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GEOL6350-Advanced Structural Geology - Day2 AM 02-19-2022
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00:00 started I moved. So this this we're going to talk about geo mechanics
00:12 fractures. Okay, that's better. , so we're going to talk about
00:34 three geo mechanics and fractures. And we'll take a lunch break. And
00:38 in the afternoon we'll talk about top failure. And we'll use the things
00:42 we learn in this section about Hugh to understand how Topsfield failure occurs when
00:48 occurs. What are the conditions for journalism? So, here's an outline
00:56 what we'll cover this morning. We'll about fractured definitions of what are called
01:02 1, 2 and three fractures and what are called joints And Beef,
01:09 are both Mode one. These are fractures. We'll spend most of time
01:13 about insurance and then we'll talk about geometric characteristics, a budding relationships and
01:21 that tells us about timing and como that we observe on the joints that
01:28 us about the joint formation. And we'll talk about mechanicals photography, and
01:34 layering affects the different joint sets that get. And then we'll talk about
01:41 parallel fractures, what are also called and these. To understand these,
01:47 have to understand the effect of fluid on the mechanics. So, to
01:52 that, we'll talk about more calm stress orientations, the role of fluid
01:58 in the implications for fracture orientations. then we'll talk about time of formation
02:06 joints and beef. And the last we talked about hydro fractures or induced
02:13 . They follow all the same all same rules or characteristics as Alright,
02:20 natural fractures. And then lastly, talk about the impact of natural fractures
02:25 well performance and unconventional. Okay, this now shows the different types of
02:34 . These are Mode one which are opening fractures. So all the all
02:40 displacement occurs perpendicular to the fractures to fracture surface. In Mode two sliding
02:48 shear fractures, there's sheer occurs along um parallel to the fracture surface,
02:57 to the long dimension of the In Mod three fractures tearing their shear
03:05 . The displacement occurs again parallel to fracture surface, but parallel to the
03:11 dimension of fracture surface. So, are Mode one fracture or what we're
03:20 to talk about today. These are joints and what are called beef bedding
03:25 fractures. Their joints when they form high angles to the bedding, typically
03:31 90° when their bed parallel, they're beef or bed colonel fractures. And
03:39 are distinguished by the lack of shear are both Pure Mode one Pure opening
03:43 tensile fractures. Right? And these are some examples from the marcellus
03:54 You see these everywhere. These are most common geologic features. You see
03:59 the surface here, you see all vertical fractures. And these are these
04:05 joints There are two sets here, on this plane, in one on
04:10 plane. Here's another set also from marcellus shale C1 joint surface there Wanted
04:20 to adhere and in the pavement surface , you can see them again.
04:25 set here in another set going through . Really? Alright, so these
04:37 all more examples from the Marcellus shale in the pavement. You see one
04:43 going here in another set going roughly to that. Here's what they look
04:51 in a cliff face. The main here and the secondary set roughly represented
04:58 , not very well represented in this here in a close up of the
05:04 . You see the main set going here and then you see secondary sets
05:11 here and here, also going through through the bedding. Okay, right
05:23 we um We turn these on J and J two depending on their timing
05:32 the J ones are the are the that are first to form J 2's
05:37 be the second form. If we additional sets, there would be J3
05:41 J4. So the subscript tells you set is the first to form and
05:48 can tell which is the first informed the a budding relationships. You see
05:53 are through going and the J two's against the J ones, fractures,
06:01 propagate against an open across an open . So the the successive ones terminate
06:10 the proceeding ones and that gives us sequence of generation. So the through
06:16 ones through going once here with someone the secondary set here that terminates against
06:23 would be ours. There we Okay along the joint services themselves.
06:39 get these features which are called palamos GMOs because they look like they look
06:44 a feather. Here's one example, another example here. You can see
06:52 sort of radiating strong coming out this , what are called hackles and then
07:01 termination services here that represent the different termination surfaces of the joint as it
07:15 . This is a block diagram showing the joints form in relation to those
07:21 features. Wow, we'll have a point here at the origin that represents
07:28 initial flaw where the joints initiate. then these surfaces that form the luminous
07:36 represents excessive propagation of the of the , mm hmm. And then these
07:47 see these arrests were called arrest lines represent different stages in the joint formation
07:56 the joints are or Parallel to signal in the in the open, Perpendicular
08:05 Sigma three. So that's our maximum stress and our minimum compressive stress.
