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GEOL6350-Advanced Structural Geology - Day2 PM 02-19-2022
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00:00 and then go ahead and get And what we're going to do next
00:06 take the things that we've learned about mechanics and fracture mechanics and apply them
00:12 top seal failure. And first I to review some of the things that
00:25 talked about um in this block what what kind of fault are we
00:30 at? Normal? No fault. . With this side being footballer hanging
00:54 footfall going up here, hanging all . Good, perfect. And then
01:04 talked about this that the the fault thickness varies as a function of
01:11 It's not just a single line. actually has some fire with. And
01:16 can use that to estimate fault displacement from the thickness of the fault zone
01:23 we see in core. And then talked about the conservation of throw.
01:34 throw around these intersections needs to add to be consistent. So that if
01:40 have 200 ft here, You would to have 100 ft there and 100
01:46 there. That the sum of these has to equal the total of
01:52 And depending on how the faults come here and here we have synthetic false
02:00 and here we have anesthetic fault. so you would if you go around
02:08 a different way, you would go 150 plus this 50 equals this 200
02:14 here. Mm hmm. And so all our fault fault intersections that some
02:19 the throws has to be consistent. that can help us decide if we
02:25 the right event in some of these fault blocks when we do the sizing
02:38 . And then for the fractures. What? Mm hmm. Here we're
02:46 at joints. What are we what we looking at here fractures?
02:57 Beef bed parallel fractures? Yeah. here where we have these multiple sets
03:03 joints, um which what do we this one? And what do we
03:10 this one on A E. One, Y B E.
03:22 Two. Yeah, Perfect. And then along the joint surfaces like
03:29 , we see these promos features um indicate the direction of propagation of the
03:38 as it grows. So it grows following all these lines on the playlist
03:47 . Okay. And then we talked this that both the natural fractures and
03:54 fractures propagate parallel to Sigma one or H. Max. And so from
04:02 orientation of induced fractures or natural fractures this, we can infer what the
04:09 of signage max and signage men are what the optimum? Well, as
04:17 myth is for staging hydro fractures that want to be parallel two sigma three
04:23 get the most effective hydraulic fractures opening to sigma. H max sort of
04:31 parallel to signage from when the fracture to sigma h max. That's true
04:37 both natural fractures and hydraulic fractures. , so we'll go on now and
04:46 about top seal failure. We'll take things that we learned from two mechanics
04:51 apply them to the particular case of failure. Mhm. So here's here's
05:00 outline of what we're going to talk that. There are two top seal
05:05 mechanisms, capital reenter pressure and mechanical failure. This mechanical top seal failure
05:12 a natural hydraulic fracturing capillary entry pressure where the buoyancy pressure of the hydrocarbons
05:20 high enough that it can enter the space in the top seal. Mm
05:25 . Then we'll talk about the definition causes of fluid overpressure the fluid pressure
05:33 . And we'll spend a lot of talking about pressure depth plots and do
05:37 exercises along that. Hm. And we'll look at indications of mechanical top
05:43 failure where you see seats and things are indicative of topsail failure in your
05:51 trap. Ah We'll do some pressure exercises and then we'll look at some
05:58 of top seal limitations due to fluid or hydrocarbon column. Mhm. And
06:05 of the important points is that traps at autopsy of failure can still
06:10 hydrocarbons. And we'll look at a of examples of that. So if
06:17 total fluid pressure in the hydrocarbon column the topsail capacity. You can still
06:25 some hydrocarbons and it's kind of a equilibrium and then we'll talk about pressure
06:32 traps and um false seal failure that , critically stressed, false conceal and
06:41 is contrary to conventional industry wisdom. we'll look at some examples of ceiling
06:48 stressed false and then we'll do an with conversion factors from pressure depth
06:59 Okay, so schematic cross section of trap here um with our dip closure
07:09 , total column height from the crest to the spill point here. Total
07:15 depends on the dip closure and the dependent closure and what we're going to
07:20 talking about. And how are the seal failure mechanisms? Um Top seal
07:27 be limited by the capital's central pressure by mechanical fracture strength of the top
07:33 and the hydrocarbon buoyancy and fluid pressure the Minimum horizontal stress and cause hydraulic
07:41 there at the top two. So are the two potential limitations on our
07:46 capacity. Okay, so mechanical failure when the fluid pressure all right moves
08:02 stress circle to the left and intersects failure envelope. Either in shear fracture
08:08 tensile fracture mechanism here and this opens . Um This opens up joints or
08:15 fractures that then can allow the fluid escape. And so the ah one
08:29 the things we have to address is what is more likely to cause
08:33 What causes failure? 1st catholic central or hydraulic failure. So we talked
08:40 hydraulic failure as one of that fluid reduces your effective normal stress to a
08:46 value. Capt. Lory failure occurs the buoyancy pressure on showing a
08:54 you're of a couple of sand grains spacing between the sand grains by the
09:00 here, water here the reservoirs are water wet. And so capillary failure
09:11 when the buoyancy pressure of the hydrocarbons great enough to displace the water in
09:17 pore throats of of the topsail. this has, becomes a function of
09:24 buoyancy pressure. The inter facial which is a function of whether it's
09:29 or oil and the poor throat Alright, so this um we talked
09:44 this. The displacement pressure is proportional the inter facial tension, the cosign
09:52 this wedding angle and inversely proportional to poor throat radius. The so here's
10:01 we measured captain range of pressure. take a core plug like this and
10:07 it in a centrifuge like this which typically filled with mercury. And then
10:15 we spin that around to increase the on it until the mercury starts to
10:22 the pore space in the rock in core sample and record, we record
10:29 as mom, a series of crafts this where you're looking at the wedding
10:37 saturation. So this is the um is the the saturation of the water
10:46 the pore space as you spin this in the centrifuge and increase the
10:54 The pressure goes up following in line this until it starts to displace the
10:59 in the pore throats and then it over like this and um and continues
11:06 increase along a trajectory like this. inflection points represent the calculus reentry
11:14 Um In terms of mercury air caterpillar pressure for that particular sample. So
11:22 measure these things with mercury air Capital pressure and then we have to convert
11:28 two the Capital Metro pressures for Okay so this is a this is
11:38 history graham. Now. Different different of top seal here versus the mercury
11:46 capture Antrel pressure and the black bars are all deepwater gulf of Mexico shelter
11:55 and shales. Um The average capital pressure of all these samples is about
12:04 p. s. i. So tells us the mercury air calculate central
12:10 . You need to convert that to and gas capillary entry pressure. That's
12:25 . Okay so there are two steps want to do here. First we
12:28 to convert the mercury air capital of pressure to oil and gas, Capital
12:33 pressure and then convert those capital reentry to buoyancy pressures and column feet of
12:41 and gas. So that way we relate the topsail capacity to the hydrocarbon
12:48 that we have trapped below that Alright so this is a this is
13:01 nom a graph for converting that mercury catholic central pressure to oil and gas
13:07 central pressure. Okay and basically you at the measure capital to enter
13:16 Mhm. Yeah you look at the and pressure along here and extrapolate up
13:28 this line. Um to get the facial tension to calculate the oil and
13:35 capillary entry pressure. And this This from A reference in old paper in
13:47 paper by Showalter and I've added to a number of references that include all
13:54 information. So if you want to up on some of this, you
13:57 go into it in more detail from references. So if we if we
14:08 those conversions of mercury capital entra pressure oil and gas, capital entra
14:15 we get these hissed a grams where average shale capital under pressure for oil
14:23 about 300 sigh. Yeah. And average capital intra pressure for gas,
14:31 higher. It's about 1140. so the same rock can hold different
14:40 pressures. Then gas pressure is the rock can hold twice as much gas
14:45 and as oil pressure. And this this is this is counterintuitive because the
14:53 is actually lighter, mm hmm. because of the inter facial tension,
14:59 same rock can hold a greater gas and the buoyancy pressure. Okay,
15:11 we want to convert we want to these buoyancy pressures to column height,
15:18 is something we can measure directly in in our maps and cross sections.
