| 00:02 | this conference. This conference will now recorded. Okay, so velocities decreasing |
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| 00:13 | increasing temperature, you increase the The fluids expand. They become more |
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| 00:21 | . These happen to be heavy oils so they are more susceptible to this |
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| 00:28 | this temperature range than for example brian be. But here you have velocity |
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| 00:35 | as pressure is increasing. Can anybody that? All right. I'll leave |
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| 00:47 | for you to chew on also and come back to such slides until you |
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| 00:54 | decide you want to start thinking, to have to do with the fluid |
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| 01:01 | . Assume these 100% oil saturated. it strike you as odd. That |
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| 01:15 | is decreasing as pressure is increasing. thought it would be opposite because you |
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| 01:21 | , as pressure increases, you have microfractures are revealing. Right? So |
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| 01:28 | do you think is going on here ? I said this was an inadequately |
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| 01:34 | slide. Is the pressure increasing creating more fractures? I don't think |
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| 01:44 | what's happening here. Um I think guys are participating. I'll go ahead |
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| 01:49 | tell you what I think is going . I think the pressure is not |
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| 01:56 | correctly. They haven't specified what type pressure and they never said it was |
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| 02:02 | pressure, overburden pressure or external I believe it's poor pressure. |
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| 02:08 | as the poor pressure is increasing the go down because the fluids are pushing |
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| 02:16 | rock frame more open, is pushing poorest to be more open and therefore |
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| 02:22 | compressible. This was a famous paper akin to more on the effective temperature |
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| 02:35 | velocities in Baria sandstone, which is classic sandstone that rock physicists love to |
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| 02:42 | measurements on because it's porous, but well lit defied and it's very |
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| 02:48 | So you don't have nasty clay's interfering things. And he measured p wave |
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| 02:54 | with increasing temperature. He also measured wave velocity with increasing temperature and he's |
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| 03:01 | three different p wave velocity curves there different differential pressure is also different confining |
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| 03:10 | pore pressures. But as the differential is increasing, you get you go |
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| 03:17 | the higher curve. Alright, so the velocities are increasing with a differential |
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| 03:26 | . And that's true for both P and share waves now for p |
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| 03:31 | Remember we said as the temperature increases rockies, the brian becomes more |
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| 03:40 | so the velocities go down, that's . But what about shear wave |
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| 03:47 | Should shear wave velocities be dependent on ? And if you look at the |
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| 03:52 | wave velocity curves at the high differential , there is essentially no dependence on |
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| 04:01 | ? Excuse me, on temperature. the two curves at lower differential pressure |
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| 04:09 | suggesting a temperature as that velocity share decreases as temperature increase. So, |
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| 04:20 | anybody want to hypothesis why that might happening? Could it tie back to |
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| 04:31 | viscosity of the fluids in the Probably not in the case of |
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| 04:40 | What do you think about fluids expanding temperature? What might happen is the |
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| 04:46 | expand that increase uh, increase our pressure or we have differential pressure. |
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| 04:54 | yeah, they're controlling the four pressure . So what they do is they |
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| 04:58 | a little tube into the sample. miraculous that they could do this. |
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| 05:04 | they are controlling the external temperature. with this tube into the sample they |
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| 05:11 | control the poor pressure as well. put a pressure gauge on that and |
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| 05:15 | let fluid bleed off as necessary until got the desired pore pressure. So |
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| 05:24 | you see pc is the confining pressure PP is the poor pressure. So |
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| 05:31 | high pressure there's no dependence on temperature at low pressures there seems to be |
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| 05:37 | dependence on temperature. Now, if remember our velocity versus pressure terms what |
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| 05:44 | true at lower pressures or what is about the rock and low pressure versus |
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| 05:50 | pressure. The degree of ratification. , if defecation, I would you |
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| 06:06 | , I would say the compressibility of frame is different. With indication implies |
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| 06:11 | geological process. Right? So I the rock. It has a degree |
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| 06:16 | lymph indication. Then I put it the laboratory. I may change things |
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| 06:21 | the rock frame as I squeeze it I put fluids in and so |
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| 06:25 | I may alter the rock frame. I wouldn't call that changing the degree |
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| 06:31 | litigation. That's a geological process. yes, it seems to me that |
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| 06:37 | is certainly affecting the module lists of frame because the velocity is going |