08:12 the joints themselves will be in the one sigma two plane. So here's
08:24 example from the marcellus. I see large joint here, you see these
08:32 promos features emanating from the center of joint behind the geologist here, brunch
08:39 the joint propagated out in this And then these arrows along the twist
08:51 indicate the joint of the direction of propagation. So it starts as a
08:56 back here and then grows basically regularly an ellipse shape out in this direction
09:03 out in this direction and out in direction. Yeah. So here are
09:13 examples of mod one fractures in core are just open fracture harding's are essentially
09:24 , with no mineral crystallization here, have a fresher with some cement in
09:37 . And then the cement is important it shows that these things formed at
09:42 depths within the crust. Here's another of vertical fracture in this orientation,
09:50 lined with cement in this case. these are all vertical fractures. These
09:58 betting parallel fractures, expansion fractures or . From there parallels betting. And
10:05 usually filled with calcite, sometimes with or gypsum typically calcite. Um And
10:14 , let's talk about in a minute these require high fluid pressure, commonly
10:20 with hydrocarbon generation, require that high pressure to get this this sub horizontal
10:30 and with that high fluid pressure comes sanitation. Here's an example of joints
10:40 the Woodford shale and in this case the joints are filled with vitamin indicating
10:46 these joints these joints formed essentially during generation. Here's another example of multiple
11:01 sets And here you can see that most continuous one is this, this
11:10 three, all the others terminate against . So we have the J1 set
11:18 through here. J two terminating against J 1's going through here, there's
11:25 example And then this through set J terminating against the J 2s. So
11:34 can use those a budding relationships to us the time of the relative timing
11:40 different choices. Near some spectacular examples joints from arches, National Park.
11:53 joints in arches or what or what read to the authorities forming in
12:00 Things like delicate arch. You can the joints that's kind of curvilinear through
12:05 . So they're not they're not perfectly on a kilometer scale. And here
12:11 see a different view received one set through here. Those would be the
12:18 ones. And then you see the set terminating against the J ones.
12:23 would be the J two. Um then An artist here, you have
12:27 these two sets, the J one J two. Okay, here's an
12:38 from the eagle ford shale in south . See all the joints going in
12:43 direction And again, you see two , the main set going in this
12:49 and then a secondary set. The two is terminating against the J.
12:52 here in giving you this step like to the crop pavement. Okay,
13:06 this is another shot of the Eagle . We have the two joint
13:10 Mhm Chain one and Jay to the one being that through going set J
13:17 terminating against it. And in this we see another feature, we see
13:24 more ductile layer here that the joints against. And this this highlights what
13:32 call mechanicals photography where we have joint one set of bedding, mm
13:38 No choice in another set. And adjacent to that are below that we
13:43 a different set, different set of . one and J. two that
13:49 propagate through this mechanical boundary layer. so this this layering sets up what
13:58 call mechanical strategic graffiti where we have jointed set and on jointed and then
14:05 abetting the different joint of set below . Okay, this is another
14:16 This is from the bristol bristol Bay . I talked about where you see
14:22 highly jointed layers here, some not jointed layers here with some a few
14:30 going joints and then non jointed layer and another jointed layer here.
14:37 this would be another example of mechanical graffiti where each one of these different
14:42 represents a different on a different set joints or fractures. Mhm. And
14:52 an example of mechanical security from the shale. Um Here's a good out
14:59 view where you can see um The going this direction, one set of
15:06 going in this direction and most of joints terminating against the shapley layers,
15:13 more ductile layers than the Monterey. each one of these layers represents a
15:19 layer of mechanical Stratan graffiti And here the right is a close up of
15:25 here, you see two joint one here and one here to joint
15:31 , neither of which propagates through this ductile layer, sending up a mechanical
15:36 afi within each of these different Right, okay. And here's the
15:47 we use to describe these different joint . So, here's a block diagram
15:53 vertical faces, pavement here. Um we get these through going joints or
16:01 zones typically associated with faults. We through all the different layers and then
16:10 we have confined joints within each of layers that terminate against more ductile
16:16 That would be one confined joint That would be a second confined joint
16:21 . The third set. And in 4th and in between, we get
16:28 unknown fractured units viewed in pavement. see the different joint sets, The
16:36 joint set, the J one being most through going. And then J
16:40 RJ's three is terminating against that through joint set. And these are both
16:46 these would be what we call systematic where there's a consistent orientation to all
16:52 joints when viewed when viewed in When you found the ground surface
17:01 Right now, the joint spacing is proportional to the mechanical layer of
17:13 And what's shown here is cross part joint spacing versus mechanical layer thickness.
17:23 , we're plotting this spacing versus this . And you see in this cartoon
17:30 the joint spacing is proportional to the . The thickest layer has the widest
17:36 . Intermediate later has an intermediate spacing layers have the closest spacing. And
17:44 we typically see that an outcrop but not a very it's not very mathematically
17:52 relationship. So on this cross each one of these points represents a
17:58 set of joints with a different mechanical thickness. And if you try and
18:03 correlation through that, you see the coefficient is pretty poor. So there's
18:10 really a linear relationship. There's a proportionality but it's not a rigorous linear
18:22 . Okay, so that was all joints or vertical fractures. Now we're
18:26 to talk about bed parallel of horizontal mode one tensile fractures or what
18:33 also called beef. And this is cartoon looking looking at a cross
18:41 The short lines represent bedding planes and this lip soy in the middle represents
18:49 betting parallel fracture or a beef And these are typically calcite film.