15:25 to do that, we need to these these equations and what we're trying
15:34 taking this pressure difference and calculating the white, it corresponds to that pressure
15:43 . So for Yeah, for oil gas, this DELTA P equals the
15:52 height times the density of the water the density of the oil to get
15:59 oil column height. And for gas DELTA P equals the density of the
16:06 minus the density of gas to give the column height in gas to combine
16:11 feet for gas. So, if just invert this to sulfur, H
16:16 get these two equations and um solving for capillary entry pressure, the column
16:26 for oil Equals the capillary entry pressure oil. So the 300 c.
16:33 divided by 0.45 minus 0.3 C per to get the column height of oil
16:40 feet. Mhm. The top seal hold analogs loose the analogous leaf.
16:46 gas we saw for the gas column by dividing the capital intra pressure for
16:52 gas by um the density of the minus the density of gas to get
16:59 gas column height in feet that the seal can hold. Alright,
17:13 um assuming these values for water oil density and gas density, when
17:21 convert those buoyancy pressures to column we get these hissed a grams that
17:27 that the average max returnable oil column for shale is about 20 100 ft
17:33 oil, mm hmm. And it's to about 30 800 ft of
17:39 True. And as I mentioned, is this is counterintuitive because the gas
17:44 lighter to the oil. But the inter facial tension is greater than the
17:52 into facial tension. So the same has a much higher capital entra pressure
17:58 gas. And I think those for . Thanks. So even though the
18:04 is lighter is more buoyant, we retain a greater gas column white than
18:10 then an oil column point. And to most of our traps must the
18:22 height of total closure height of most our traps. These are pretty large
18:28 . You you'd be lucky you're lucky find a trap that can hold 20
18:34 ft of of Closure or even 30 ft of closure. You can even
18:39 fortunate. Okay, okay. So I want to emphasize these ideas about
18:49 your disclosure and calm, right? , given this, given the sketch
18:55 , what is the total possible Mm hmm. 100 ft on what
19:26 did was I wait 700 ft. from the crest, 1 5000 to
19:34 oil water contact. 1 5 Well, that's the that's the total
19:43 column height, but the total closure actually greater. Goes from the crest
19:50 the way down to this. Still here at about Um 15,900.
19:59 Okay. Yeah, yeah. So important to understand this difference So that
20:08 total closure goes from the crest 1500 and 14,900 all the way down
20:15 the spill points, we have about ft of total possible closure. The
20:22 height. You calculated correctly from the here, down to this oil water
20:31 . So that's That's 700 or 800 depending on. But what you choose
20:36 from the crest in the difference indicates the trap is actually under filled relative
20:44 the total closure. But we could another 100 or 200 ft of columbine
20:51 here. Um, if we're going fill it up to this total still
20:57 , Okay, Now this gets this more complicated from that, from that
21:05 column height, we want to know is the buoyancy pressure of that
21:11 At the trust of the crest of trap? Right. To do
21:15 we assume these average density gradients of micro foot for water. 10.3 per
21:26 for oil. All right. And to calculate that point, see
21:42 We take that 800 ft call him and multiply at times the difference in
21:50 two density gradients. .455 -33 together the pressure for an oil column of
21:59 124 c. Now, with that ft calm height and 124 points the
22:12 . What's the what's the risk of failure? How does this compare to
22:16 history grams that we just looked at top seals. For oil buoyancy
22:28 It should be pretty low. Pretty , Yeah. So, if I
22:32 at this history graham for top the average Of these retain herbal capital
22:38 intra pressures is 20 100 ft. so borrow What do we have?
22:46 ft 10 24 p. s. . So that's that's pretty low compared
22:55 the points he pressured required to equal the top seed capital central pressure.
23:05 , okay. And that's that's shown , where the points of pressure is
23:11 124 C for this column? And the average topsail capacity for oil
23:17 about 300 c. So, we're little less than half of the average
23:26 capital central pressure for oil. good risk of feeling about Captain Andrew
23:31 is very low as Angela smith. . Alright, so that's capillary
23:43 Now, we're going to talk about top seal failure or natural hydrofracking.
23:47 right. And what we're what we're to here, what we mean by
23:56 topsail capacity is the poor pressure that the mechanical steel capacity, um causing
24:06 causing hydraulic fracturing of the top sale . So what is the poor pressure
24:12 required to drive that stress circle to right? To intersect the failure,
24:19 ? To the left, intersected And this is this is also referred
24:23 as topsy leica breached trap or a seal or a brown trap blown
24:31 And it happens when that poor pressure greater than the minimum horizontal stress.
24:43 , so what is what is over on? And I'm showing that here
24:47 this schematic the pressure dump diagram, water line would follow just a straight
24:56 like this representing just the weight of water column. So at any point
25:02 z here, the weight of the column would be some. It's relatively
25:08 pressure like this. Overpressure refers to the shift of that fluid pressure to
25:17 right, the magnitude of that shift the right. Mhm. So insert
25:23 total fluid pressure in this part of section equals the hydrostatic pressure plus the
25:33 . And this overpressure develops went typically over compassion when mm hmm. The
25:45 are deposited so rapidly with low permeability part of the weight of the
25:52 the load of the sentiments is transferred the rock matrix to the interstitial
26:03 Okay, there are multiple potential causes overpressure. This disequilibrium compaction that I
26:10 described from the rapid burial of impermeable is the most common. Um But
26:18 can also be generated by tectonic compression a roofing. And look at a
26:25 of examples of that. It can be caused by hydrocarbon generation. Aqua
26:33 expansion. So just the expansion of water duty heating up in the mineral
26:39 and mineral transformation reactions with. As increase heat in pressure, we transformed
26:48 clays and drive water dehydrate to clay's you drive water out of the clay
26:54 that contributes to over partnership then contributes overpressure generation. Mhm. You can
27:04 get over pressures from lateral transfer or transfer. Hydrocarbon pliancy pressure that will
27:13 about a lot. And in lateral transfer is an important mechanism where
27:22 , mm hmm two water gradient line the 00 point at a higher
27:31 Then then you're in your area of and we'll look at some examples of
27:45 . Okay, so the most common of open pressure is that this equilibrium
27:50 . And here I've got depth versus , grasp in depth versus ferocity.