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| 06:44 | the sheer velocity is going down. it suggests that the frame becomes less |
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| 06:50 | and higher temperatures. Why might that ? But this only happens at low |
|
| 07:00 | . There's more of something in Iraq low pressure than at high pressure. |
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| 07:04 | talked about this at length yesterday louis ? Well, it's all water |
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| 07:15 | Right. So all of these uh know, this is in the laboratory |
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| 07:22 | so the pore spaces filled with water . Yes. Or as opposed to |
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| 07:35 | , let's just say low aspect ratio or poor. Is that act like |
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| 07:40 | aspect ratio? Of course. Remember low pressure, your flat pores open |
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| 07:47 | and at high pressure they close. ? So if the flat pores are |
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| 07:53 | closed, then the rock frame is going to be changing its virginity as |
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| 08:02 | change the temperature of the fluid. module at the both modules of the |
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| 08:06 | is changing, but that doesn't change rigidity. And all the flat pores |
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| 08:11 | closed because you're under high confining But at low pressure the flat pores |
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| 08:19 | the flu is expand. The flat may open up more alright, There |
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| 08:24 | be partially open and the flu is and it pushes them further open. |
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| 08:30 | that could be what's going on. However, if you look at these |
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| 08:39 | , these trends don't seem to be strong. In fact, if I |
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| 08:45 | one data point here, that trend almost flat and this trend, there's |
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| 08:52 | data over the low temperature range, doesn't seem to be a big effect |
|
| 08:57 | . I don't know how these lines to the data, but it's possible |
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| 09:03 | the slope on those lines is not significant or is being biased by this |
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| 09:11 | error, possible experimental error here. Anyway, so either the data is |
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| 09:19 | exactly right or we do have a to explain it. Now, of |
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| 09:29 | , as we go to very low , we can freeze the fluids. |
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| 09:35 | this is problematical thing in arctic regions the north slope of Alaska. Uh |
|
| 09:45 | . What you have then is a velocity zone at the surface where the |
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| 09:49 | are frozen now in spring. As start to thaw, you may have |
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| 10:01 | of frozen grounds and you may have of unfrozen ground can produce terrible near |
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| 10:08 | effects. Also when the permafrost is , uh, you can't really run |
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| 10:17 | trucks through this uh mud. So seismic acquisition a season is in the |
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| 10:29 | when the ground is solid and you run trucks over it. Now the |
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| 10:42 | of the water decreases. But that's , you know, that's not the |
|
| 10:47 | reason for this change in velocity. what could cause such a big increase |
|
| 10:53 | velocity as you freeze The water in four space? What happens to the |
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| 11:02 | as you freeze it sacrifice it solidifies that makes it harder to compress. |
|
| 11:11 | actually has resistance to compression and it makes it rigid. So in |
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| 11:19 | you're going from a porous medium. a mixture of solids and liquids when |
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| 11:26 | water has melted to a mixture of and that gives you a higher |
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| 11:38 | Does the same thing apply to gas ? It does. Now, later |
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| 11:55 | in the course, we will look the mathematics of changing the fluids in |
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| 12:01 | porous rock, but for the time , we're just going to look at |
|
| 12:05 | phenomenal. Logically, I have a frame and I stole this slide from |
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| 12:11 | Hiltermann. You can't you can't see uh annotations. The citations are cut |
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| 12:20 | for some reason. So you're not it, but this is from fred |
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| 12:26 | and many geophysicists like to draw rocks swiss cheese. I figured out why |
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| 12:32 | the case. So, here the is the ferocity and the gray is |
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| 12:38 | solid material. But anyway, you the idea, it's a it's a |
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| 12:43 | medium and there are various properties of medium that are important to us. |
|
| 12:51 | huh. The bulk module lists or to volumetric compression of the whole |
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| 13:00 | It's a solid matrix is a rock and it's fluids in the poorest |
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| 13:08 | The bulk modules of that whole thing called K. Sat that saturated |
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| 13:16 | So the module lists of the rock with fluids and that's the module |
|
| 13:22 | would measure, say with the sonic , measuring the PVS and density and |
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| 13:27 | out the bulk modules. That would the saturated module is with the institute |
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| 13:34 | . The solid material could be called matrix that some some sometimes called K |
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| 13:40 | KM. A. Also sometimes K , sometimes Ks. One of the |
|
| 13:47 | favors I did for you in this is I did not unify the notation |
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| 13:53 | the notation is never uniform. It all over the place. So you |
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| 13:57 | to kind of figure out for yourself what the notation is as we move |
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| 14:02 | equations. It's not because I was lazy to fix all these figures. |
|
| 14:08 | wasn't bad at all. It was service that I was providing to you |
|
