts, the higher your thermal conductivity
11:17 going to be. And one more courts. The mineral courts has a
11:23 thermal conductivity, then closed it. , uh there is a relationship then
11:34 the mythology and the thermal conductivity. and since velocity is uh similarly
11:45 we could find that in a given , there is a relationship between the
11:49 conductivity here on the vertical axis and p wave velocity. Similar factors are
11:57 both. So, if I have shell, I might have a trend
12:01 this. I mean, this is an empirical trend. 1 -3
12:07 This is why I like to use . That's not the velocity of
12:10 That's the volume of play. But , this is what was in this
12:15 . So, uh one minus the of play. Time's the P wave
12:21 . So, they're they're basically interpreting a shale line, a Sandline and
12:26 share line here. And they're finding data points are in the tweet.
12:32 , shells the more organic material, have to lower their thermal conductivity.
12:40 has a very low thermal conductivity. will act like a blanket.
12:45 And so organic shells will have low conductivity. So it's not just the
12:51 , it's also the organic material in shell has a big impact, which
12:59 us to the geothermal gradient. So we know as we get closer to
13:04 core of the earth temperatures go up . We're at the very narrow
13:09 But yes, temperatures are going up we moved down into the earth.
13:16 and so the rate at which the increases is the geothermal graded. So
13:22 we have a very near surface Uh we have sand at the
13:27 Uh We have shell and then we into igneous rocks granite here and what
13:33 seeing is that they this is You're seeing a smaller increase per unit
13:40 . A larger increase per unit Back to a smaller increase. And
13:45 is inversely proportional to the thermal The shells have low thermal conductivity,
13:52 and granite have higher water, saturated and granite have higher thermal conductivity.
14:00 so they have a lower geothermal Very often we ignore the little logic
14:06 will just assume a certain degrees per death, I assume, you
14:14 uh, approximate this with a straight . That's often the case. But
14:20 know, if you, especially if doing based modeling, you know,
14:25 modeling of hydrocarbons, etcetera, you want to take into account the mythologies
14:30 well. Now, the reason of onto these topics is, as I
14:40 , our fluid fluid properties are very on the temperatures. The solid grains
14:51 don't care very much what the temperature , but the fluids care a
14:55 So now we'll talk about the different and we'll start with gasses and the
15:03 we describe hydrocarbon gasses is by their gravity Again, instead of thinking about
15:10 mix of uh, you know, chain hydrocarbons that make up the
15:15 you know, how much methane, much methane, how much propane
15:19 etcetera. We'll talk about the gravity the gas. What is the gas
15:25 is the ratio of the gas which is mass per unit volume of
15:31 gas to the density of air at temperature and pressure. I should have
15:38 that. Alright, so, at surface, basically, uh, because
15:46 a ratio of densities than it has dimension. A light gaffe, it's
15:52 low specific gravity. Heavy gas has higher specific gravity. So,
16:00 here we're looking at the gas modules temperature. Uh, this was based
16:07 the work that Mike Castle did many ago. And so we have what
16:14 a like gas, uh, often the dry gas. So very short
16:20 short chains of hydra apartments. So , that means it's less dense than
16:28 . That means it will rise, ? Uh, and we have heavy
16:34 , that means it's got longer and chain hydrocarbons. And these can be
16:41 than air. Uh huh. But can see a strong dependence, especially
16:48 the heavy gas at high pressure. see a strong dependence on temperature.