18:57 see the most commonly inorganic cal Correa's . We think they originate from the
19:03 of the organic material in these shales they open more or less vertically so
19:10 crystal fibers within them are straight in . Their occurrence or intensity correlates
19:19 But the organic richness, the thermal , the over pressures and a mechanical
19:26 . So the more intense the anisotropy the layering of the more common these
19:39 So here's some examples of beef from . This is from Haynesville shale and
19:45 texas Louisiana. See betting services and the shale here um on a compacted
19:54 here, a good bedding surface here then this bed parallel fracture calcite filled
20:01 in the middle. This is another the Permian basin, Wolf camp
20:06 You see the betting is well defined this one with any calcite film bedding
20:13 fracture here in the in the And these are these are other examples
20:22 the of the cement that fills in fractions. And you see you get
20:27 nice vertical crystal fibers growing perpendicular to to the to the bed and caribbean
20:36 to the edges of the fracture is that the vertical nature of the factors
20:42 that these open just vertically without any of sheer on them. Mhm.
20:53 So here's here's another example, this from the vodka muerta shale in
20:58 See the bedding surfaces here really, ball to find betting. And then
21:05 getting parallel fractures or beef surfaces And this is another example from art
21:20 Argentina. And this is a this a nice example because it shows how
21:25 some of these things can be. a single, a single betting parallel
21:30 fractured, extending along all this way outcrop. Okay, here's a close
21:37 of it, you can see it's filled with calcite quite thick in this
21:45 and here's another example from marcellus you can see the bedding roughly there
21:52 there And then these bedding parallel fractures beef here here, here and here
22:00 then some other fractures here that are or less betting peril that kind of
22:05 situated cut across betting as well. , so in in general these things
22:18 when you have um hi horizontal stress a minimum the vertical stress. And
22:28 allows these things to basically pop open to betting. You can also get
22:40 spending parallel fractures just from sunroof from removing the overburden. And that's
22:46 here with these cartoons where in depth rock is subjected to hi confining stress
22:56 you do. You unearth that as raise this to the surface, the
23:02 stress is reduced and the horizontal stress the same. And so as these
23:08 approach the surface, you get bedding fractures without cement in this case.
23:13 these are what are called sheet You see these most commonly in in
23:22 and intrusive bodies. Is there under ? The vertical stress has released the
23:28 stress remains the same and that gives to the sheeting fractures that are parallel
23:33 the parallel to the landscape. Carrollton surface, and the difference between these
23:43 the previous ones is these form close the surface, so they don't have
23:47 cement as the cement in these indicates they formed at a much greater
23:59 And we can we often look at fluid inclusions in the cement to identify
24:05 timing, the relative timing pressure and that these things format. Okay,
24:19 , let's let's take take a quick here, give you a few minutes
24:24 get up stretch, get a cup coffee, whatever, and we'll come
24:28 in in five minutes. We'll come in five past. Don't.
24:35 Talk about the mechanics of fracture mechanics the relationship of the fractures to the
24:41 and the strains. So we talked stresses and strains yesterday with the different
25:04 of fractures. And now we're going talk about that in a little more
25:07 . So we've got a block diagram with Or signal one. The maximum
25:12 stress, Sigma, three, the compressive stress, and then two faults
25:19 fractures forming At roughly 30° to the compressive stress. And then the stresses
25:28 on those sheer plans are the sigma the normal stress acting on that fracture
25:36 , and cow, the shear stress on that normal plain. So the
25:41 stress and shear stress, Addressed the of signal one and signal three,
25:47 on that shear plane. Now, we measure the fracture strength of
26:01 what we do is put it in what's called a tri axial, we
26:06 a piece of core and attracts your device and basically push it stress it
26:13 to the length of the core until fractures. And then at that point
26:18 record the stresses imposed on the on vertical and horizontal dimensions. So this
26:27 be our sigma one sigma three and we plot them on this type of
26:34 is called a more cool diagram Where signal one represents the greatest stress imposed
26:44 three is the minimum stress. And construct this circle based on the diameter
26:50 71 and 73. And when we that for successful successive experiments with different
26:58 , different signal ones and different signal , we get these different stress
27:03 the black one, the red The Blue one here and they are
27:09 tangent to align shown here in that tangent is called the more coon failure
27:19 . And that's the line tangent to success of stress circles. And that
27:25 gives us the normal stress and the stress acting on the plane on the
27:32 failure plane for any combination of normal Well for any commendation of signal one
27:39 signal three. Now this more column line gives us the failure criterion for
27:54 fed shear failure. So that's that's guys. If we extend that into
28:01 tensile round here it becomes a lip , the normal stress becomes negative and
28:09 are the conditions under which we get fractures joints or or beef. So
28:16 kinds of joints that we see form we have although small, small diameter
28:27 the stress circle and a negative value at least one of the principal
28:33 Those are the conditions that give us tensile failure and joints and you can
28:45 it too. To get into that of the failure envelope, we have
28:51 have a very small a small diameter and we have to have something that
28:59 move that stress circle into the into negative realm here on the normal stress
29:06 . And what does that is the fluid pressure. So the requirements for
29:15 failure in terms of stresses are low stress, A negative signal three in
29:22 low differential stress of small diameter to stress circle. and when the resulting
29:29 one fractures are um vertical, we a vertical signal one and we get
29:35 when they're horizontal, we have a signal wanting to be for the betting
29:40 fractures right now. Um But what plotting on that more cooling diagram or
29:57 a wrong this access is really the of stress. It's the total stress
30:04 the fluid pressure. And that's and shown here where schematic more column
30:17 the effective normal stress along this shear stress along the saxes the failure
30:24 here where we get the shear fractures then there's tensile realm here where we
30:29 the tensile fractures and effective stress is total stress minus the fluid pressure.