| 14:13 | letting you adjust to the way the world is with notation bearing all over |
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| 14:19 | place. Okay. The liquids in fourth space or fluids, it could |
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| 14:25 | gas or liquid would be K fluid K. F. L. Or |
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| 14:30 | . F. But a very important is something that we have to |
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| 14:37 | We have to back out using theoretical is what is called K Dry. |
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| 14:45 | I hate that terminology. What K is, is the bulk modules. |
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| 14:49 | rock would have without the fluids. is a horrible idea. Because if |
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| 14:58 | take the fluids out, you could the interaction between the fluids and |
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| 15:03 | You can actually change the rock. slaves could clays could change their mechanical |
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| 15:14 | . Uh There can be geochemical effects the rock is exposed to different |
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| 15:19 | Iraq exposed to brine may cement very than Iraq exposed to uh or saturated |
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| 15:28 | oil for example, oil may preserve porosity, whereas brian would allow the |
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| 15:34 | to be cemented up. Also this of K Dry, it's an instantaneous |
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| 15:41 | , It's a mechanical thing. So I'm mechanically take the fluid out. |
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| 15:48 | doesn't suggest what will have happened over time with different fluids in the |
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| 15:55 | Write a dry rock over geological time compress and compact more easily than a |
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| 16:02 | saturated rock for example, or the saturated rock could be more lubricated. |
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| 16:09 | game grains are lubricated and they'll slide each other differently. So all kinds |
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| 16:15 | things can happen. Uh The rock the fluid in it. The rock |
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| 16:20 | itself could be harder or softer depending the fluid in the rock. But |
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| 16:27 | equations of physics don't comprehend all which is why we have to use |
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| 16:34 | equations with a grain of salt. ? So I don't like the terminology |
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| 16:38 | . Dry. I would rather call the frame module list or the skeleton |
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| 16:45 | . It's the bulk modules of the frame in contact with the fluids geologically |
|
| 16:51 | geo chemically in contact with the Is it contact with. Um So |
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| 16:57 | hear me referring to this as the modules but usually in the literature, |
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| 17:02 | referred to as K dry all of are volumetric module I so the ratio |
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| 17:11 | volumetric stress to volumetric strain. So can go through the math and we |
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| 17:23 | now you will do a little bit math in this course. It's not |
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| 17:26 | . Mm but if we go through math, we could then change the |
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| 17:35 | in the rock or we could change water saturation in the rock. So |
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| 17:40 | I have kate frame, I now the module lists of the fluid. |
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| 17:47 | so here, I calculate an effective . It's as I add gas to |
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| 17:52 | rock. And how would I do ? How would I put gas bubbles |
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| 17:57 | water and compute the modules of that medium of a gas water mixture where |
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| 18:05 | gas is free as bubbles. You have the equation to do that. |
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| 18:10 | equation is that? Well, you have many equations. I haven't given |
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| 18:30 | that many which one might be which computes the both modules of a mixture |
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| 18:40 | on the bulk modules of the both I and fractions buying fractions of the |
|
| 18:50 | . Aspirins? Well, I haven't you gasoline yet. Right. |
|
| 18:55 | um, here, but I've already you equations where I can calculate an |
|
| 19:02 | modules or things. So, which have I given you the masked man's |
|
| 19:10 | , that's density, that's not that's both modules because that's the plane way |
|
| 19:19 | , what about the plane wave So I I got say I've got |
|
| 19:25 | constituents solid and water and I've got in the water. Solid floating in |
|
| 19:34 | water. So I have solid grains in water. What equation do I |
|
| 19:39 | to calculate the modules of that What is that mixture called? I |
|
| 19:56 | solid grains floating in a liquid That's a suspension. Do you recall |
|
| 20:05 | told you how to calculate the module of the suspension. Does it have |
|
| 20:12 | do with a critical porosity? well, it has to do, |
|
| 20:19 | . It has to do with what do when you have exceeded the critical |
|
| 20:23 | . If that's what you're getting You guys got to catch up on |
|
| 20:33 | homework. I mean, if already on there were homework assignments where you |
|
| 20:41 | supposed to plot that, she was to plot the bulk module. I |
|
| 20:46 | we vary, vary the volume fraction constituents. Right? So, um |
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| 20:54 | me just say that if I have mixture, if I have a suspension |
|
| 20:58 | solid material in a liquid, I use the Royce bound to exactly calculate |
|
| 21:07 | module us. That's also called Woods . I think we covered that maybe |
|
| 21:12 | the first class. And it turns if I have gas bubbles in floating |
|
| 21:21 | a liquid, I could still use equation. So it's a volume weighted |
|
| 21:27 | average of the modules of gas and modules and liquid. So that allows |
|
| 21:35 | to calculate the fluid module. Us I dropped the fluid module is what |
|
| 21:40 | happen is when we go through gas equations will see the velocity of the |
|
| 21:46 | drops. The shear wave velocity doesn't because it doesn't depend on the fluid |
|
| 21:52 | is per se. Right. The frame may change as I change the |
|
| 21:58 | , but if I'm just mechanically changing fluid module is and that's all I'm |
|
| 22:03 | . The sheer modules hasn't changed. I add guests and the shear wave |
|
| 22:08 | goes up. Why is that why the shear wave velocity go up if |
|
| 22:16 | at gas? Is it because I'm the sheer modules because decreases density. |