27:58 the fluid can escape, the food follows this blue line is a function
28:03 debt. Mhm. The porosity follows blue line where the porosity continues to
28:12 with with increasing depth, you get over pressures when the ferocity doesn't decrease
28:23 with with increasing stress. So you're approaching kind of a no A minimum
28:31 of ferocity. That's non zero here this case about 20%. So when
28:37 bury these things rapidly to prosperity, fluids can escape across city doesn't decrease
28:45 overpressure develops within those workspaces and then weight of the rock column now is
28:52 by the poor pressure in addition to rock itself. Alright. And here
29:02 got two seismic sections. Their views the same seismic sections. So here's
29:09 typical from reflectivity section. And here have extracted the velocities for that
29:19 Mhm. Because the velocity is a of the compaction state, the ferocity
29:25 effective stress we can use the velocity calculate for pressure. Mhm. And
29:32 here, for example, here are the blue are slow velocities. The
29:38 are high velocities. They're shown by scale here as I go deeper here
29:45 my philosophies continue to Okay. In philosophies continued to increase and my fluid
29:57 is following basically a normal gradient here in this area. I have lower
30:04 expected velocities indicating that I have over . So when we have some actual
30:11 points, like any one of these , we can calibrate that relationship between
30:18 and overpressure and then use the velocities estimate what the over pressures are
30:24 In the unexplored sections of the Okay, so typically we have a
30:38 of different ways that we measure fluid besides velocities and one of the one
30:46 the most commonest mud weights. Because have a lot of mud weight data
30:53 and I'm shown here a pressure depth with a with a static gradient
30:59 the hydrostatic radiant here in the blue then individual mud waits shown here in
31:06 in all the circles, the whole whole reason for using mud in the
31:11 is to keep fluid from flowing into wellbore and housing a blowout. So
31:18 the mud way tree typically slightly greater the fluid pressure. So in this
31:25 case the fluid pressure is probably somewhere the bottom of this scattered data cloud
31:34 these mud ways are higher. Then actual poor fluid pressure in order to
31:41 that poor fluid pressure in the rock to keep it from flowing into the
31:45 and gust to blow up. Excuse . So this is one way we
31:52 can estimate fluid pressure. The other is from trail stamped, cast in
32:02 information, repeat formation, modular test a in a trial stand test shown
32:10 a schematic here where we're looking at world war, here's the rock,
32:15 here's the will board. Um Here's our modern line gauge. We insert
32:24 packer to close off the section that want to test and then open
32:31 open the valve here and let fluid the rock flow into the, into
32:37 drills, Manchester and then close, allow that pressure to stabilize, close
32:43 valve and record that pressure. And that gives us a direct measurement of
32:49 formation pressure in that interval of the door. We also have these
33:04 more sophisticated tools called R. T. S. A repeat formation
33:09 , a modular dynamic formation tester and and this is a slim bridge trademark
33:16 and then a formation multi tester which a mm hmm a general industry term
33:23 this type of tool. And what do is lower the tool on a
33:30 hmm. Lower the two on wire . So insert the probe into
33:38 into the mm hmm. You know borehole, allow the formation pressure to
33:46 up in this tool and collect a and measure the pressure of that
33:53 And this is this is nice because allows us to collect a sample as
33:58 as measures the pressure. So we if the pore space here is filled
34:03 water, oil or gas. Leadoff tests are another way to measure
34:17 the formation pressure and this is a of leak off test where this is
34:24 the volume or time versus versus And this is the pressure that's recorded
34:31 the on at the casing at the of the casing string. And typically
34:41 do this to make sure that mm . We have sufficient mud weight to
34:47 ahead without fracking the rock. Um anywhere a leak point anywhere along this
34:58 part of the curve is referred to a limit test or information integrity
35:05 If we allow the pressure to go to where it starts to go through
35:10 inflection. This inflection is measured as leak off pressure for the fresher opening
35:19 and this represents the pressure where the weight is actually starting to fracture the
35:25 and cause fractures to propagate away from world war. If we continue to
35:32 the pressure, the fraction will begin propagate rapidly to have unstable fracture
35:41 And now the fluid pressure is going drop again as those fractures open and
35:47 grow. And then at this point U. F. P. Is
35:52 ultimate fracture point or unstable fracture propagation . Mhm. And then if we
36:02 in the tool the pressure will drop we'll get these fractured closure pressures where
36:11 well is shut in now and the can close and reduce the pressure in
36:17 in in the subway car. And these these leak off pressures or information
36:29 fracture pressures. This point are most recorded as a Sigma three or our
36:35 age men. Um So here's an of a pressure depth thought pressure
36:51 depth here, for reference Lucas static here, about one cm per foot
36:59 gradient here about 0.45 P. I. Crow foot and all the
37:06 of leak off test data. The is here with each one of these
37:10 points representing an individual leak off So each one of these points
37:20 I quite like that in a week test friends. And then True,
37:27 of this cloud that represents the most estimate of the fracture gradient or the
37:36 horizontal stress. So, we can these leak off tests to estimate what
37:44 fracture grading of the minimum horizontal stress a function of depth. Ah So
37:58 there we got two things to this over pressured water pressure line here that
38:07 to the right from this hydrostatic So this represents my overpressure and a
38:14 pressure gradient here. Um Starting from free water level, the oil water
38:22 at a gas water contact migrating up that lower density for the hydrocarbons with
38:29 or gas. And when this hydrocarbon reaches the fracture gradient is when we
38:39 to open fractures in the top seal get mechanical topsail failure. Okay,
38:51 the top seal failure or natural hydrofracking when the fluid pressure gradients intersect the
38:58 gradient. And that could happen either , shallow or the water gradient intersects
39:04 leak off test cloud or intersects the gradient, I should say. Or
39:09 can happen deeper in the section where hydrocarbon pressure gradient intersects the um In
39:15 sense, the fracture gradient. And when this occurs, oh,
39:24 reached a sort of a dynamic The track can still hold this hydrocarbon
39:30 fight, but it can't hold So if more hydrocarbons bubbling in this
39:37 , hydrocarbons are going to bubble out top through the hydro fractures in the
39:41 of the track. So even though in hydraulic failure, we can still
39:46 hydrocarbons in this trap. Mhm. now that the the bottom of this
40:00 off. Test cloud this fresh You can see it's not exactly
40:05 It's kind of curvilinear increasing towards the gradient with increasing pressure and increasing
40:14 And that's that's an artifact of the mechanics. It has nothing to do
40:19 with the tectonic environment. So here got 1, 2, 3,
40:24 different basins. All of them are along normal faults settings. But we
40:32 that that the bottom of the league test cloud, that minimum horizontal stress
40:39 is curvilinear. It starts to curve towards the little static gradient with increasing
40:45 with increasing pressure and depth. We'll you in this space in you
40:50 we see it again in this space here. We see it again in
40:56 basin where we have just the leak test portrayed. And here we see
41:01 in the space and number four. we see it here Turning over in
41:07 of these two. It's nice. fracture gradient. It's nicely dividing the
41:14 off test data here from the measured pressure data here. So, this
41:21 gives us a good estimate. I minimum horizontal stress and the maximum fluid
41:27 that we could retain along this Mhm. Alright. So here are
41:38 indications of warning signs of mechanical topsy failure. Um something like this where
41:45 see but mud volcanoes, month mounds the along the sea floor. Mm
41:53 . Something like this where we have synthetic seeps growing along the sea floor
41:58 they're feeding on the oil that's coming through the top seal. Mhm.