30:39 so what that food pressure does is these stress circles progressively to the left
30:47 they hit the, until they hit fracture on floats. If I have
30:52 large scale or circle the large differential , I moved that circle to the
30:57 and I hit the fraction envelope and get shear fractures when I have a
31:02 circle and I moved that circle to left with increasing fluid pressure. I
31:08 it in the tensile realm here and the tensile fractures the joints or the
31:14 the beef. So these these tensile require of high fluid pressure.
31:29 and here's here's how that this is cartoon of how that works. Um
31:37 start with high vertical stress out here I increase the fluid pressure. I
31:43 this point to the left to get vertical effective stress. If I increase
31:51 fluid pressure even further, I continued with his point further to the left
31:56 I get this vertical effective stress with high fluid overpressure. When I move
32:06 circle to the left, with a overpressure and I get this vertical effective
32:12 with a low overpressure, the stress that generates failure conditions, it is
32:19 fairly large diameter circle. Now with high fluid pressure continue to move this
32:33 to the left. Somewhere over here I got this vertical effective stress with
32:38 high overpressure and now the circle the results and failure is much
32:47 Then with this less fluid pressure if I progress that even further,
32:57 can move those that stress circle all way into the tensile realm here where
33:02 stress circle intersects the failure envelope. this tensile region and generates the mod
33:09 joints or or Betty grable joints. grable fractures. You have a
33:17 Apart from sigma one sigma three will the diameter of the circle. That's
33:26 that's all the control. Well, one sigma three and the fluid
33:31 Okay, okay, I know this pressure moves it along the the normal
33:37 in the fair envelope. I'm just to understand. Okay, so sigma
33:43 sigma tree, they both control the of the circle. Thank you,
33:49 . And as the as you increase fluid pressure, um you can only
33:54 a smaller stress circle before you hit failure envelope. So the the fluid
33:59 is a secondary effect on that on diameter of that circle. And
34:08 talking specifically here about the circles that in failure. Okay. All
34:21 alright, so now we're gonna talk the stress orientations based on these two
34:26 principles. The stress orientations with respect the joints of the beef.
34:37 So, for for both joints and , we have these mode one fractures
34:43 the opening is perpendicular to the plane the fractures and ς. one is parallel
34:54 the plane of the fractures in Sigma is perpendicular to the plane of the
35:01 . When Sigma three is horizontal, get the vertical joints. When Sigma
35:07 is vertical, then we get the for the bedding parallel fractures?
35:14 In the The strike of the joints of the joints where we have the
35:20 fractures. The vertical mode one the of those is parallel to the signal
35:26 that's imposed on fractures so we can that strike of the joints to tell
35:33 the signal wanted. A signatory were the time of joint formation.
35:46 so here's a there's sort of a point or a quiz. Well we've
35:52 I showed this before. We've got J. one and J. two
35:56 J one is attending in this direction is Northeast. J. two is
36:01 to that, so experience west. what were the orientations of sigma one
36:07 three during the formation of each of joints starts if I come back to
36:41 schematic, we're looking at joints like with the vertical joint or fracture here
36:51 signal one is parallel to the strike that joint. So if I come
36:58 to this, If my J one northeast what's the orientation of my signal
37:04 at the time of joint formation? , yeah, northeast it's parallel to
37:12 joint set, So Sigma one is to be disorientation. What Will Sigma
37:17 ? B. Northwest, northwest perpendicular that. Now, if we go
37:29 J2, we've got a northwest striking . What does that tell us about
37:36 ? The maximum stress. I think one is not peace. What kind
37:53 things? No. For for these two, sigma one is going to
37:58 northwest, It's going to be parallel the strike Of the J two
38:04 So for J two Sigma 1 will northeast. Signal three will be
38:10 And so the stress orientations Flipped 90° the two times the times of these
38:17 different joint cells. And that's that's possible because the values of sigma
38:31 sigma three are so close, mm . Because to get these tensile
38:36 we have to have a small diameter . The values of sigma one and
38:41 three have to be pretty close to other. So it doesn't take much
38:45 a perturbation To swap the orientations of 90°? Mm hmm. And that's that's
38:52 we get these um orthogonal joint sets we still frequently see but in
39:03 Okay. Any questions on that. , I'm gonna go ahead. So
39:24 do the same mental exercise with the . three joint sets here. J
39:30 , J 2 and J three. one strikes northeast two strikes north.
39:38 three Strikes East West. What were orientations of signal one and signal three
39:45 the formation of each one of these ? Starting with J one. What
39:51 the orientation of sigma? One sigma for J one sigma one is not
40:00 . Why sigma tree is not Perfect. How about J.
40:08 Sigma one will be not in the . Doing this just Yeah,
40:15 Good. How about the last J. three, J three,
40:29 1 is East West and Sigma three not to salt, yep.