|
| 22:42 | . That's exactly what happens if I'm affecting the share module is density is |
|
| 22:46 | only other thing that could be I dropped the density, the velocity |
|
| 22:51 | up. Now, what happens is I take a reciprocal average of the |
|
| 23:00 | modules, the bulk modules to the drops way down when they had just |
|
| 23:05 | little bit of gas. Remember, the most compressible material that dominates the |
|
| 23:12 | average. The p wave velocity comes up as I had more gas because |
|
| 23:17 | haven't dropped both modules anymore. It's dropped that as far as it's going |
|
| 23:21 | go and now I reduce the density the p wave velocity comes up. |
|
| 23:29 | think about the D P. S ratio, The V P. |
|
| 23:31 | . S ratio. I had a bit of gas VP over V. |
|
| 23:35 | drops dramatically and then remains relatively constant this ratio is relatively the same. |
|
| 23:48 | , so this is a theoretical computation gas masks equations which will study in |
|
| 23:55 | few weeks, but I love One can rather than going through the |
|
| 24:08 | of the theoretical Gassman equations and there's lot of uncertainty in the way errors |
|
| 24:14 | through those equations. One can just huh. Cross plot brian stand velocity |
|
| 24:23 | gas stand velocity better trend to So, it's basically what I did |
|
| 24:29 | , which was the black curve, don't have the data points to show |
|
| 24:33 | , but I have the curve that released, the data points didn't. |
|
| 24:39 | the red line here is the So if the brian stand velocity equals |
|
| 24:44 | gas man velocity, you're on the line here. And what you can |
|
| 24:51 | is that the brian stand velocity is faster than the gas hand velocity, |
|
| 24:56 | least for typical rocks for granular sand . We're talking about sand stones |
|
| 25:04 | we're always below the line. So to the right, I should |
|
| 25:07 | to the right of the line where brian sand velocity is higher than the |
|
| 25:11 | sand velocity, But as we get very high velocities, that difference is |
|
| 25:18 | small. It's just a couple of . A few percent. Whereas I |
|
| 25:24 | to very low brian stand velocities. gas effect is really big. |
|
| 25:29 | So here we're going from 2.5 to five. So we more than doubled |
|
| 25:36 | here and over here. It's just minor change percentage wise. Anyway, |
|
| 25:43 | , hypothesis why when I have low wave velocities, is the gas effect |
|
| 25:50 | much bigger? Is this related to we saw in the previous slide, |
|
| 26:03 | the compressibility changes quickly early on the gas percentages. Okay, so here |
|
| 26:12 | thinking we have all gas percentages. empirical. So on the average, |
|
| 26:17 | gas, the water saturation here is 50%. So we would more or |
|
| 26:23 | here on the curve. Okay, I'm saying is this difference from here |
|
| 26:31 | here is much bigger for low velocity and for high velocity rocks. See |
|
| 26:39 | . Okay, the drop from p velocity to so here I'm 6 to |
|
| 26:47 | . Right? So, p wave of six, gas velocity of |
|
| 26:54 | That's almost a factor of two. up here, What is it 19,000 |
|
| 27:02 | 18,000? Is that right, So, what is that? |
|
| 27:11 | Something like that? Oh, is difference, is that widening as we |
|
| 27:17 | like towards the very, very high ? Is there like a uh I'll |
|
| 27:21 | you hypothesize that I haven't come to yet. But yeah, good |
|
| 27:31 | The low velocity, It means probably like a higher porosity. Kind of |
|
| 27:38 | a Class three at the bottom. difference. Yeah, that's it. |
|
| 27:45 | local why, you know, these are low velocity. So their modules |
|
| 27:49 | low right there, High porosity Maybe not highly liquefied, etcetera. |
|
| 27:56 | , the rock frame is more So the fluid effect is much |
|
| 28:03 | If I have a very strong rock that is in compressible velocity is not |
|
| 28:08 | to care too much what's in the space. But if it's a very |
|
| 28:12 | rock space, as those poorest close fluids and if they can't escape, |
|
| 28:18 | going to resist that compression, they're to push back. Okay, so |
|
| 28:25 | this end. What about this Is that like the Class four dimming |
|
| 28:34 | in between class to kind of that zone? I'm not gonna related directly |
|
| 28:43 | the HBO classes first of all, beyond the scope of this course. |
|
| 28:47 | talk about the rocks themselves. Why might these rocks even though they're |
|
| 28:54 | velocity? Why might they have a effect? A bigger fluid effect than |
|
| 29:01 | ? These rocks? Mhm. Think a really hard rock. Right, |
|
| 29:13 | courts would be around over here. would be pure courts. How could |
|
| 29:20 | have a gas effect in pure It's a It's a courtside. It's |
|
| 29:29 | metamorphic rock. Could I have a effect in court, sir? In |
|
| 29:33 | port side, I guess if you like fractures in. Exactly. |
|
| 29:42 | That's exactly right. So, maybe after more low aspect ratio fractures that |
|
| 29:54 | have fluid in them to have that . Whereas maybe these rocks or more |
|
| 30:00 | reports. Right. Maybe uh there many fractures here because the velocities are |
|
| 30:08 | high. There are many, but depend very much the pores here depend |
|
| 30:15 | much on what's in them. Maybe are more ground pores here, which |
|
| 30:19 | why the velocities lower, but they care too much what's in that. |
|
| 30:30 | , so we're not going to talk HBO classes, but we are going |
|
| 30:35 | talk about uh the types of amplitude you get as we change the fluids |
|
| 30:44 | Iraq. So here we're looking at impedance density times velocity and here we |
|
| 30:53 | the impedance of shells. That's kind what we're comparing to my brian sand |
|
| 31:00 | the open circle. If it's lower penis in the shell, what's going |
|
| 31:04 | happen when I add gas? It's to be even lower, infuse. |
|
| 31:08 | going to lower the velocity, lower destiny. So I have even lower |
|
| 31:12 | people. So this would be a reflection coefficient. This would be a |
|
| 31:18 | negative reflection coefficient for the gas. what we call a bright spot. |
|
| 31:24 | the way, a rule of thumb could pretty much always rely on is |
|
| 31:29 | impedance drops when you add gas to . I've never seen a case where |
|
| 31:35 | didn't. Yeah, because, you , it's not only the velocity |
|
| 31:40 | it's also the density effect. And the density is dropping when you add |
|
| 31:46 | . So in this particular case my sand was hiring peters than my |
|
| 31:51 | So when I add guest to that , I lower density, I lower |
|
| 31:56 | , I lower the impedance. I a weaker positive reflection coefficient. This |
|
| 32:03 | called the vin spot here. So is a strong hard reflection. This |
|
| 32:08 | a softer or a weaker hard Right? That's the dem side. |
|
| 32:15 | then there are cases and happened quite where you know, brian san happens |
|
| 32:23 | be faster or higher impedance in the . You put gas in the rocket |
|
| 32:29 | its lower impudence in the shelf and a polarity reversal. So you switch |
|
| 32:36 | hard reflection to a soft reflection. what type of anomaly or you gonna |
|
| 32:49 | at a particular locality? Well, way to establish an expectation is to |
|
| 32:58 | rock physics trends versus death and this a lot of what uh people |
|
| 33:08 | rock physics and industry would do in particular location if they're going to study |
|