42:04 see it in seismic vertical profiles with zones like this, often with a
42:11 volcano where we'll see at the sea at the top of that. I
42:15 so. So all these things are the underlying trap being at top seal
42:29 . Here's some other examples. This another seismic wipe out zone, a
42:34 sizing zone with a crater here at sea floor. Mhm. Here's the
42:41 C format alarm the surface. And see the event here with fall scarves
42:50 and here due to slumping from the coming up. This this feature pock
42:56 here at the bottom from fluid coming along along this zone. So,
43:03 you see these things in the seismic , that's an indication that you're trapped
43:07 everybody is down here is the autopsy film. Here's another example here is
43:18 , but sea floor bottom map again a scarf here, vents all along
43:24 looking sort of like a moon created . Um On one volcano here with
43:31 slumping off there. And all of features are indicates indicators of high fluid
43:38 in the underlying trap. This is example from the black sea where you
43:46 a big mud volcano at the sea here with a wipe out stone
43:52 Both of these features indicating that somewhere depth under here, there's a trap
43:58 a topsy of failure. Um now, as I mentioned when these
44:11 failed due to the hydrocarbon pressure reaching fracture gradient, they can still retain
44:19 . So this is a pressure depth for the trap that underlies these chemo
44:25 seeps. So the seats are telling that the track is that failure
44:30 The hydrocarbon pressure equals the fracture gradient fluids are escaping out to generate these
44:38 to result in these seeds. But you look at the pressure death
44:43 we see that even though the top the oil pressure column line here intersects
44:48 fracture gradient, but we're still retaining a 1500 ft oil column. So
44:55 is at the maximum topsail capacity. time a bubble of hydrocarbon comes in
45:01 bubble of hydro currents has to escape the top. Um but It's kind
45:06 a dynamic equilibrium where we still maintain column height of about 1500 ft.
45:14 hmm. This is another example. is from a A faulted four way
45:21 . This is the oil, the column here, shown in the red
45:28 the black or the contours um Blue where it's water wet red shows where
45:35 harder hydrocarbon spills oil theory and these the individual faults that cut through
45:43 This is the pressure depth graph for trial. Mhm. You see depth
45:50 versus pressure here. These circles represent week off test data. So that's
45:57 that's my fracture gradient. The green here and here represent oil pressure measurements
46:05 this oil column. And you see oil columns measurements go right up and
46:11 the fracture gradient. But we're still 1000 ft of oil column in this
46:17 . So again it's a dynamic equilibrium oil is escaping out the top,
46:22 we're still retaining A large column in case 1000 ft oil column.
46:32 Okay. Here's some natural examples of and geysers. Hello, these three
46:40 from southern Utah where there are a of C. 02 filled traps and
46:46 mentioned earlier that everything we talked about here refers to both CO two sequestration
46:51 oil and gas retention. And this an example where top so failure is
46:57 the amount of co two in these here where there's been a well bore
47:03 into it. You have a geyser Co. two and water emanating along
47:08 same fault zone elsewhere. It reaches surface. You have these seats of
47:18 . Two rich water for me calcite forming calcite and water along the fault
47:26 . Where this where the fault zone trapping the C. 02 goes under
47:31 green river, you actually get gas coming up into the into the river
47:36 where it goes across the false Um Mhm. The area around
47:49 A. Is just rife with natural seeps. The la brea tar pits
47:56 , for example of a natural oil where the there's an underlying trap that's
48:01 topsail failure and hydrocarbons are migrating up the surface. Um This is an
48:09 of seeps along the santa barbara And then again, this is where
48:15 are autopsy of failure and oil is through the hydro fractures up to the
48:21 surface. Mhm. And this is interesting example because in this case,
48:27 from offshore platforms, reduce the reservoir and actually reduced the seeps. And
48:37 here's going into more detail on Here's the, the santa barbara Channel
48:44 . Here's the coastline here. The outline here is this south Ellwood field
48:52 the red spots on here, or there are seats on the sea
48:58 Now, as a, as a of developing and producing this field,
49:05 operator are going this place was required place heap tense over some of these
49:12 to monitor the seat, which as produced the field to make sure they
49:17 causing more seats And what they found just the opposite that as they
49:25 they actually reduced the seed thought. here's a here's the craft of volume
49:33 gas per day trapped in those in tents. So that's what's trapped in
49:40 tents that they placed over these seeps you see that mm hmm. Thank
49:49 . Comes along at a fairly constant . There was some monkey business with
49:53 seat tent here that they had to for so they get this extrapolated line
50:00 extending through here And then starting in , the seepage started to decrease dramatically
50:09 this inset here is a graph of for pressure as a function of
50:17 And what you see is that as that restaurant pressure started to decrease About
50:25 in 1984. I mean by decrease significantly below hydrostatic Yeah. What
50:36 is that pressure, decrease the seat ? The natural seat which also naturally
50:44 . So in this case the the rather than causing more pollution, actually
50:51 oil seeps into the water around santa . And so I put this insight
51:01 show that as we, as we the pressure here, if we represent
51:08 in pressure, death space, we this oil gradient line away from the
51:13 gradient and reduce the conditions causing hydro and seat they chucked through the up
51:19 the fracture gradient here. Okay, hmm. Alright. So this was
51:28 of the, one of the exercises I gave you and I want you
51:32 take a minute and do this. And you can do it in power
51:36 on your screen or you can do estimated on my screen or do
51:42 You can sketch it on the power that I sent you. What I
51:48 you to do is draw a hydrostatic gradient, show an increase information pressure
51:55 the seal bed. So this is is the seal bed here? This
52:00 the sea floor or mud line, sea level is here at the top
52:05 the graph. And then um I you to add a minimum horizontal stress
52:19 considering you're in a normal fall of . All setting one. Oh and
52:25 label that below the seabed, mm . Assume that the formation pressures hydrostatic
52:32 this part of the section And that minimum horizontal stress gradient. Oh,
52:38 the minimum horizontal stress gradient is also fraction purity. So, draw 100
52:43 water gradient. An over pressure gradient the seal bed. And overburdened gradient
52:50 gradient. And then a minimum horizontal gradient. Mhm. Mhm.
52:57 take take a few minutes and let know when you've well, when you
53:01 this. So, how's everybody You had a chance to work through
64:40 . Yeah, I see lots of head now. It's okay. So
64:45 let's talk it through. All so, the the hydrostatic water gradient
64:54 be just a linear gradient starting from origin here at sea level extending down
65:01 the bottom of the section in one straight line. Thanks, the over
65:10 gradient is going to be shifted to right of that hydrostatic line. The
65:16 of the over pressure gradient will be to that hydrostatic gradient. Mhm.