16:54 the other hand, at low there is almost no dependence on
17:00 What, you know, at low , that the gas molecules are far
17:07 . In fact, there is no on the gas gravity. It doesn't
17:11 , you know, it's so the module is so low, it
17:14 matter whether it's a dense or light , the molecules are so far
17:19 If you raise the temperature, they're going to move faster. They're
17:23 you know, move around faster. they won't just because they're moving
17:30 There's still so far apart that the is still highly compressible. However,
17:36 we increase the pressure, we start those molly molecules closer and closer
17:44 So we increase the pressure and you know, the closer we push
17:51 molecules together, the less they're gonna it, they don't, you
17:56 you have a band of walls, you have, you know, the
18:00 molecules don't want to be pushed together they will repel each other. And
18:08 the closer you push them together, harder it is to push them even
18:13 together. So as you raise the , your module is goes up and
18:20 effect is bigger in a heavy gas in a light gas. So,
18:25 gas. Uh wow ! It's module is gonna get up into approaching the
18:31 range at high pressures by the way can relate these pressures. You
18:36 this is from the scientific publication, ? So they give it in bars
18:40 mega pascal's, You can relate one is 14 c. And remember when
18:46 were talking about pressure gradients, the confining pressure gradient is one P.
18:53 . I. Per foot. But typical pore pressure gradient is say 10.435
19:00 . S. I. Proffy. you can convert bars two ft and
19:07 do need to talk about that these we're talking about are going to be
19:11 poor pressures the pressures that the gas experiencing. So you can relate that
19:17 death using a poor pressure gradient um as we get to high
19:26 the pressure dependence decreases. Um and because the molecules want to vibrate so
19:36 uh that uh it doesn't matter uh pressure you're at, they're still moving
19:44 so much that they become very Oh and we and and these are
19:53 atomic decreases pretty much right until you to high temperatures where things level
19:59 But for the most part, you decreasing module lists with increasing temperature.
20:09 systematics for density as we increase the . The density goes down.
20:16 Because uh you increase the temperature of molecules bounce around more and they they
20:24 into each other and they scatter They move apart. So the higher
20:31 temperature, the further apart they are to be so you can push them
20:38 . I'm sorry, we're talking about here, the further apart they
20:41 So the lower their density. of course, as you increase the
20:46 , you're pushing them closer together. at a given temperature, the density
20:53 . And of course the longer chains going to be more dense than the
20:56 . The shorter chain hide department. the lighter specific gravity is going to
21:02 less dense than a heavy gas. , so let me reiterate about
21:12 Uh the fluid modules and density uh with increasing pore pressure. These plots
21:20 shown you are the poor pressure. Now all else being constant. If
21:27 inside Iraq, if we just increase pore pressure, we've lowered the differential
21:33 and presumably we've lowered the effective Uh therefore increasing the pore pressure has
21:41 effects. It's making the fluid module less compressible but it's decreasing the effective
21:51 . So the rock frame is becoming compressible. It's at lower effective
21:58 But the fluid module is is less compressible. So you have competing effects
22:05 one or the other may dominate. it's the rock frame becoming more
22:11 That dominates but not in every Also, there are competing density
22:17 right? The poor pressure increases, material becomes less sense. Uh
22:25 I'm sorry, becomes more dense. And the but the rock itself,
22:32 is a plastic rock may become less you may increase the ferocity. You
22:37 the pore pressure, you're pushing out the pores, You may open up
22:41 pores. So you have competing its effects and you have competing density
22:49 . And in any particular case, that could go in any particular
22:54 Usually, the result is uh as uh uh increase the pore pressure,
23:01 velocity decreases, that's that's the usual . But which factor as a which
23:10 winds in a particular case though, on the local conditions. The rock
23:14 the environmental parameters and the fluid you're with these figures are pretty much the
23:24 data is from the uh the original paper by uh that's one long ZW
23:33 was a graduate student, a summer at Arco in our group and he
23:40 on to become a top manager at and uh he's got three rock physics
23:46 , he was the most productive summer we ever had in our group.