40:35 Good. Mhm. So here we've three joint sets with different orientations.
40:44 and that implies that the stress orientations three times during the formation of these
40:52 and because of the a small diameter that stress circle, it doesn't take
40:58 for the orientation of the stresses to during these joint formations term.
41:10 now, one of the things we've recently is that the joints we see
41:19 outcrop at the surface are not necessarily same as what we see in the
41:29 in this, we learned this from marcellus shale and this is on mm
41:37 , pavement in the marcellus shale, pennsylvania. You see the different joint
41:43 , anyone going through in this there's another one and then jay to
41:49 budding against that and there you can the budding relationship really clearly. And
41:58 expected all these joint sets to be in the subsurface and we found that
42:03 was not in fact the case. this is a map of joint certs
42:14 the marcellus play here in new york you see there are two very systematic
42:20 to the joint sets of surface of the dominant set trending northwest southeast and
42:27 a secondary set roughly perpendicular to that northeast or east northeast rotating slightly through
42:37 in these, these would be the winds the northeast set. And these
42:41 be the J. Tunes the northwest . And what's interesting is that these
42:47 J. Ones our east northeast trending to the present day Signal one Signal
42:55 . Max. If we go south pennsylvania, we see similar observations jane
43:07 trending roughly northeast & J. two trending northwest southeast and again parallel to
43:17 present day maximum horizontal stress in the orientation. All right. But when
43:28 look at, we look at horizontal and more orange logs trending in this
43:38 orientation. We see that that J that is not present. It's absent
43:44 the subsurface. When we look at horrible image logs and horizontal core,
43:51 only see the northwest trending joint So in in out drop where we
44:02 these two sets, the J. In the J. 2's in the
44:07 . We only see the tunes. these um so that the J.
44:19 are just not present in the in subsurface in there. They're an artifact
44:27 present day horizontal maximum stress. And so here I've got a couple
44:37 slides to talk about the history, burial history of the time and joint
44:43 . Mhm. So here on the , I have a burial history diagram
44:49 the marcellus trending through here and the colors represent the different um different organic
44:59 . So here we are in the window. And if we look at
45:08 inclusions from the, from the we see they contain both oil and
45:15 . So they formed either oh they basically at the same time as later
45:23 maturation. And we see a low population here representing formation during burial and
45:33 high temperature populations here with hydrocarbon inclusions formation pretty much at maximum burial or
45:43 during helpless. And so this is us that these fractures these joints formed
45:51 the maximum burial and during early Similarly, if we look at veins
46:06 the Eagle for joints we have both parallel and perpendicular veins, joints,
46:13 of which they contain hydrocarbon inclusions indicating the fractures post dated hydrocarbon generation.
46:23 this is a burial history for the for looking at a temperature vs.
46:31 time going from pretty vicious to present . And it shows that the um
46:44 ford went through maximum burial at this in the in the oil window.
46:50 so the joints must have formed here the maximum burial or shortly after during
46:57 early stages of uplift. Okay, we can use these observations to make
47:09 of the fluid pressure. Uh So in this, in these examples
47:16 been talking about in the marcellus, joints we know from the Fluid inclusions
47:23 about 25,000 ft. And we can some of these relationships to calculate what
47:30 overpressure is That's required to form those at 25,000 ft we know that sigma
47:40 . Is our signal one And that with that at a rate of about
47:45 cm per foot. Sigma three is H Men. And that typically is
47:51 70% of signal v. And then water pressure increases with depth at Rate
48:01 0.455 p. s. sacrifice. we can use these things to calculate
48:07 fluid pressure is required to get those joints in the marcellus. Thank
48:18 So the key thing here is that joints require fluid pressure Equal to about
48:23 three. So, to get σ We can calculate signal 1-25,000 ft.
48:32 about 25,000 ft of depth times one foot. It gives me 25,000
48:40 Sigma three In 25,000 ft is about of signal lines. So it's about
48:48 Of this 25,000 Which works out to a 17,500 cc. So that's my
48:55 three. That's a total fluid pressure for joints. Hydrostatic pressure at 25,000
49:05 . Just the weight of the water alone Is 25,000 ft, times that
49:13 And that gives me a hydrostatic water of 11,375. So that's not sufficient
49:22 generate these joints. I need additional and the magnitude of that overpressure is
49:30 difference between these two. So it's 17,500 -11375 shown here. So we
49:41 6125 pounds of overpressure to generate the that we see in the marcellus shale
49:51 ft. So when we when we at these joints, we can use
49:59 relationships to calculate what the approximate food is then, or what the food
50:07 was that generated those joint sets. , and correct hydraulic fracturing or hydro
50:22 , just form under all the same as natural fractures. We need the
50:29 fluid pressure to reduce the effective I don't need the high fluid pressure
50:36 get that effective stress into the tensile . And this is you know when
50:43 when you do a frack job, is why you see all those tank
50:47 and pump trucks out there to pump fluid down to generate the high fluid
50:53 . And like in the case of marcellus, when you hydro fracture
51:01 you need to generate a fluid All right, Equal to the 17,500
51:09 . So it requires a lot of and a lot of pumping to get
51:12 high fluid pressure and just like a fracture is what that does natural
51:20 What that high food pressure does has the stress circle to the left until
51:26 intersects the failure envelope and intentional region And just like natural fractures. The
51:39 fractures propagate parallel to Sigma one. , when these fractures form whether their
51:46 or hydraulic fractures, The strike of joints is always parallel to signal one
51:51 Perpendicular to Signal three. And that's this cartoon of a horizontal well
52:03 With fractures stimulated by hydraulic fracturing. these fractures propagate parallel to sigma
52:13 In this case same h max hydraulic follow all the same relationship as natural
52:28 and here's here's an example from the shale up in Dakota, mm
52:35 You see these black lines of structured indicating just the bowl shape to the
52:41 basin here with the with the bargain . The present day maximum horizontal stress
52:51 northwest southeast here, and when we at the well boards, all the
52:57 fractures and the hydraulic fractures follow the trend northwest, southeast parallel to the
53:04 present day horizontal stress. See that here, we don't see that.