65:23 through the seal bed here, you'd some kind of linear or curvilinear line
65:29 the hydrostatic gradient at the top. the over pressure gradient at the
65:38 Mm hmm. Are you all with so far to go look?
65:45 Okay, good. And then the static gradient needs to start from the
65:59 line and go somewhere off to the like this. So now it's representing
66:05 weight of everything overlying it. So representing the weight of the water column
66:12 the weight of the mud column at mud line. It's the same as
66:16 hydrostatic radiant. They both represent the of the water car. But then
66:22 you add sediments and go deeper, starts to go off to the right
66:25 this. And lastly, the minimum stress gradient Should be about 60 year
66:36 70% of the overburden gradient. Again from the mud line and following a
66:43 like this somewhere to the left of electrostatic gradient like that. Any questions
66:54 comments on that so far is Always gonna be 60 to 70
67:07 No, no, it's not. Remember as we go, as we
67:12 deeper to higher pressures, it gets to the low hispanic line. So
67:18 starts out in the shallow section is 60-70%. But once you start to
67:24 the overburden it gets closer and closer becomes curved And up in approaches 90%
67:32 the electrostatic gradient. So it gets close to the little static radiant as
67:37 get deeper mm hmm. And in we usually approximated as a linear function
67:49 because it makes it easier to do . It's the lazy man's approach,
67:59 . Any other questions or comments with ? Mhm. And this this is
68:07 important thing to make sure that the in the minimum horizontal stress start out
68:13 that point at the mud line and the last part labeled the minimum horizontal
68:33 stress above and below the seal So here we're looking for the difference
68:41 of the minimum horizontal stress and the pressure. So we'll have two lines
68:50 here. One up here between the horizontal stress and the food pressure
68:57 which is hydrostatic. And then here the minimum horizontal stress and the over
69:04 . Online fun. And you can that as that overpressure line moves to
69:10 right. Is that over pressure That effect is tres gets smaller and
69:27 . Okay. Is everybody good with ? Because it's important to get these
69:31 of what we're gonna do next? . Let's see. We've been we've
69:36 going about an hour. Do you to take a break or do you
69:39 to go plow ahead? Take a . Take a break. Okay,
69:46 . It's a 10 minute break. back about five minutes off.
69:54 Thanks. Thanks for sticking with me coming back. Okay, so,
70:02 now we're gonna talk about how that in fluid pressure that we just sketched
70:07 hydraulic fracturing. And again, here's friendly, more cool and diagram showing
70:15 as you increase the fluid pressure, move those circles to the right until
70:21 intersect the failure envelope, particularly in tensile mode here. And that's when
70:27 generate these heightened national hydraulic fractures. , mm hmm. Okay, so
70:37 we're gonna relate these pressure depth profiles hydrocarbon accumulations away. So here we
70:46 the hydrostatic pregnant and oil gradient here and a fracture gradient here. Um
70:54 oil gradient here corresponds to this oil here in the cross section.
71:05 if I move that oil gradient or over pressure gradient far enough to the
71:11 to intersect the fracture gradient, then poor pressure equals the minimum horizontal
71:17 And I start to open natural hydraulic and leak off fluids from the reservoir
71:23 here. No, there's a series animations to show that. So there's
71:34 a small oil column, small oil there in my trap. Still large
71:40 stress between the oil gradient and the gradient as I increase that oil
71:52 that oil pressure gradient moves to the , the oil water contact moves down
72:00 trap fills up here and I start reduce the effect of stress between the
72:06 column at the crest of the trap the fracture gradient. Okay,
72:14 now, at this point my oil intersects the fracture gradient and I start
72:20 generate natural hydro fractures in the crest and cause fluids to leak off through
72:26 crest at this point. So now additional hydrocarbons can be added to the
72:37 . Any additional charge that comes in going to cause an equal volume to
72:43 out the crust of the trap. so the column height here and here
72:49 in a dynamic equilibrium with the fracture pressures. Sorry, All right
73:00 what we're going to do now is the aquifer gradient, the water pressure
73:07 here. So here everything is Now, I've applied a small amount
73:14 overpressure here and my trap is still to the spill point here. At
73:23 point I've increased my aquifer gradient I've increased the overpressure in war.
73:31 hydrocarbon gradient intersects the french gradient and I'm at the maximum mechanical topsail
73:42 So now the topsail capacity, it's to limit how much hydrocarbons I can
73:47 in there as I continue to increase overpressure further, I'm pinned at this
73:56 at the crest of the trap. so the oil water contact has to
74:01 up and the hydrocarbon column is trapped there becomes smaller. My column height
74:08 now limited by the mechanical seal capacity the overpressure. At this point
74:18 hydrocarbon gradient equals the fracture great or water gradient. My over pressure gradient
74:25 equals a fracture gradient. There is effective stress space space to put any
74:31 in there and my trap is completely it. The water pressure is completely
74:38 the mechanical seal capacity. And I put any more hydrocarbons in there.
74:47 as I as I increase that fluid , I reduced the amount of hydrocarbons
74:53 could fit in that trap until eventually all gone. I can't fit any
74:57 hydrocarbons in that trap. Okay, , so now we have a couple
75:06 these couple of examples. I want look at where the crest of the
75:10 . Is that the maximum top steel , but we're still retaining hydrocarbons.
75:17 This comes from the sheer waterfield in central North sea. Mm hmm.
75:26 reservoir is shown here in the upper and in pressure death space, there's
75:35 fracture gradient, there's my hydrocarbon there's my over pressured aquifer gradient.
75:42 so based on the pressures. This right at the topsail capacity, but
75:49 still retaining 12 3000 feet of Despite being at the week off point
75:59 and again, this is the dynamic where any more charge that comes in
76:03 to be compensated by a charge being at the top. Okay, now
76:15 want to talk about what we call traps and these are traps that are
76:20 to a weak point. So, definition of protected trap is one that's
76:25 to a weak point and that's shown cross section on the right here,
76:30 I have a higher combination here. secondary culmination here, that's retaining oil
76:39 , mm hmm. The pore pressure modulated by the crest of the trap
76:46 . Where at this point the pore equals the fracture gradient in pressure.
76:50 space. That's at this point So my over pressure gradient equals my
76:56 gradient. But as I go deeper into the section, as I go
77:02 into the reservoir, I have more stress space here between the overpressure and
77:08 minimum horizontal gradient that I can start put in some hydrocarbons in here.
77:14 this is what we call a protected where the oil in this accumulation is
77:19 from top seal failure by this higher that allows the reservoir pressure to leak
77:25 and modulate the reservoir pressure. And is an example from the gulf of
77:35 . This is from the mars field the gulf of Mexico. You see
77:40 the mars fields over here with two sands, the scarlet and the pink
77:45 here, and these are over But if they if I follow that
77:52 , those reservoirs up to this You see, I've got a leak
77:58 point here, I've gotta wipe out in the seismic in this point,
78:03 modulates the water pressure in those two . So as I go back down
78:10 over the MArs field, I come here and I have effective stress space
78:15 I can begin to retain calm hydrocarbons the fracture gradient and the aquifer
78:26 Um And this this gets to the that often it's it's better to explore
78:36 subregional high point than the actual apex . We're looking at a series of
78:43 in a toe thrust fold where I the highest point here and then secondary
78:50 is here and here and here and here while separated by these saddles from
78:57 point. So um we were seeing this kind of scenario. Long
79:06 We're at that apex. I can the water pressure and retain effective stress
79:14 deeper in the cards and maintain traps strike in there so that the high
79:24 can't retain any hydrocarbons. But that's create protected traps in these other combinations
79:32 there's enough effective stress between the water off this point and the effect of
79:38 gradient to maintain an oil column in other secondary structures. Mhm.