| 33:13 | types of amplitude anomalies. They're looking at, they will plot density brian |
|
| 33:21 | velocity, shale density, brian sand , gas and density versus death. |
|
| 33:28 | they'll fluid substitute using the mass balance . Right? So they'll change the |
|
| 33:33 | density and given what the brian stands doing, they can figure out what |
|
| 33:37 | gas sands are doing. Keep in these are average values versus death. |
|
| 33:43 | never going to be a perfect line this. But you know, consider |
|
| 33:46 | a regression fit of some kind and could do the same thing with velocity |
|
| 33:53 | in this case interval transit time uh shells, reading off the logs for |
|
| 33:58 | brian sands, reading off the logs then again a fluid substitution from brian |
|
| 34:04 | to gas sand. And that would using gas months equations which will talk |
|
| 34:11 | soon enough. So then you can at the average response as a function |
|
| 34:18 | depth in an area. So here white curb of swing or that reflection |
|
| 34:25 | is for the brian sand and the represents represents the reflection coefficient for a |
|
| 34:33 | . And you can see in all these cases in this area were not |
|
| 34:36 | deep. The brian sands are all reflection coefficients, they're all stopped and |
|
| 34:43 | gas stands are all more negative. all of these deaths would have bright |
|
| 34:50 | . I put gas in a rock I'm going to have a stronger negative |
|
| 34:58 | . Then if I have brian in rock. Mhm Okay, so here |
|
| 35:08 | have velocity versus death. This this from Gardner Gardner and Gregory again, |
|
| 35:14 | citation got cut off. So you'll this in their paper and I actually |
|
| 35:23 | a Gregory's dana, He was, was a research associate at the University |
|
| 35:28 | texas when I was a grad student at least to see some guy running |
|
| 35:33 | in the basement. We thought he the janitor. Until one day we |
|
| 35:37 | him giving a lecture in a graduate . Right? So that that was |
|
| 35:42 | Gregory. And he had thousands of points from thousands of wells in the |
|
| 35:49 | coast. And so he these trends an average of many, many data |
|
| 35:58 | . Uh huh. And again, just what they are. They are |
|
| 36:02 | you will have in any particular you will have deviations from these |
|
| 36:09 | will have a lot of scatter around trends, but these are showing on |
|
| 36:13 | average what happens in the gulf And again, we have our |
|
| 36:17 | so that this is death velocity. the rocks are compacting rapid for a |
|
| 36:23 | reduction rearrangement of brains, deformation of until it's pretty much as compacted, |
|
| 36:30 | going to be at which point it lit defying and it loses ferocity with |
|
| 36:37 | depth and pressure. Um none of rocks on the gulf coast or what |
|
| 36:43 | would call fully liquefied, right? uh the velocity increased with death becomes |
|
| 36:54 | . Mhm. Okay, so um got the shell trend which is a |
|
| 36:59 | continuous thing. It it doesn't have need right, with which when granule |
|
| 37:06 | with sands, you're going from loose is to uh denser and denser |
|
| 37:13 | Eventually you packed as much as you , shells are more continuous, you're |
|
| 37:19 | squeezing these books tighter and tighter and squeezing water out of the shells, |
|
| 37:26 | . So that tends to be a bumpy curve. Right for shells. |
|
| 37:32 | what you see is the brian velocity the shell very shallow here. The |
|
| 37:39 | are faster than the shells, but put a little pressure on the shells |
|
| 37:44 | compact and the shells actually for a get faster than the brine sands. |
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| 37:52 | but eventually uh the sands get compacted off and uh cemented enough such that |
|
| 38:00 | are faster than the shells on the . And then uh Greg Gregory did |
|
| 38:07 | substitution. He added oil here. added gas here. And you by |
|
| 38:18 | to first order, assume that density acting similarly to uh brian stands just |
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| 38:25 | the purposes of this question. Say was impedance instead of velocity and you |
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| 38:31 | curves like this. Where would you bright spots? And it would be |
|
| 38:37 | where the shells are higher impedance than sands. So in fact here for |
|
| 38:49 | and you might you might get dim . They have very similar impedance to |
|
| 38:54 | shells. Or you could have a polarity reversal here. Now, as |
|
| 39:03 | said, um these are just average and a particular death. You will |
|
| 39:10 | have a distribution. So these are that I took from our database that |
|
| 39:18 | had, this would would be an Louisiana area. It's just a particular |
|
| 39:27 | where we had a lot of wells again, I couldn't release the |
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| 39:31 | but I was able to release the grams. Right, So this is |
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| 39:37 | distribution of brian sand velocities, shale , gassing velocities. Again, the |
|
| 39:45 | dancer fluid substituted using gas mints You see a lot of overlap because |
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| 39:53 | distributions a particular gas hand maybe faster a particular brined stand at a given |
|
| 40:03 | uh huh. Death. How could could that be? Well, you |
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| 40:07 | have a very low porosity sand. , so poorest Grinstein may actually be |
|
| 40:13 | velocity than a non forest. So there's ambiguity. Right. This |
|
| 40:21 | one of the reasons we try to a video to reduce the ambiguity. |
|
| 40:27 | here, given the sand shell gas properties, we can compute the hist |
|
| 40:33 | gram for reflection coefficients. And what find again is this particular locality offshore |
|
| 40:41 | over that depth frame. All so, it's very specific. But |
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| 40:47 | you find is that on the the brine stands here in this area |
|
| 40:52 | a near zero reflection coefficient on the , where the gas sands on the |
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| 40:58 | have a large negative reflection coefficient. , we would expect on the average |
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| 41:03 | to have bright spots. However, that particular gas sands could actually have |
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| 41:12 | in fact, they even have a reflection coefficient and a particular gas and |
|
| 41:19 | uh higher or more positive reflection coefficient a particular brian's notice that that's not |
|
| 41:27 | fluid substitution. In fact, these two different rocks. Right, this |
|
| 41:31 | be a very porous brine sand and would be a very tight gas. |
|
| 41:44 | this is a plot from fred Hiltermann he's getting even more precise here. |
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| 41:50 | showing actual hissed a grams for sand and shale velocity versus death. This |
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| 41:56 | also an offshore Louisiana area and you there's a lot of spread around the |
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| 42:05 | value. Are these asterisks here? , right, there's a lot of |
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| 42:11 | more so in the sands than in shells. Okay, now, but |