23:51 and he's had a very distinguished Um So anyway, that's just for
23:57 purposes, they did add one more . 10 mega pascal's. This 50
24:02 pascal's, that's 500 bars. So we had 502 and 250 And
24:09 , I think that's what we were at, right, 500, and
24:14 . And so they just added one 10 mega pascal says it's 100 bars
24:23 . Uh But anyway, these are to each other, the gas
24:27 the gas module list, you can they're acting pretty much in a very
24:31 fashion and just a few points to made. The gas density is also
24:40 sensitive um and that tends to be mono atomic. Uh huh. The
24:51 modules becomes relatively insensitive at high Right. These trends tend to converge
25:00 they at very high temperatures. They become less sensitive to temperature.
25:07 typically we're not up this hot, is 300°C Usually we don't get much
25:14 200. Um for light gasses, density and the bulk modules are relatively
25:24 to temperature. Right, so here where uh the lighter gasses less sensitive
25:32 temperature than the heavy gas and also very low pressure. We have essentially
25:39 temperature sensitivity for either either case. question. Yeah, I know we
25:49 to read that paper but is on previous graph. Is that data all
25:55 ? How did they uh where did get these results from? Yeah,
26:00 made they made a lot of uh measurements on fluids of different uh types
26:10 they fit empirical trend. You they measured velocity, they measure density
26:14 out the module is so these are module. I they also did it
26:21 other way around. They also did statically. So in the paper they
26:26 the difference between a idiomatic ma july ice, a thermal mon july so
26:32 module, light or maintaining constant I saw thermal module light, they're
26:38 constant temperature as the uh and so I refer you to that paper to
26:46 into that distinction. Uh and what find is you don't get perfect agreement
26:52 you deal with if you use, remember I was at a meeting at
26:57 stanford rock Physics Consortium where Z W was presenting some of his results and
27:04 of the top researchers, very famous . I won't mention his name from
27:09 research, stood up and said, are you bothering doing all of these
27:14 measurements? You could just use the of state and calculate these modules from
27:22 and that that information is all there the literature. And I remember Amos
27:27 , who was uh Z. S professor at the time, very
27:31 rock physicist. I thought he was have a nervous breakdown. He was
27:35 was so mad, He started Uh it was a very interesting interaction
27:41 . Uh, and the moral of story is uh, this top researcher
27:46 Shell is absolutely wrong. You don't the same answer. They're close,
27:52 they're not the same. And the way to do it is the way
27:56 our purposes, the proper way to it is the way wang was doing
28:01 using the dynamic module I makes you Excuse me The Banks. Okay.
28:14 , I'm always happy to tell war . That's why I like questions.
28:19 . So moving on to oil Um, it's a little bit
28:24 You know, when we talk about got gravity, a low gas gravity
28:29 low density. High gas gravity is density for oil. It goes the
28:35 way around. And uh it's not related to the specific gravity of the
28:44 . By the way, specific gravity would be the ratio of the oil
28:50 to water density at standard temperature and . But the term we use is
28:58 api gravity. And where in the this came from, I don't know
29:03 I'm going to have to try to the uh the way this is the
29:10 of a rose. But it's given this equation. So it's inversely proportional
29:16 the specific gravity. And so it's you take the specific gravity converted to
29:23 api gravity using this equation. what that means is because this is
29:28 the denominator here, higher oil gravity's lighter. Right? Um So typically
29:39 we talk about crude oil, we're about between 50 15 and 45° but
29:45 a whole range and this kind of more or less, this is not
29:54 precise science here, but if we at the specific gravity at near surface
30:01 here, um we have uh bitumen that some of the organic material that
30:10 in semis in semi solid form in , bitumen being soluble uh whereas carriage
30:20 is not. We have heavy Now, heavy oil is one that
30:27 won't flow on its own. You need some kind of enhanced oil
30:32 like thermally O R. Jeff steam up, lower its viscosity.
30:38 and let it flow. So, oils are very viscous. Uh We
30:43 medium oils. Light oils and you above 50 degrees. Api you have
30:52 condensate is it exists in the formation gas. It has gas like
31:01 is actually a supercritical fluid, we'll about what that means but acting more
31:07 a gas and a liquid. acoustically, it it kind of has
31:12 properties in the formation, but as bring it to the surface, you're
31:17 the temperature pressure and it will exalt oil from that super critical fluid.