79:50 so I gave you this as an . Um I have a a schematic
79:57 section here and a pressure depth schematic here. What I want you to
80:04 is on the pressure depth diagram, a aesthetic gradient in a fracture gradient
80:12 then draw a reservoir of water pressure , assuming the waterline hits the fracture
80:19 at this crest, warn. And between these two red lines draw a
80:27 pressure gradient um to represent the pressure the trap here and then we'll talk
80:35 if the hydrocarbon gradient hits the fracture in the diagram will the hydrocarbons only
80:41 . Mhm. So you have this that it's a handout or as a
80:45 point? Um Take a few minutes draw the these gradients that have asked
80:52 try and just let me know when when you've completed the exercise and we'll
81:01 about it. Excuse me, Um The reservoir. What's up
81:56 Is it the overpressure line? It it will be an overpressure line.
88:15 . Okay. Should we go ahead talk this one through? Yes,
88:26 . All right. So you're the static gradient and the fragile gradient should
88:31 something like this. More or less slope in the position are not really
88:37 . You just what's critical is that electrostatic gradient is to the right of
88:42 fracture gradient, and the fracture gradient he is close to the pressure
88:48 but somewhere to the left of Now, the reservoir water gradient is
88:57 more constrained than that. So, we've defined this as a protected
89:03 that water gradient needs to take off the fracture gradient right here at this
89:11 in the exact slope. It doesn't it doesn't matter. But that that
89:17 should be nailed. Thank you. , my hydrocarbon gradient should extend from
89:28 little water contact. Start from the line here on the water contact and
89:35 up at some slope less than the gradient until you get the top after
89:42 top of crest to over here. the these these two elements. This
89:49 is fixed. This elevation is fixed the slope can be variable in between
89:56 . All right, okay. if I draw that slope so that
90:06 hit the fracture gradient from will the week off completely. No, they
90:14 . That's the dynamic equilibrium that I . That is more hydrocarbons come into
90:18 trap, an equal volume has to out the top but you still retain
90:24 oil column in there. So even you're at the fracture gradient, you
90:28 have a crucible retained oil column in . And he any comments or questions
90:40 this so far with, can you explain why the hydrocarbons won't leak off
90:48 ? Even the gradient that is the . Yeah, it becomes a
90:55 it becomes a dynamic equilibrium. So I um if I leak off hydrocarbons
91:03 , then that's going to move this to the left and now I have
91:09 space actually is going to move this down and I have more effective stress
91:14 to put more hydrocarbons in there. , so or alternatively a way to
91:23 of it as once you hydrofracking top influence, escape, you reduce this
91:29 point and the fractures seal up again so you you regain the retention
91:44 Okay, now this is um, emphasize this before that. These are
91:56 evidence of a of of a blonde . But when you have this
92:03 the seismic wipe out zones, disturbed , events and scarfs at the surface
92:09 tarts. Do they indicate the presence hydrocarbons in the underlying trap or
92:20 That it indicates that there's hydrocarbons or they're escaping? It doesn't really tell
92:30 whether you've got hydrocarbons or not If go back to um I guess
92:44 Go away. So in both of instances I'll have expulsion features like that
92:59 at the surface or in the overlying data. Thank you. But I'll
93:04 the same features whether I have um escaping or hydrocarbon escaping and I can
93:12 water escaping without any hydrocarbons. Let's I just I don't have a I
93:20 have a trap here. I could just hide her current. And so
93:26 the presence of those expulsion features. me I have this or I have
93:32 but it doesn't tell me which of two I have. So is that
93:47 that clear? Is everybody okay with ? No. The silk capacity of
94:01 has become an important topic with some the players in the gulf of Mexico
94:07 . And if we go over to mom, there's a lot of data
94:13 that shows that. Mhm. In section we have salt. The salt
94:20 you have the salts here sediments in . So it's very much like the
94:26 of Mexico many basins. And then the salt, we have these carbonate
94:32 that contains hydrocarbons. Um In the only limit on the retention in these
94:42 stringers is the seal capacity of the . And when we look at the
94:48 in those carbonate stringers, they're limited the frack, created the minimum horizontal
94:56 . And so the silk capacity of salt is the same as the fracture
95:02 or the minimum horizontal stress gradient. . And this is the this is
95:12 pressure data showing that. So here's our project leak off trend. I
95:18 leadoff trend and here are different hydrocarbon inclusions in the oil reservoirs, mm
95:29 . And they are all topped out this minimum leak off. Test grading
95:35 this minimum horizontal stress and so it the minimum minimum horizontal stress. That
95:43 the sealed capacity in these oil reservoirs the stringers encased in the salt.
96:03 . Um so that becomes important for sub salt play in the gulf of
96:14 now where we have these Reservoir beds up into three way closures against the
96:22 of the salt. Sure. And industry these are referred to as mega
96:28 , wow. Where these beds have pulled up by the salt extruding up
96:34 here and then out into a So the only limit on these traps
96:41 the seal capacity of the salt. it's the sealed capacity of the salt
96:50 is equal to the minimum horizontal stress . Yeah, there was a is
97:08 clear the the sealed capacity here? , limited by the salt and by
97:14 minimum horizontal stress. No, we also have top seal failure related to
97:32 . So here's a here's a cross from offshore Gambia, depart Gambia from
97:40 shown here in the in the tank , um and then a mix of
97:49 and shale shown here in the dark color. The reservoir objective is just
97:57 that, right in right in mm hmm. And in these
98:04 they are at there is stable pressure . They're stable Topsfield pressure today.
98:14 in the Miocene these channels, they the overlying sediment. So there's there's
98:22 floor, there's the base of one , there's the base of another
98:27 There's the basically the third channel, this channel ization, remove the overburden
98:35 these traps, reducing the vertical stress the mineral horizontal stress and causing the
98:42 too to feel. So this shows pressure depth data for that trap pressure
98:55 , depth here, all the leak test data here. Um rough fracture
99:01 here in the black dashed line. this is the this is the hydrocarbon
99:09 with the water gradient at present All right. When what happened with
99:15 examination is that we reduced the burial and in effect we moved this column
99:22 to here where it intersected the french gradient and in this case about half
99:28 the hydrocarbon column leapt off before it buried back down to here.
99:34 And so this is an example where get topsail failure due to exclamation,
99:40 the overburden, reducing the with a stress and the minimum horizontal stress do
99:48 have over the top of the Okay. Thoughts on mechanical failure,
100:01 of fault zones occurs under the same as top. Seo mechanical failure.