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| 42:20 | you take these average values and you these versus death. This is a |
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| 42:26 | from norman idol. What he's got his brian sands where shallow there are |
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| 42:34 | reflection coefficient. There's what he calls crossover death. Yeah, you go |
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| 42:41 | than that and the brian stands on average have a positive reflection coefficient. |
|
| 42:48 | you do fluid substitution. And so gas hands are always plotting here at |
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| 42:53 | impedance than the brian stand. Some negative reflection profession. So down to |
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| 43:00 | crossover point, you will have bright between this crossover and the point at |
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| 43:08 | gas crosses over the brian sands are to be positive reflections. Gas sands |
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| 43:13 | negative reflections and you are polarity reversals after gas becomes high impedance than brian |
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| 43:21 | and gas sands above positive reflection These are dim spots worked in |
|
| 43:32 | Now, needle has added a couple dash lines here, what are these |
|
| 43:38 | lines? Well, he's suggesting, we talked about gear pressure and if |
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| 43:43 | go into gear pressure here, pressure reduce the velocity and density of the |
|
| 43:50 | . So that will lower the impedance the shell. So the wet |
|
| 43:55 | if we lower the impudence of the to here, you know, it |
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| 44:00 | be uh geo pressure does that then crossover will occur at this step. |
|
| 44:07 | so you'll have bright spots above The same thing for the Dench spots |
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| 44:12 | will be moved up. Typically the pressures or the shale velocities are more |
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| 44:20 | by poor pressure than the sand velocities the shells are more compressible. So |
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| 44:26 | poor pressure has a bigger effect on frame modules. So you could plot |
|
| 44:36 | these crossover points are going to be rocks of different ages. And this |
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| 44:43 | also applaud from norman Idol. And just dividing, he's saying, what |
|
| 44:51 | will the crossover point occur at for of different ages? So, on |
|
| 44:58 | axis you have the age. uh it turns out the older the |
|
| 45:06 | , the shallower at which this crossover is going to be. So apply |
|
| 45:11 | to seeing rocks, you may never this crossover, right? But |
|
| 45:15 | it's going to be at a great uh in older rocks. Uh you |
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| 45:20 | have that positive reflection coefficient for brian and much shallower deaths, which means |
|
| 45:27 | need to be looking for polarity reversals much shallower deaths. Okay, that's |
|
| 45:38 | I have on velocities. Are there questions on velocity or compression? Wave |
|
| 45:48 | ? Okay. I'm gonna stop And I'm going to share again. |
|
| 46:02 | don't have a question. Yes. the name again of this? It's |
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| 46:06 | for the larry king. What anytime, regardless of selection? |
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| 46:12 | neidl cause that the calls that the deaths. Thank you. Okay, |
|
| 46:23 | the next unit R V P. s ratios. Right? So until |
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| 46:28 | we've been talking primarily about p wave . Now we're gonna throw shear wave |
|
| 46:36 | into the mix. And look at ratio of the two. And you |
|
| 46:41 | see there is a direct relationship between V P B s ratio and Madison's |
|
| 46:47 | as we discussed previously. So, to review what is Parsons ratio When |
|
| 46:53 | have a fluid in family? The is infinity. What is Pakistan's ratio |
|
| 47:13 | or 0? The other side. . Remember infinity squared minus twos. |
|
| 47:24 | squared is infinity. To infinity squared two is to infinity. So infinity |
|
| 47:30 | by twice. Infinity is .5. Castagna math. A two mathematician would |
|
| 47:36 | the limit of this relationship. S limit as V P B s approaches |
|
| 47:43 | And that is equal 2.5. All . So, a person's ratio? |
|
| 47:50 | is fluid. What's the minimum? ratio? Somebody said -1? That |
|
| 47:57 | the minimum. Hassan's ratio. Uh somebody want to do some quick algebra |
|
| 48:02 | telling me what the V. D. S ratio is. When |
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| 48:07 | ratio is minimum, One person's ratio -1. Was it a square |
|
| 48:38 | 4/3? That's exactly right. Really . Okay so square to 4/3 is |
|
| 48:47 | . We'll see that again. So yell when you see it again and |
|
| 48:51 | give you another point on your The first one to yell. Uh |
|
| 48:57 | get an extra point on your So. Okay. That's the theoretical |
|
| 49:02 | up with songs ratio. That that the material that gets thinner as you |
|
| 49:08 | it. Which is very rare practical limit of Hassan's ratio is zero. |
|
| 49:15 | I haven't seen rocks where I believe seen ratios less than zero. So |
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| 49:22 | range of persons ratio is 02.5. so remember the definition of Hassan's |
|
| 49:35 | Sometimes we include a minus sign. we don't all depends on how you |
|
| 49:40 | your coordinates whether delta W. Is or positive. So let's not worry |
|
| 49:46 | that. But it's the transfer strain by the longitudinal strength. Yeah. |
|
| 49:52 | uh you could represent it in terms the BPB aspirations and just to give |
|
| 49:59 | the same equation in a slightly different . So V. S. |
|
| 50:05 | P ratio in this case. Or can calculate the dp B s ratio |
|
| 50:10 | this equation uh sticking. Hassan's So what is uh the V. |
|
| 50:17 | . B. S ratio when lessons was zero. Did you say was |
|
| 50:33 | ? Or thirds or something like No no no. And let put |
|
| 50:39 | ratio B zero many more square into . So the practical lower limit of |
|
| 50:54 | V. P. V. S is the square of two. And |
|
| 51:02 | said last time there's a 1-1 relationship the D. P. B. |
|
| 51:06 | . ratio and fastens ratio. So over the the practical lower limit to |
|
| 51:14 | maximum value. And so 1.41 is smallest v. PBS ratio. And |
|
| 51:22 | I know persons ratio, I know PBS and vice a versa surges by |
|
| 51:27 | into the equation. And remember we about there was a debate in literature |
|
| 51:32 | leon Thompson and some uh some others example, fred Hiltermann likes to use |
|
| 51:37 | ratio. Leon likes to use the PBS Trecia. I think it's a |
|
| 51:42 | of preference. If I'm dealing here very high of persons ratios, it |
|
| 51:49 | very insensitive to big changes in the PBS ratio. So it's more convenient |
|
| 51:54 | very soft unconsolidated rocks that are more like in their behavior. Higher the |
|
| 52:02 | ratios, higher plaisance ratios. Um you use the PBS station. |
|
| 52:09 | if you are in well with if with Lovie PBS ratios you may see |
|