31:25 will separate into a lot of gas some oil. That oil is what
31:30 call gas condensate. And so a , wet gas um would be uh
31:40 valuable than a try gas because the is more valuable. So, if
31:45 could pull condensate out of the gas , it helps your economics a
31:51 Uh you have higher, you have lighter gasses and then you have a
31:56 natural great gas or compressed national natural . So, uh, these are
32:04 the gas is put into liquid form transportation purposes. All right. Just
32:15 back to to the oil properties versus and pressure. You see a similar
32:22 as we had with gas, except at low pressure. We have some
32:28 modules and I think an important reference is uh, water module lists or
32:37 slightly saline brine modules which would be this vicinity here at the surface.
32:45 , about 2.5 giga pascal's maybe a less depending how fresh it is.
32:51 for water at the surface. Uh . And so, the oil module
32:58 if it's a a very heavy even under low pressure could have the
33:06 module lists as as water or at pressures can have even higher module.
33:15 right tip. Usually, oil will a lower module list than water,
33:21 it could be very, very In fact, when we uh in
33:26 early days of thinking about the effects oil on acoustic properties. The general
33:31 of thumb was it was expected that should be very similar to water.
33:37 the acoustic property should not be very . And that was not taken into
33:42 the effects of temperature. I was about the properties at the surface.
33:48 . If you just take lubricating, oil from can and measure its
33:54 it's going to be not all that from water, but you heat it
33:58 and it becomes much more compressible. there's another big swinger also. These
34:04 what we call dead oils. They always get the solution. Gas in
34:09 oil would have Exalted. So, are dead oil properties. And as
34:17 see, adding dissolving gas will reduce macho I greatly and again, similar
34:26 for oil density. This seems to very linear with temperature. Uh But
34:32 , if water is up here at surface STP, you can see for
34:37 most part uh we're less dense than , irrespective of pressure. Of
34:46 The lighter oils have lower densities. typical rule of them. If you
34:51 to put one number out of the , you might say .8 something like
34:57 for uh for oil density. Mhm. This was a heavy oil
35:06 new oil and these are the way velocities were. The properties were
35:11 the velocity would be measured as a of temperature. The density would be
35:16 as a function of temperature. And that he would extract the bulk
35:21 Just roe V P squared would be bulk modules. And again at high
35:28 water is around here around 5000. at high pressures you've got these heavy
35:36 are faster than water. Thanks. , this is an interesting slide which
35:47 the idea of live oil. So talk about this a little bit.
35:53 First of all, well look at velocity of the oil versus pressure at
36:01 temperatures. So, uh here we this particular oil at 22 23
36:13 And it's 72 C. Right? this is and near surface temperatures,
36:19 is a somewhat deeper in the And you have a linear increase in
36:27 with pressure. So that seems pretty forward. By the way, they're
36:35 velocities from their equations are not exactly same. There is some specificity according
36:45 composition of different oils. The baseline wang equations are uh empirical fits to
36:54 wide variety of composition. So there some discrepancy, but it's pretty small
37:01 you really care about being more precise that. Uh you could worry about
37:06 . But remember these are dead oils that's not what we have in the
37:11 and the Earth, we have oils gas dissolved in them. We have
37:16 oils. And so, let's look those properties. And what we find
37:22 uh live oil velocities are much We dissolved gas in the oil.
37:30 the resulting module list is much smaller , you know, again, more
37:37 less linear with pressure. Um But at the comparison between the calculated and
37:48 observed velocities, but the live they're absolutely dead on. Right?
37:54 , what that's saying is the gas ratio is dominating over the composition.