100:07 uh the idea that active, critically false leak is just, it's not
100:14 . And this is some become industry wisdom based on some papers by Mark
100:20 and his students out of stanford and just incorrect and it's incorrect because we
100:30 lots of examples of active faults that still retaining hydrocarbons and by active or
100:39 stress fault. We mean that the circle intersects the fracture gradient, causing
100:47 failure along the bounding faults, but that does not cause leakage. And
100:54 are two examples. This is from cusiana field in onshore Colombia. The
101:02 is down here where the gas cap an oil column here, it's sealed
101:07 this cusiana thrust here. And even this threat, this thrust is so
101:16 that the well wars only last about months before they're sheared off by the
101:21 faulting. Um, and, and We still retain a three billion barrels
101:30 amount of hydrocarbons in this field. this is an example of an active
101:35 fault and ceiling. This is an of an active normal fault. That
101:41 . This comes from the Eugene Island 30 field or posie fields in the
101:45 of Mexico. You see the fault , the reservoirs extending up to the
101:52 . So they're from trapped, trapped part by the fault, even though
101:57 faults are active. And so these faults Sealed pressures up to 300 C
102:05 these adjacent reservoirs. So even though active, they're sealing large pressures and
102:11 hydrocarbon columns. Now in the upper here is that the plot, that
102:20 the basis for this idea that critically false leak. And this is a
102:26 of odd plot. It's effective normal here versus shear stress here. So
102:32 similar to the more corn plot, hmm. And then these two bloodlines
102:41 the range of practical feel your These represent the range of possible more
102:48 envelopes around here With a mewling little interview legal .6. The different color
102:58 here represent different reservoirs where the dots open is where they're sealed and where
103:07 solid fills along here is where they're leaking and they're divided approximately by
103:16 Feel your envelope line. And so that sobek Adele concluded that the were
103:24 faults are critically stressed or where they critically stressed or active. They're
103:31 Whereas where they're not critically stressed where stress state doesn't intersect the failure
103:38 they're not leaking. Mhm. In for you, important point underlying this
103:46 that these these wells were drilled in rocks in basalt and granite. And
103:56 measure the fluid they had to leave gentle ease of World War open run
104:02 drill stem test for three months. these are leaking. But the rates
104:09 which they're leaking are incredibly small. effective permeability from those well tests Is
104:16 the order of 10 of the -3 10 to the -6 million dark
104:21 So there, yes, they're leaking the seal capacity is equivalent to a
104:29 or a shale topsail. So in in real life, we can have
104:36 active faults trapping large pressures and hydrocarbon . This is another example of an
104:47 ceiling fault. This is from but big board feels will be a psalm
104:51 in India. You see the naga coming up here and again. This
104:56 an active thrust today. And the are shown here in the white pattern
105:03 oil water contact extending several 100 m here, but deeper than the thrust
105:11 off here, showing that we've got ceiling, the ceiling thrust fault trapping
105:18 oil columns in the hanging wall So even though it's active, it
105:22 to seal all right. And so is this is a paper that I
105:32 some others published on C. 2 Traps. And what causes the
105:38 along the fault zones in the And those traps come from southern Utah
105:47 the Paradox basin here, um in in this part of the paradox
105:54 there are hydrocarbon accumulations and there are ceo to accumulations of all these
106:00 Well let's just show up active oil gas fields. And in the middle
106:06 the basin here We have these hydrocarbon . 0. 2. So you're
106:12 trapped accumulations. This is this is example of one of them. This
106:18 originally drilled as an oil trap and to contain C. 02. This
106:23 the wellbore from that original World Alright, so this is a three
106:35 . View of the CO two This is a structured contour map on
106:40 horizon. We have an antique line off to the northwest here With Co
106:47 accumulations here. On the upside of CO. Two water contact in here
106:57 the up thrown side of this co water contact and all along these
107:04 we get C. 02 geysers seeps springs along the surface traces of the
107:10 . This is this is an example one of the geysers that occurs along
107:15 fault. This is an example I where this fault goes under the green
107:21 And you get the co. two in the water where the fault is
107:25 CO two to the surface and these are completely inactive. They're completely
107:36 Right. But what's causing the leakage the high fluid pressure. So here
107:42 have pressure depth grass for 5. of the linkage sites in one of
107:49 non making sites. So here's my static gradient. There's my my fracture
107:58 , there's my water gradient, My . Two water contact and the
108:04 02 pressure line extending up to where hits the freshman radio and causes
108:12 Similarly, if this accumulation got the godin gradient fracture gradient, the water
108:20 , the CO two gradient growing up the CO. Two contact here,
108:24 the fracture gradient and causing leakage at point. This other woodside geysers.
108:32 story with the star ingredient fracture Water gradient. Co two gradient extending
108:39 . Getting a fracture gradient causing leakage the fault zone up to the top
108:45 . Yeah, same thing for these other accumulations bubbling spring and 10 mile
108:53 , wherever the leakage occurs, wherever CO two gradients hit the fresh ingredient
108:58 in here. Now we also have in Fernando the pressure depth grab from
109:06 non leaking C. 02 accumulation. , there's my fracture experience. There's
109:12 fraction with a static radiant and black radiant in red Water gradient in blue
109:18 then the co two gradient. We here in green. So here is
109:23 the weekend. I have a very effective stress retained between This year two
109:30 the minimum horizontal stress fracture gradient. . Very different than all these other
109:37 where the effect of stress is zero the crest of all these traps.
109:42 . And so there. The conditions week. Ege of the fault
109:48 Is the same. Is it the for false songs as for top seal
109:54 . And the leakage conditions for 2 traps is the same as for
109:58 and gas traps. Alright, here's some other examples of leakage occurring
110:09 the fault zones where it occurred by injection, raising the reservoir pressure.
110:19 is from an example of northwest The platforms here and here we're injecting
110:28 into the reservoir. And after several of injection they started bubbling hydrocarbons out
110:38 of the reservoir at this point. that occurred because again they increase with
110:45 injection they increased that fluid pressure to the fracture gradient. This is an
110:52 from deepwater offshore brazil where we have fault extending to the sea floor and
111:00 this case oil oil emanating up from from that fall from the sea floor
111:08 again in this case the there was water injection occurring that raise the risk
111:15 pressure to intersect the fracture gradient and the hydrocarbons to be expelled along at
111:24 . Okay. All right. I gave you these conversion factors in
111:34 . They're important for being able to mud weighs and confront those mud ways
111:40 pressures. All right. But so gave you I think I included this
111:47 an exercise. Yes or no? . Okay. Mhm. So take
111:57 few minutes and and and go through . Take this information. The kelly
112:04 the water depth leak off. Test information integrity test data both in pounds
112:11 gallon. And what I want you do is convert those pounds per gallon
112:18 to P. S. I. the formulas to do that are given
112:27 in here. So go ahead let's why don't we take 2020 minutes take
112:39 time to to do these calculations and take a break And we'll come back
112:46 20 minutes and talk about the Okay let's go ahead and talk through
113:14 exercise aren't. This is important because shown here is a daily drilling report
113:20 typically how all the information is reported we then use in these pressure depth
113:25 to calculate um you know week off and gradients and all that good stuff
113:31 we've just been doing. Okay So to get the depth and people and
113:48 line for the L. A. . And the F. Eight
113:52 I. T. You want to the total depth subtract the water depth
113:59 the kelly pushing. So for the . O. T. It's 6
114:04 : 2 -1054 -35. For the the information integrity test it's the total
114:15 KB 10 406 minus the water depth the kelly pushing again. So it
114:22 out to 1046 -1054 miles 35 And that that often trips people
114:32 Is that clear to everybody? Yes . I have a question sir.