53:11 some reason, I don't understand. is maybe on the nests and an
53:15 , and that's divert the fractures. elsewhere in the basin, we see
53:20 northeast southwest orientation to the fractures parallel the maximum compressive stress. Thanks that
53:36 . So here's an example from from the the Guilford, in what
53:43 looking at here are micro seismic events that formed during hydraulic fracturing. These
53:52 the well boards here here, in different colored clouds represent different different stages
54:02 the hydraulic fractures? And you see overall the east trend northeast southwest parallel
54:09 the present day maximum compressions trust parallel the S. H. Max.
54:16 and that's independent of the wellbore Here, you see a world war
54:21 perpendicular to that S. H. in the hydraulic fractures extend northeast
54:30 Here's another well war with north south and the fracture. The hydraulic fractures
54:37 follow the same northeast southwest trend parallel the S. H. Max.
54:43 these hydraulic fractures extend parallel to the . H. Max, just like
54:49 fractures due here's another example from the the Eagle furred. You see three
55:01 wars here here and here um And fractures measured from the conductivity of the
55:11 War, extending in a north east west orientation again parallel to the sigma
55:18 . Max. So the induced the hydraulic fractures again follow the same
55:24 as we see in natural fractures with strike of the fractures parallel to this
55:29 that H. Marks. Okay, , so here's a map of the
55:39 basin and each one of these little shows orientation of hydraulic fractures. The
55:51 tend generally northwest southeast, changing slightly more east west than this orientation.
55:59 in this part of the basin, More Northwest Southeast and Central Park and
56:05 east west again in this northern part the basin? So given this information
56:13 what are the what are the strikes sigma one? Sigma three? Sigma
56:18 . Max and sigma H. But here in the here in the
56:22 basin, Sima one is spiral to maximum straight direction. So that is
56:37 west, south east, yep. . Actually my tree is perpendicular to
56:44 , yep. Perfect. And what be the optimum azimuth of well
56:54 What would be the what would be optimum direction of a horizontal? Well
56:58 those stresses. So to and to reservoir or rather to enhance the reservoir
57:08 a jury Franken. They should be the direction of the maximum stress.
57:18 . No, they should be the of the the minimum stress. You
57:23 the Because you want you want the . The fracture is going to form
57:28 this northwest southeast orientation, so they're to open Perpendicular that parallel to Sigma
57:36 . And so the best well orientation be parallel to sigma three,
57:43 southwest. Then you get the most fracture stimulation. Okay, so you
57:54 right about the orientation of the The sigma H. Max is generally
58:00 southeast. Signage man, northeast But to get the the optimum frack
58:09 , you want your well orientation northeast parallel to that sigma one, so
58:14 you open these fractures perpendicular signals, signal one parallel to sigma three.
58:24 that will give you the optimum track . Alright comments or questions on that
58:44 . Right. Um Now the other to recognize is that the orientation of
58:51 and sigma is max varies within Mm hmm. So here's a here's
58:59 map of the the total permian basin the Delaware basin here. The central
59:06 platform here in the midland basin over and here the sigma h. Max
59:15 the area that we're looking tends to on northeast southwest, but south in
59:23 basin, it's more northwest southeast and north south here in the northwestern part
59:29 the basin. So it the orientation over the scale of the basin.
59:37 if you come over to the midland here it's more east west. Then
59:41 see here in the Delaware basin. and a single into max varies regionally
59:49 a basin. And it's important to that into account when you're designing your
59:56 jobs and you're well at your well and all that good stuff.
60:06 Okay. Now interestingly the the impact natural fractures on well performance. What
60:15 see the bottom line is that the fractures don't have any impact on well
60:22 within these hydraulically fractured reservoirs. Yes here I've got a lot of matrix
60:32 versus well test permeability and so that X axis represents the permeability that you
60:41 from an unfree action core plug this test permeability represents the permeability of the
60:49 that you would measure after a Mm hmm. And um each one
60:56 these lines represents an order of magnitude in permeability. So this line 1-1
61:04 where the well test permeability is the as the matrix permeability. Where we
61:11 these naturally fractured reservoirs. You see wealthiest permeability is much higher than the
61:17 permeability by as much as a factor Tend to the 4th, 10,
61:24 , 10 of the 3, 10 the 4th. And hydro fractured reservoirs
61:30 the same trends here we have the low matrix permeability and it's that hydraulic
61:39 that increases the permeability by 1, , 3 or four orders of magnitude
61:44 make these wells economic three And so this, we would expect that the
61:54 fractures would have a positive impact on permeability. That on natural fractures like
62:01 would increase the effective permeability. But in our, even in are really
62:09 reservoirs. And what we found is that's not actually the case.