38:01 , we don't have to worry about discrepancy too much because it really basically
38:07 away when we're dealing with live Now, if something another very interesting
38:13 is happening here. As we get low pressures, as we get to
38:18 pressures, the velocity increases again. , what I'm going to ask for
38:25 a hypothesis. I'm going to ask an explanation why when we get to
38:32 low pressure, think about it, have a live oil, there's gas
38:36 solution, which is reducing the modules where the dead oil would be
38:44 we lower the pressure enough and the the velocity starts increase what's happening
38:51 Yeah. Could the gas be escaping . Exactly. Right. That's exactly
38:59 . We've gone below the bubble point dissolved gasses now exalting leaving behind.
39:09 and a liquid with less dissolved So, it has a lower gas
39:15 ratio. If we exhaust all the that would bring us back to
39:20 Here we're eggs solving some of the . Now notice oil also, very
39:26 , they didn't make measurements at very pressures. They did on the dead
39:30 . No problem. But somehow experimentally got stopped at that point. They
39:36 keep going to lower and lower What do you think happened there?
39:45 did they stop making measurements? Maybe was a limitation of the instrument?
39:59 , yeah, it was an experimental , but why there's so much gas
40:07 that the live oils are like Pretty 50 oils at that point?
40:15 then they would have been able to the measurement. I think what happened
40:20 they started introducing bubbles enough gas, eggs solved that. Now, they
40:27 two phases instead of having a, know, uh in an oil and
40:34 a few bubbles, which aren't having big impact on the, on the
40:39 . And so they're able to measure oil properties below this pressure. So
40:45 bubbles have come out that they've started with the signal. Uh you put
40:51 in the fluid and it's hard, get a lot of scattering, it's
40:55 hard to transmit uh signals through As a matter of fact, that's
41:01 of the reasons that santa claus are unreliable in gas transfer for us.
41:06 you have a lot of gas in drilling mud escaping from the reservoir,
41:11 creates a tremendous amount of noise. makes it very hard to make the
41:17 . So a lot of scattering from bubbles here, They're unable to make
41:23 measurements anymore. So they start, , okay. So what is the
41:32 oil ratio in practice as a practical at the surface? Um They get
41:43 said they have a separator that separates liquid from the gas. So you
41:47 this mixture of gas and liquid and coming up to the surface also
41:54 but they separate, they have a that separates them. Now in
42:00 two, you may have may have a live oil with a certain gas
42:03 ratio, but as you bring it the surface, what are you doing
42:07 the pressure? You're reducing the And so it's the same way it
42:13 in the laboratory there, you get coming out of solution. So even
42:17 you had a liquid oil in the , by the time you brought it
42:22 the surface, you've got gas being , an oil water mixture being produced
42:29 you have to separate all of right? So you separate it and
42:34 look at how much gas, you one volume of gas, you
42:37 you fill the tank with it. you measure how much gas, you
42:41 how much oil and you measure at conditions. Um and that's the gasela
42:50 . And the presumption is that that the ratio of gas to oil in
42:56 in the reservoir and the liquid that in the reservoir. Now, at
43:01 surface there are two phases. It's we call free gas, it's not
43:05 gas anymore. But anyway, that how we measure the gas oil
43:11 it's a volume for volume. So could be gallons of gas versus gallons
43:17 oil, or leaders of gas versus of oil, etcetera. And if
43:22 think about it, um you gas at the surface is far less
43:29 , so it's gonna fill a lot volume. So, these, you
43:35 , gas oil ratios may be measured the thousands, Right? Uh just
43:43 the same volume of gas at the occupies so much more volume, or
43:49 the same number of gas molecules, say at the surface occupies four more
43:54 volume than it did dissolved in the in the subsurface. Okay, so
44:01 to make sure we're all clear on terminology, dissolved gas is an oil
44:08 mixture. It's a solution as a liquid phase. So we have one
44:17 , on the other hand, free exists as a separate face. It
44:22 as bubbles that may be floating in in the oil. Uh So the
44:28 and gas are distinct phases. So we have a two phase just dead
44:35 is when the solution gas has So we brought it to the surface
44:42 most of the gas is gone. come out of solution has gone below
44:47 bubble point has come out of solution it's either been separated out or
44:53 Uh huh. Some parts of the , they flare it because the gas
44:58 not worth selling. So they just it right there. Uh Not very