114:39 . So my question is on the total debt. Yes the deaths in
114:45 P. S. A. So do we have to add the
114:49 from the calibration to that? Oh . So um yeah from for both
114:58 these of the end for the No for the yeah both both of
115:06 are depth from the kelly bushing. so after the calibration the debt.
115:12 . Yeah thank you. So you the depth below the mud line for
115:15 of these. You need to subtract of these numbers. Okay. Okay
115:23 then for the and then for the um You convert the mud wage 13.1
115:34 13.2 To see using this conversion factor .052. And then you multiply that
115:46 the times the depth and subtract the of the water column. And for
115:56 of these that's The .443 months Times . The water density times the water
116:05 gives you the weight of the water . And by subtracting that way to
116:09 water column you get the you get pressure relative to a depth of one
116:16 . So you subtracted the weight of water column from those two pressures.
116:28 . Yeah for the M. T. It's a little different because
116:33 have to you have to pressure measurements but your depths our feet some speak
116:41 to correct these defeat Balon bloodline. of track just the 1054. So
116:48 the depth feeds up c minus just water depth. And then to get
116:57 these pressures to pressure below the mud . You take the pressures and subtract
117:03 weight of the water comb .443 times to get these these numbers.
117:16 Okay comments or questions on that. . All right we'll go ahead.
117:34 okay and in what we do it's to convert all those data to depth
117:44 for um to to compare steps from to compare data from fields with different
117:55 . Mhm. And for to assess connectivity. You need to calculate everything
118:02 to a subsea data. To calculate men we need to look at a
118:10 of black and white line data. depending on what we're doing we may
118:14 to use a subsidy data or a one month line data. Okay and
118:24 and the reason for that is that leak off pressure increases from the sea
118:31 . Whereas the poor fluid pressure increases sea level. So when we want
118:35 look at the fracture data we need normalize the leak off pressures to mud
118:43 both the depths and the pressures. evaluate fluid pressure. We need to
118:51 at everything relative to sea level and we need to make sure that we
118:59 both depth and the pressures. We the same data. So for like
119:08 for these two fields, if we at everything in a subsea view data
119:15 the reservoir pressures line up with the off test data fall into different
119:25 I'm so for reservoir connectivity we need use the sub c reference for ah
119:37 minimum horizontal stress and overburden calculations. need to use the death blow mud
119:44 reference. So depth below the mud for the X. Axis, Impressionable
119:48 one line for the Y. When we do that, all these
119:53 off points will line up into one that enables us to calculate the minimum
119:59 effective stress. Sure. And when looking at depth below my line of
120:09 below my line we have to make we use the corresponding step below them
120:15 or pressure below online data. But and this must be people on one
120:20 . Both this and this must be obscene. Okay, so to summarize
120:34 pressure data section to calculate pressure for weight data, the height of the
120:40 column should be used. Um And applies to leak off pressure data reported
120:45 mud weight like we just saw in scout ticket gradients are going to vary
120:51 on the reference level. So the will vary depending on whether you use
120:56 subsidy or a mud line data model columns of a constant gradient will have
121:05 sub secret agents at different depths to connectivity between wells data should be plotted
121:12 depths of C to assess vertical, stress and leak off pressure or minimum
121:19 stress in different wells. It should plotted in depth below the mud line
121:23 preferable or mud line and never don't confuse the mud line and the subsea
121:31 diatoms. So the summary for this , mechanical seal capacity is expressed as
121:42 hydrocarbon column height, a truck and before the top seal hydraulically fields or
121:49 by financial hydro fracturing traps. The failure due to hydrocarbons can still retain
122:00 . We looked at those examples where were at failure, but they still
122:04 thousands of feet of hydrocarbons protected traps those traps that are hydraulically connected to
122:10 weak point such that the pressure is and modulated and the aquifer pressure will
122:17 exceed the local topsoil capacity, critically faults concealed, so even though faults
122:24 be active today, they can still large pressures and column heights, leakage
122:31 thoughts occurs where the total food pressure the fracture gradient. It doesn't occur
122:36 the faults are active. It does where the total fluid pressure equals a
122:41 gradient, just like tom seal failure this is true for both hydrocarbons and
122:50 and that mechanical seal capacity is important traps that are, it's shallow depth
122:55 bloodlines. So there's not much overburden hard over pressured settings where the aquifer
123:02 pressure is getting close to the fracture , its subregional structural height so that
123:09 apex is that I showed you earlier a trend of full separated by
123:17 And they're important for a fluid expulsion . Like a seismic wipeouts is observed
123:22 the seismic data on the sea floor the surface and these expulsions owns or
123:28 see those whether you have hydrocarbons or . So you get the same expulsion
123:37 , whether it's due to overpressure dwyer due to overpressure hydro currents.
123:47 All right. So that's that's what want to stop for today.
123:53 We're early again. We went through much faster than I expected. We'll
123:58 again next friday, Same place. the same zoom link that we used
124:03 friday and we'll talk about riffs and growth falls and do a review of
124:11 for the midterm. And then up saturday we'll start with the midterm first
124:18 in the morning and then going to about false fields and salt tectonics and
124:23 to talk about full thrust belts, you have a question I'm regarding the
124:31 . Are we going to have a guide like we do for the final
124:37 . Um Well, yeah, just . Just before the exam will have
124:44 review presentation and that will be that be your study guide. The the
124:51 tests will come pretty much directly from midterm review slides. Is that gonna
124:58 posted on blackboard? The review was on blackboard. Yes I didn't see
125:06 midterm review one. The final review on there. Okay I'll check to
125:11 sure the midterm review is on there well. Um When you go to
125:16 you'll see. I've also made a with references that have all the basic
125:20 for these things that we've talked about you want to by the way your
125:28 what will be the format for the ? Will we have to print anything
125:32 or we can do it on the ? You can do it on the
125:37 . I will send it to you a as a power point file that
125:41 can then write in type and draw that at the at the end of
125:50 be um it'll be about two hours I'll have you sent to send it
125:54 to me at the end of that hours. Okay Thank you. You're
126:05 . Any other comments or questions I for you all. What what do
126:11 think about this? Mix of exercises lecture? I really like them.
126:19 helps to understand the material and give a chance to kind of check our
126:28 . Okay good. In my experience works well when we've done face to
126:33 but I wasn't sure how it would in these virtual sessions. So thanks
126:38 that feedback. Alright, well, the rest of your weekend. You're
126:47 early. It's like a snow enjoy the rest of the weekend and
126:51 see you next week. It will I'll be virtual again using the same
126:55 that we used this weekend. Thank you. Bye
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