62:17 So I put this in to emphasize common assumption that these natural fractures would
62:24 expected to enhance the permeability. And is from a paper that we just
62:32 in the bulletin comparing on natural fractures core with production from the wolf camp
62:42 in the Delaware basin. And what found is that these natural fractures just
62:47 have any effect. Don't have any . Try so in in general flow
62:57 proportional to the fracture intensity and that's by this equation where Q Over
63:05 Is the is the flow, it's discharge per unit area. And we
63:10 that that's proportional to E. which is the fracture amateur. Um
63:19 HDL which is the fracture spacing. then um just um gravity density,
63:30 in inversely proportional to the fluid viscosity the and the fracture spacing. So
63:40 we increase the fracture intensity and and the fracture spacing, we should get
63:49 higher flow through these through these rocks on this equation. And so based
63:56 this, we expect more fractured reservoirs have greater flooding. And this is
64:00 we expect natural fractures to have a impact on productivity. But we found
64:11 wasn't the case. What we did look at on natural fractures that we
64:17 in core like this. You can all these natural fractures, some open
64:22 closed your vertical joints in the wolf shale. And we we quantified
64:30 measuring the number of fractures per foot core, from these vertical core.
64:35 that's shown here in this this plot uh where these lines go to the
64:42 show where there's higher fraction intensity or intensity ranges from 1-2 fractures per foot
64:50 much as 10 fractures per foot of . So we we measure these fractures
64:57 prepare this fracture data to the well and what's shown here is a well
65:04 curve with barrels per day as the axis and days on production. Here
65:10 the X axis, the black line the oil production and the blue line
65:18 the water production. And you see initial flow bacteria here with very high
65:25 production and then with time that tails Approaches a constant of around 500 and
65:33 barrels per day of water, The oil also tails off but it
65:39 off at a much lower rate And rate of about 100 barrels per day
65:44 oil. So the water oil ratio these Permian basin wells is just it's
65:53 , very high. You have a amount of water that you have to
65:57 of for the amount of oil produced these wells. So what we did
66:03 compare this fracture data to this well data. Looking at the fracture intensity
66:11 the productivity at these periods where the tails off to a relatively constant
66:25 Alright. And within these, within wolf camp shale here we have multiple
66:29 of fractures. We have the near things, or joints that are
66:38 We have cemented joints like these and we have lots of beef. These
66:44 parallel fracture shown here. So we the total fracture intensity measuring the sum
66:52 all these different fracture types. And of the interesting things is that we
67:03 see any mechanical strategic afi mm And here's an outcrop photo showing on
67:10 well defined mechanical strategic afi where we some fracture spacing that's roughly proportional to
67:17 layer thickness. And it varies from to layer, from that layer to
67:22 fractures in that way. Or more here. More fractures here. Um
67:28 fractures and these ductal layers in And we expected to see some mechanicals
67:33 to you if you like this within chromium. But we didn't we didn't
67:38 that in the wolf camp. We see that in the Permian at
67:44 So, this is Correlation section showing intensity for five different wells within the
67:55 camp in the Premier Basin. And it shows is that between the different
68:03 camp layers, this wolf camp, , B and C. But the
68:09 is is very, but not in consistent way. There's no consistent mechanical
68:16 geography. No one layer is consistently fractured than the other layers or less
68:23 than the other latest. The blanks here represent areas where we did not
68:28 core to measure the fracture. these blanks represent no data zones rather
68:33 no fracture zones, mm hmm. we don't see any consistent mechanicals particularly
68:40 the different wells here. And then is the key plot. This is
68:48 production to the fracture intensity. So , along the X axis, I
68:55 the near vertical total near vertical fractures foot of core. So, I
69:02 everything ranging from zero to about two fractures per foot of core, on
69:08 y axis here we have barrels per when water production shown here in the
69:15 oil production shown here in the black these represent the production rates at those
69:23 That we get after 100 and 200 300 days of production. Sure.
69:27 there's just there's no correlation of the productivity or the water productivity and barrels
69:35 day versus the fracture intensity. These are relatively constant regardless of the natural
69:44 intensity. So, we have we kind of a conundrum here.
69:51 We expected these natural fractures to increase fracture intensity and increase the well
69:59 And what we're seeing is that that's not the case at all. So
70:05 we were able to look at a through a hydro fracked rock volume and
70:17 induced fractures, hydraulic fractures from natural . And they're they're pretty easily distinguished
70:26 the hydraulic fractures. First of you don't have any cement.