| 52:14 | bigger change in essence ratio. Now on. Uh fellow professor at Colorado |
|
| 52:27 | of mines published that George pickett published work. He did. I believe |
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| 52:31 | was also a chow, A tremendous of this rock physics work was done |
|
| 52:37 | shell probably 20 years ahead of the of the industry. Um And he |
|
| 52:43 | that there is a little illogical dependence the T. PVS ratio. So |
|
| 52:48 | he had uh was looking at sonic . So he's looking at sonic transit |
|
| 52:55 | . Microseconds for feet. So shear slowness versus P wave slowness. And |
|
| 53:01 | noticed for lime stones, he had pretty constant be PBS ratio of 1.9 |
|
| 53:07 | for Dolomites pretty constant. Be PBS 1.8. But stan stones, he |
|
| 53:14 | the PBS varying and she got The D. P. B. |
|
| 53:17 | increased. But basically he said somewhere know little uh south of 4.6 to |
|
| 53:24 | little bit over 1.7. And that uh the rule of thumb in industry |
|
| 53:31 | 1.6-1.7 for Sandstone, interestingly, he had some limey sands here which were |
|
| 53:42 | or yeah, he had it was mixture of limestone and sandstone I should |
|
| 53:47 | cal setting course and he had some license ratios there or be PBS ratio |
|
| 53:54 | there. Now if we look at pure minerals for calcite, we have |
|
| 54:07 | grouping of points. These are measurements calcite crystals Up there around 1.9-2. |
|
| 54:15 | in there for Dolomites we find a range and that's not completely understood. |
|
| 54:23 | think it has to do with the of cat irons. Right, so |
|
| 54:29 | is calcium, magnesium carbonate. You have more magnesium and calcium or calcium |
|
| 54:37 | neck than magnesium. And you could iron substitution. So what is called |
|
| 54:43 | may not be 5050 calcium and And so there's a wide range And |
|
| 54:51 | averaging around 1.75. Um Remember pick had in dolomite rocks. He had |
|
| 55:01 | And then course is pretty well The PBS ratio close to 1.5 |
|
| 55:10 | Now what do we mean by the velocity? Keep in mind we discussed |
|
| 55:16 | previously where the mineral velocities depend on . These minerals are anti psychotropic. |
|
| 55:24 | depending along which access you're making the and how your share wave is |
|
| 55:31 | uh perpendicular or parallel to which access get different velocities. So what is |
|
| 55:39 | by the mineral velocity? What is is an idea? Tropic, randomly |
|
| 55:46 | distribution of crystals with zero porosity. , a mineral velocity is kind of |
|
| 55:54 | fiction right? It doesn't really exist nature. Right? Mm. So |
|
| 56:04 | forcing it to be Aisa tropic and and that's the number we use to |
|
| 56:11 | our theoretical calculations. Oh by the , there was a clay point |
|
| 56:20 | How do I measure velocity in a ? Yeah, that's really tough. |
|
| 56:25 | got this platelet. You know. I want to eliminate geometric effects. |
|
| 56:32 | I don't have an infinite frequency I could propagate through that wavelet without |
|
| 56:38 | being guided waves or deformation ways in clay platelet, right? Channel |
|
| 56:46 | guided waves. Uh Oscillations of the of vibration of the wave lit I |
|
| 56:54 | of the paper of the platelet. So what that is that's an |
|
| 57:00 | These are aggregates of uh Shelly material in clay but Extrapolated to 100% |
|
| 57:13 | So this was just one point. was something we did in the frio |
|
| 57:18 | in south texas. And that was extrapolate clay point we had there. |
|
| 57:24 | anyway uh the minerals do tend to out right, of course, |
|
| 57:30 | dolomite and clay. What would be like a larger difference in the orientation |
|
| 57:40 | velocity? Would it be in P. Or V. S. |
|
| 57:44 | in B. S. Yeah. . Bs tends to be more dependent |
|
| 57:51 | ndp the if you subtract, if look at Thompson's epsilon parameter which is |
|
| 58:01 | to the difference between vertical and horizontal . Uh It's a lot bigger for |
|
| 58:08 | for share waves than uh Well, is the shear wave difference is a |
|
| 58:14 | bigger than the p wave differences. . Okay, here's some laboratory measurements |
|
| 58:29 | was able to compile and this was clay point we had just extrapolated from |
|
| 58:37 | locality and it's just put there for and now we'll draw a line |
|
| 58:45 | play the calcite which is off, the page off the chart. But |
|
| 58:51 | a line headed in that direction and a line headed from clay the course |
|
| 58:58 | what you see is the points tend get strung out along there. Now |
|
| 59:04 | one problem with laboratory measurements which I've to very briefly. I should have |
|
| 59:11 | more time on it and that is laboratory measurements are biased. How are |
|
| 59:17 | biased? What kind of bias would have in laboratory measurements compared to |
|
| 59:24 | c. two measurements? Mhm. explanation process. Okay well that yeah |
|
| 59:32 | that is a correction fact or a . The rock has been changed and |
|
| 59:37 | usually produces a bias to lower velocities a bigger pressure dependence but there's a |
|
| 59:46 | bias also. In addition so there's bias in the types of rocks I |
|
| 59:52 | sample and make laboratory measurements on. what is that bias? Think about |
|
| 60:09 | process of Corinne and bringing that core the surface in drilling a plug and |
|
| 60:17 | them measurement on that plug. You see a lot of opportunity for |
|
| 60:23 | sample to break or lose cohesion. ? The laboratory measurements that we have |
|
| 60:30 | the literature are for samples that have the process. See what I'm |
|
| 60:39 | We're going to be biased towards more samples. Now in a shell I |
|
| 60:47 | know how much you've handled shells certainly the surface they tend to flake apart |
|
| 60:54 | they? They exfoliate very easily. ? It shells will tend to lose |
|
| 61:00 | cohesion and break very easily. So have a shell survive. The korean |
|
| 61:10 | means that shell has to be well and it could be a court cement |
|
| 61:17 | is fine because the shell has a of course in it already but it |
|
| 61:22 | also be a carbonates in that you line these shells. Mhm. Sometimes |
|
| 61:30 | think we call them morals. Blimey . Um So that means your laboratory |
|
| 61:39 | and shells are going to be biased towards the courts line or the cow |
|
| 61:48 | . So we see things spread out way but we see uh some points |
|
| 61:54 | to approach the calcite line. Other headed towards the courts line. Also |
|
| 62:03 | have dry clays. There will be towards lower p wave velocity. So |
|
| 62:08 | may have problems there if our samples not fully saturated. Um Now there's |
|
| 62:15 | law that says that the relationship has be a straight line. These lines |
|
| 62:20 | just drawn for reference. Who Maybe we have a lower bound which |
|
| 62:23 | a curve there between those points which think we should now I think we |
|
| 62:35 | more time which brings us to the rock line. And if I ever |
|
| 62:40 | you on a test what is the scientific discovery of all time? The |
|
| 62:44 | is the mud rock line were true false. Uh huh. The mud |
|
| 62:49 | line is the greatest scientific discovery of time. The answer is true. |
|
| 62:54 | I'm telling you that right now. the greatest scientific discovery for me personally |
|
| 63:02 | uh the paper I wrote where I up with this line is one of |
|
| 63:07 | most cited papers in geophysics and I guarantee you got me my endowed chair |
|