45:04 sound. Live oil. The dissolved is kept in solution. Now to
45:12 measurements on lie boil in the Uh You have to take a pressure
45:20 sample. So you take a sample c. two of the fluids and
45:29 that's that equipment maintains a constant pressure to slumber J here, they call
45:38 pressure compensating equipment. Mhm. And so you can control keep that,
45:46 that That fluid that live oil under c. two conditions. Or you
45:56 recombine the fluid. Uh You could that's what happens when for the laboratory
46:04 . Because those precious samples are pressure precious, right? So they're expensive
46:12 acquire. And they're they're not convenient deal with. So sometimes the gas
46:19 oil, it just recombined at pressure the laboratory. Okay, just another
46:30 of this uh compression of velocity of fluids measured as a function of
46:36 These are thousands of PSC Again at different temperatures. So we have heavy
46:44 here and you can see that at pressure in lower temperature, they could
46:50 significantly faster than water here. Water have a relatively small change with temperature
46:58 to the hydrocarbons. Uh and a smaller change with pressure. Here we
47:06 a light oil but it's a dead . So the gas has come out
47:12 solution and it could be a high , it could be similar, high
47:18 , low temperature could be similar to . The light oils can be uh
47:24 high temperature could be much slower than . But of course the lie
47:30 especially at high temperature can be very slower than water. And uh
47:43 I don't have a plot of oil is versus gas oil ratio. Oh
47:52 . What I do have is density gasol ratio. I should make that
47:58 at some point. Um But I have reservoir density or the oil
48:06 versus uh gas oil ratio. And can see that we could go into
48:12 thousands on gas oil ratio. And for det oils with that have a
48:22 low gas oil ratio. There's a dependence of the density on the api
48:30 . But as we move to significantly gas oil ratios. Uh and these
48:36 not unreasonable ratios. Uh we find little dependence on on the gas
48:47 So, where's that oils? We talking about .8 as a typical number
48:52 live oils. We could be down are significantly lower .6 would be if
48:57 had to come up with a number a high G. O.
49:02 Oil. Oh, now, moving to brines brian's are an interesting compound
49:16 they're polar. I mean, think it. You freeze water and you
49:21 the density, you expand it. right, That's why icebergs float.
49:27 um and that has to do with fact that the it's not a straight
49:33 . You know, H. H. Uh there's actually an angle
49:38 that bond. And so uh electrostatic , you have the charge. You
49:46 , the electrons are not evenly distributed around that molecule. So, oddly
49:54 , at low temperatures, you increase temperature and you make brian less compressible
50:01 least uh for freshwater, for fresh effect is less significant for very saline
50:10 and high pressure. But you start deeper in the earth. And then
50:15 have the same kind of systematics that saw before for the oil and gas
50:21 the higher the temperature, you you expand the rock. Excuse
50:26 You expand the fluid. And so make the fluid more compressible. And
50:33 , uh The same way the oil and gas gravity created a range of
50:41 I you have the same thing, with the salinity. So here's salinity
50:45 parts per million, 300,000 is not unreasonable salinity. We do reach that
50:53 the gulf coast at death. uh and look how high these module
51:00 can get. Remember I said that temperature and pressure uh 2.5 giga pascal's
51:08 be a a typical water value And you could get even lower uh
51:15 for fresh water. But look, I get more and more sailing,
51:20 a huge range. And this is ignored by geophysicist. People like to
51:26 use that number at 2.5 pick of . Well, it's a it's extremely
51:33 and that actually makes the hydrocarbon effect than one might think. Because the
51:42 between a saline brine and hydrocarbons can big. In fact, the contrast
51:52 a saline brine and fresh water can big. So, actually, in
51:57 studies, if you're looking for fresh , that is the potential use of
52:04 . Uh If you could control for rock properties uh seeing that big change
52:09 modules, uh distinct might distinguish uh salinity and brian density is pretty
52:22 It acts pretty much the way we they would. Um So again,
52:30 celebrities uh and and they're grouped by that seems to be uh pretty dominant
52:40 . Yeah. And it seems to bigger than the pressure effects that we
52:45 low medium and high pressure here. salinity is a real swinger and then
52:51 mono atomic change with temperature. Now, typically we have big variations
53:04 salinity with death. So, for , here is a gulf coast.