70:29 the natural fractures are easily distinguished by . Fine. The induced fractures have
70:36 steps that you don't see your natural . And you have these highly irregular
70:43 that you don't see in natural You don't see any of the promos
70:47 structures we were seeing in the joints the natural joints previously. And you
70:53 these curious little ovoid features on the of the induced tractors. Okay.
71:01 from the hydraulic stimulation. So from core, we could distinguish the hydraulic
71:09 intensity versus the natural fracture intensity. can't. And the results are shown
71:18 . We're on the top. I a schematic showing the collateral well bored
71:25 we were able to measure the fractures this world war at a high orientation
71:31 the world war. And these are results here. This the X axis
71:37 the is the measured depth along the the y axis. Here is the
71:44 intensity plotted in fractures per foot of . And there are there are two
71:51 of natural fractures, the brown and green here. And they they show
71:58 here along the along the X axis very, very low values we
72:06 We basically have 0-1 natural fracture per of core. Some exceptional highs as
72:15 as three fractures per foot of but typically 1 - two. Typose
72:23 natural fracture or less per foot of . The blue shows the hydraulic fractures
72:31 what this shows is that the hydraulic intensity is much greater than the natural
72:37 intensity. Overall the natural fractures average fractures per foot of core, Whereas
72:46 hydraulic fractures average twice that .35 fractures before. So the hydraulic fracture intensity
72:54 much greater in the natural fracture intensity that we concluded that that hydraulic fracture
73:02 just totally overwhelmed the natural fractures. these when you produce from these,
73:09 production is totally controlled by the hydraulic intensity and the natural fractures are such
73:16 low intensity compared to that, that really don't affect the flow at
73:25 Any any comments or questions on that , sir. So on. This
73:37 regarding how the Adriatic fractures fractures are more productive in water and soil productivity
73:46 the natural fractures. So I'm thinking my head that due to these natural
73:52 being way higher in depth and these fractures were formed in time. So
73:59 have gone through the effect of being and being cemented. So I'm thinking
74:06 compaction and segmentation of their jury fractures the natural fractures. Is this why
74:13 are less productive even though they are more or they might be. So
74:21 thinking if compaction and sanitation, which just the productivity of the natural
74:30 Yeah, we don't we don't think because the um the cemented natural fractures
74:37 popped open by this hydraulic stimulation. like the just like the hydraulic
74:45 So after the after you pumped down frack job, you pumped down the
74:50 in the profit that opens both new and the natural fractures. So we
74:57 that semente shin doesn't have any impact the productivity of the natural fractures in
75:04 wells. When we looked at this , we could see profit in both
75:11 natural fractures and the induced fractures. we think the natural fractures are popped
75:18 , just like the hydraulic fractures, that's that was a good question.
75:38 , any other comments or questions? , to summarize this section, we
75:57 about the three generic types of The Mode one. Mode 2.
76:03 the mode three Or the mode are the tensile fractures. These are
76:08 joints of the bed, parallel The beef with no fracture parallel
76:14 The modes two and 3 have a parallel tooth fracture plane so there.
76:21 they're sure fractures rather than tensile The tensile fractures required high fluid pressures
76:30 although deviate oryx stress alot on diameter that stress circle too. Get into
76:36 tensile fracture realm of budding relationships with joints. Give us the relative
76:44 not the fractures. The promos features we see on the fractured surfaces give
76:51 the fracture propagation direction, the joint direction. Well, the most important
76:58 is that the joint strike is parallel the strike of cigna H.
77:03 So we can use that joint strike tell what the stress orientations were at
77:08 time of joint formation. Both the and the bed parallel fractures require high
77:15 pressure. We need that high fluid to move the stress circle into the
77:21 failure realm. On the more cruel failures diagrams. Bed parallel fractures require
77:30 pressure approximately equal to the overburden. fluid pressure has to basically lift up
77:36 overburden to generate those bed parallel And we can we can calculate what
77:43 fluid pressure has to be just based the depth of the fracture formation?
77:49 hmm. Many joints formed during like we saw in the in the
77:57 and in the eagle furred the joints we see an outcrop are not necessarily
78:04 same as those presidents subsurface. And consequence of these joints forming turing
78:12 So, some of the joints of maximum or some of the joints are
78:19 present at maximum burial, the only during uplift. So, there's a
78:23 between what we see at the surface what we see in the subsurface and
78:30 fresh and reservoirs. The intensity of hydro fractures is much greater than the
78:36 of the natural fractures. And The result is that the intensity of
78:43 fractures really has no effect on well in hydraulically fractured reservoirs. Mhm,
78:59 hmm. All right. So, concludes the section on geo mechanics,
79:04 hmm. Are there any comments or ? More questions on this? Mm
79:27 . Okay. Alright. So, got we got through this much quicker
79:34 I anticipated. Mhm. So, I scheduled next was a a lunch
79:41 and then we'll go on this afternoon talk about top seal failure. I
79:46 , this will take a lot of things that we talked about and learning
79:50 mechanics and fracture section and will apply to topsail failure. No. And
79:57 don't we take a break? And start this again at 12:30 PM.
80:03 that does that work for you? that? Okay, so we'll take
80:23 break here and we'll pick it up at 12:30 PM. Okay.
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