| 63:13 | the University of Houston. So I very thankful to the mud rock |
|
| 63:17 | I did this as a graduate Why? Because I just happen to |
|
| 63:22 | some of the very early shear wave logs. I did my dissertation working |
|
| 63:31 | digital full waveform sonic logs and processing wave forms and measuring shear wave velocities |
|
| 63:40 | them. Uh And that was so was one of the first people to |
|
| 63:45 | a lot of the shear wave velocity and I was able to notice what |
|
| 63:50 | going on. Uh This particular line combined a lot of different measurements. |
|
| 63:56 | combined These are all in c. measurements. I combined a variety of |
|
| 64:02 | sonic bog measurements. I also included some dSP measurements to get to the |
|
| 64:09 | low velocities in the early days. We didn't have shear wave velocity logs |
|
| 64:15 | slow rocks. Um I even used used some inverted uh surface wave velocities |
|
| 64:23 | uh some uh navy measurements on uh sediments. Um So anyway I plotted |
|
| 64:33 | all up and I just plotted VP . V. S. I happen |
|
| 64:37 | be working part time in a well group and that's what we were |
|
| 64:40 | We were cross flooding logs so why cross flood VP VS. V. |
|
| 64:46 | . And I have been asked, been approached by someone who is working |
|
| 64:50 | a video of all things and he me what should the velocity of Shelby |
|
| 64:58 | the V. P. V. . Ratio of Shelby. And I |
|
| 65:01 | around asking every g emphasised, I the ark a research lab where I |
|
| 65:06 | working part time, what's the P. B. S ratio for |
|
| 65:10 | and they would tell me over Whereas you know, we had pickets |
|
| 65:15 | it was very precise for other pathologies over to sounded like not a very |
|
| 65:21 | number. So um I started collecting measurements and he started to determine for |
|
| 65:30 | what the shale velocities were. And I plotted up shale velocities and I |
|
| 65:35 | spotted Bp roses B. S. I was extremely surprised because what you |
|
| 65:43 | is as you see this very well line. But what you see is |
|
| 65:48 | V. P. B. Ratio is varying continually along the line |
|
| 65:54 | , I've got up here, I a v. p. b. |
|
| 65:56 | . ratio approaching 1.5 down here, V. P. B. |
|
| 66:01 | Ratio. What is that point you know, one point around |
|
| 66:08 | Later on I saw the PBS ratios high as 40, right at the |
|
| 66:13 | bottom. We're using uh ocean bottom and were able to make these |
|
| 66:20 | We had very high Vis PBS duration very shallow. So quite a difference |
|
| 66:27 | the kind of results pick it was Now remember a picket Made his measurements |
|
| 66:33 | the laboratory he was biased towards well the five rocks Here. I'm looking |
|
| 66:38 | in C2 measurements and I'm spanning the range from very poorly, lit defied |
|
| 66:46 | uh pretty relatively well identified for a . So anyway, I put a |
|
| 66:52 | to these points by the way I picked excluded that point because that was |
|
| 66:57 | a near surface measurement on shore In upper 10 ft. And I decided |
|
| 67:05 | that point had to be above the table. So that was partially |
|
| 67:09 | So that actually had gas in the space. It had air in the |
|
| 67:14 | space. Right? So I threw point out for good reason. And |
|
| 67:19 | I got was this line and we're we're getting close to the velocity of |
|
| 67:23 | . In fact, The curve would to bend right. You can't extrapolate |
|
| 67:28 | all the way down. But the here is 1.36. And we have |
|
| 67:33 | very well defined relationship. And I'm sorry to say that nobody saw the |
|
| 67:41 | root of 4/3 here. So nobody the point on there on their uh |
|
| 67:48 | . I don't I don't know if a coincidence or not, but that's |
|
| 67:51 | close to the square four thirds. the minimum possible D. PVS ratio |
|
| 67:58 | have an intercept of zero here And PBS would be square root of |
|
| 68:04 | So funny how that worked out. still haven't figured out the physical significance |
|
| 68:09 | that. That was Both to 40 ago. So then I went around |
|
| 68:21 | I started looking for data in the to support or falsify this idea of |
|
| 68:29 | mud rock line. Now I called mud rocks. His the rocks I |
|
| 68:34 | were not all shell somewhere placed on silt stones. And so these are |
|
| 68:41 | mud rocks. So I didn't I determine that before I try to |
|
| 68:48 | tune this by composition or grain size anything. I'm just going to lump |
|
| 68:53 | all together. I didn't have all many measurements early on. So by |
|
| 68:58 | them all together by calling the mud , I could lump them all |
|
| 69:03 | And the idea here is that these are composed of three constituents primarily |
|
| 69:13 | which is here clay, which is in there and courts which is up |
|
| 69:20 | . Okay, so um all the fall pretty much along this line, |
|
| 69:26 | is probably why you have that straight . Okay. Now, uh even |
|
| 69:34 | I had sonic waveform data in the old days, remember I said in |
|
| 69:38 | laboratory we used to make a silicone well in the logging trucks. Uh |
|
| 69:45 | can actually get in a silla scope of the, of the sonic wave |
|
| 69:51 | . And they could get a camera take a picture of the oscilloscope. |
|
| 69:57 | they could pick the p waves and lay from the silla scope picture or |
|
| 70:02 | could do it. Keep the sonic in place pulse and just measure the |
|
| 70:11 | is manually by looking at the wave and then moving the tool in |
|
| 70:17 | So in the very, very early very primitive. But shear wave velocities |
|
| 70:25 | available and I found this in the logging literature. This is data from |
|
| 70:30 | and I plotted his points. He a table he never crossed, plotted |
|
| 70:34 | never did anything with them, but plotted right on the mud rock |
|
| 70:42 | And then for it picket stand stop which was a big surprise remember his |
|
| 70:51 | . P. B. S ratios from less than 1.6 to more than |
|
| 70:56 | . And in fact the sandstone data following the mud rock line. And |
|
| 71:03 | was a huge surprise that shells and with the same velocity have very similar |
|
| 71:12 | pds rations by the way, keep mind these are all brine saturated |
|
| 71:17 | right things will be different when we hydrocarbons to the sands. But for |
|
| 71:23 | saturated sands, pickets, laboratory motions right on the mud rock line. |
|
| 71:31 | I'll leave you with that. And let you chew on that idea, |
|
| 71:37 | if sand stones and shells flawed on mud rock line, that means most |
|
| 71:43 | the rocks in the gulf of Mexico the gulf coast that don't have um |
|
| 71:52 | in them have the same V. . B. S. Relationship. |
|
| 71:57 | see the power of that. If alter your V. P. |
|
| 72:02 | S. Relationship now we have a to distinguish hydrocarbon bearing rocks from all |
|
| 72:09 | the rocks. They will. The barren barren rocks will fought off the |
|
| 72:15 | rock line whereas the brian sands and etcetera, silt stones will all plot |
|
| 72:22 | the mud rock line. So anyway is where we are looking at tickets |
|
| 72:28 | as we collect more data and we what's happening better. Will realize that |
|
| 72:36 | data set is a very specific data and that sands may plot on the |
|
| 72:42 | rock. One line brian sands depending their composition. They make club and |
|
| 72:48 | , they may plot slightly below or they plot slightly above. So we'll |
|
| 72:54 | more of these VPs ratios. Next questions okay I'll stop |
|