53:12 you have a gradient of 36 parts million. But so uh we're pretty
53:18 near the surface. But as we deeper and deeper, the salinity gets
53:24 and greater. So here, not deep, We're at 300,000 parts per
53:30 already. All right. So, , salinity is important. And you
53:37 a much higher gradient in California. , I need a hypothesis then why
53:46 you think salinity should increase with And why the big difference between the
53:51 coast and California? Oh, mm . Yeah. Does it have anything
54:13 do with the Mississippi uh suggesting more influx of freshwater? Right. Uh
54:24 that explain why it increases with No. Okay, that's the difference
54:32 California and? Well, I you know, fresh water starts at
54:36 surface. Right. And but there's else going on, which I think
54:44 even more important. It would be the, like the rivers bring in
54:52 that crystalized or something. Mhm. so, um you're suggesting more
55:02 the deeper you are, the older are, the more opportunity to saying
55:10 like that, the gulf coast would um more saline than helpful.
55:22 Because of the precipitation from the river's in the gulf at the surface?
55:32 . And then that's why would that why you have such a rapid increase
55:38 salinity with death in California? that might explain the difference between uh
55:47 coast in California. Could it have to do with tectonics? And
55:55 I think it has everything to do tectonics. Uh so remember if you
56:02 to dissolve salt in water, Isn't it better to heat the
56:09 Right? And they tell you to with salt and warm water? Why
56:14 they tell you to use warm Because you could dissolve more salt?
56:19 , I think that a dominant factor is the geothermal gradient, uh the
56:27 the temperatures, the more assaults you dissolve. So the higher the salinity
56:33 the waters and at plate boundaries, have hired your thermal gradients.
56:39 that's my hypothesis. That's what I'm . Uh, I was just looking
56:44 hypothesis. I don't know what the answer is. Uh these are just
56:48 at, at this point, maybe someone could do some reading on
56:54 . But again, I'm just always for opportunities for you to formulate
57:01 Okay, um moving on, we pretty excited when we found in the
57:12 engineering literature, we found a relationship both module lists and temperature And this
57:26 this this would be uh from uh engineering fisherman. So, these are
57:31 module I mm. And a strong on the amount of dissolved gas in
57:42 . These are brian's. Right? , no. So it's a gas
57:48 ratio. Right? So no So this is a pure water.
57:55 as we add more gas. Look how much, look how tremendously the
58:02 is, is decreasing. Uh we extremely concerned about this because it was
58:09 us that maybe the contrast and module between a gas reservoir and the brian
58:16 reservoir. It's not as big as think this could suppress the hydrocarbon
58:24 Um and then we realized we were in this thinking and the reason we're
58:36 is because this these data were obtained , where the data used to establish
58:45 relationships were obtained for pure water. what we found is we could not
58:52 serious gas dissolved into brian's. So we thought this was going to be
59:00 important effect and um decided uh that was not anything we had to worry
59:13 . Uh by the way, here some examples of velocity versus api gravity
59:20 this would be for, for dead . Uh the dash line is what
59:27 get from the PVT relationship or you say the equation of state. So
59:33 uh huh uh static measurements And these the kind of relationship we get for
59:40 of the dynamic measurements. So there , does seem to be a significant
59:52 which moves us on to the next of complication. And that is dealing
59:59 phase relations. It's not anything we to worry about what the solids we
60:05 dealing with but with the liquids and , it's a big deal, for
60:10 , a typical uh situation. This be like for example, water might
60:17 a relationship like this where if we at a pressure versus temperature diagram,
60:23 would have lines uh separating uh the phases. So at a given pressure
60:34 get up to, okay, let's here and give them pressure we get
60:37 to. Uh So this wouldn't be by the way. Uh We get
60:42 to a certain temperature and will melt solid and we'll get up to another
60:50 and will vaporize the liquid and it become gas. Right? So that's
60:55 typical. But some materials like dry , for example, CO2, you
61:01 be under certain conditions where you go from solid to gas. Right?
61:08 uh this is a what is called phase diagram And between liquid and
61:16 there's a critical point where you go to high enough pressure where you go
61:20 a high enough temperature and there is distinction. You wouldn't have uh you
61:27 have won what is called a supercritical . It might have more gas like
61:33 , might have more liquid like Uh But uh if you had a
61:39 , well, when we go to , you'll see that a given pressure
61:44 temperature, you might have two but this will be one phase beyond
61:49 critical point. So here we have mixture. Right? So we
61:56 you know, in a typical you have more than two compounds.
62:01 ? But let's say it's it's only compounds at this point. Um
62:07 What you have is if you look this pressure temperature relationship, you have
62:13 coda here or an envelope here above you have just one phase. So
62:22 , all this region here, we one phase is called a supercritical
62:28 Over here we're acting more like a . We might call this black
62:34 The same composition fluid at low pressure high temperature might be acting like a
62:41 gas. Alright, so this module is going to be very different here
62:45 here, but it's all one Now, if we start with this
62:52 black oil and we dropped the pressure we could get some gas coming out
62:59 solution. So we start producing This is called the bubble point.
63:06 here these percentages are the liquid volume this two phase region. So within
63:14 envelope here it's two phases. We liquid and gas. So we dropped
63:22 the bubble point. We have a bubbles coming out. So it's mostly
63:28 . All right. Now, this not a pure material. So we
63:31 have what is a critical point. have what is called a pseudo critical
63:37 . Now, if I go up the pseudo critical point, we have
63:41 is called the dew point. This at which you cross and exalt bubbles
63:46 called the bubble point. And this is called the dew point. Like
63:52 in the morning. Right. You condense liquid out of the air.
63:57 what do is you go outside and see droplets of water on your plants
64:04 so forth. Uh That's because you've the temperature during the night. And
64:13 you are exalted uh liquid from the here. So you've got some small
64:22 volume in this two phase region as heat up uh that all evaporates that
64:29 back into the atmosphere. Right. the same thing happens with in an
64:35 reservoir or a gas reservoir, you've this super critical fluid here and you
64:42 the pressure from here. They're there drop the temperature from here there and
64:48 condense liquid out of the gas. we have a supercritical fluid here.
64:57 is called condensate. A gas condensate when we bring this stuff up to
65:03 surface, uh I'm going to get liquid exalting down. So, um
65:11 that would be our valuable conferencing. , I think I'm gonna stop
65:18 We'll talk more about phase relationships next . Are there any questions, Is
65:24 all perfectly clear to you? Do think about it? And if you
65:31 to think about it or if you're trouble with some of the concepts,
65:35 ask me, I'm happy to repeat because I don't always explain it the
65:41 way, the first time around. the way, I think about the
65:45 Critical point and think about what happens your reservoir is very close to the
65:51 of critical Point, in which changing pressure a little bit like producing
65:57 reservoir could produce wildly swinging combinations of here. All right. So,
66:07 , um, think about these phase and, uh, let me know
66:14 you have any questions about it, I'll pick it up here next
66:19 All right. Thank you
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