THE SHALE EVOLUTION:
`Zipper Fracture Takes Hold
`
`Trent Jacobs, JPT Technology Writer
`
`Downloaded from http://onepetro.org/JPT/article-pdf/66/10/60/2212149/spe-1014-0060-jpt.pdf/1 by Robert Durham on 12 August 2022
`
`A Halliburton crew performs a zipper-fracturing completion
`on three horizontal wells in the Eagle Ford shale of south
`Texas. The multiwell completion technique has been rapidly
`adopted by the unconventional industry as operators realize
`time savings and production benefits from stimulating more
`reservoir rock. Photo courtesy of Halliburton.
`
`Ahorizontal well completion method known as
`
`zipper fracturing has been rapidly adopted over
`the last couple of years by companies in the Eagle
`Ford shale of south Texas. Instead of drilling and hydraulically
`fracturing one well at a time, the zipper method involves
`drilling multiple wells from a pad site and then hydraulically
`fracturing a stage in one well, while getting ready for the
`next, as wireline and perforation operations take place in
`another. The multiwell completion method earns its name
`from the zipper-like configuration of the fracture stages
`from wells drilled with relatively tight spacing.
`This shaves days off the time it takes to complete
`a multiwell pad. Many companies in south Texas are
`now using the completion method on almost every new
`pad site they drill into, saving tens of millions of dollars
`per year while accelerating the development of their
`well inventories.
`But the big prize may be that zipper fractures are
`increasing initial production and estimated ultimate recovery
`rates when designed so that the fractures stimulate the
`
`most reservoir volume possible. Tulsa-based WPX Energy, an
`independent operator of 160,000 acres in the San Juan Basin
`of New Mexico, told investors this summer that when the
`company switched to zipper fracturing, it averaged 420 B/D
`of oil production compared with 388 B/D from single-well
`completions. While not entirely sure if zipper fracturing is
`the direct cause of improved production, WPX said it expects
`that is the case.
`Mukul Sharma, a professor and chair in the petroleum
`department at the University of Texas at Austin (UT), said
`field data from Eagle Ford wells make it clear to him that
`zipper fractures are indeed improving initial production rates
`and the estimated ultimate recovery. Sharma said operators
`in south Texas have reported improved initial production
`rates ranging from 20% to 40% using the zipper method. “I
`would say that this is definitely the way people are going to
`be doing a lot of their fractures in the future,” he said. “What
`I think we need to do is understand better how it works—
`why it works. Once we understand that, we can apply it much
`more efficiently.”
`
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`61
`
`Marathon Oil first tested the zipper method in the Eagle
`Ford shale 2 years ago. Today, at least 95% of the company’s
`pad wells are being completed with zipper fractures. This is
`saving Marathon an average of 4 days in completion time per
`pad. “Anything with two or more wells, we will zipper frac,”
`said Richie Catlett, completions engineering supervisor at
`Marathon. “From a completions standpoint, for us the main
`thing is efficiency. It cuts days off our operations, and that is
`the big reason we went to zipper fracs.”
`The Eagle Ford is also where Schlumberger is doing
`its highest share of zipper fractures, but the company
`said there is significant momentum behind its adoption
`outside south Texas, including in the Permian Basin of west
`Texas and Williston basin in North Dakota. “Nearly half of
`the completions that we do today in North America are
`completed with what we call the zipper-fracturing method,”
`said Alejandro Peña, global chemistry and materials portfolio
`manager at Schlumberger.
`As the use of this method spreads, the Eagle Ford
`shale remains the uncontested zipper-fracturing capital
`of the world. Two-and-a-half years ago, less than 25% of
`Halliburton’s completion operations in the Eagle Ford were
`zipper fractures. Since then, that share has grown to 85%.
`Bill Melton, a completions sales manager at Halliburton,
`said operators have been inspired to adopt the method
`more for its completion efficiencies than for its potential
`production benefits.
`“By doing zipper fracs,” he said, “a customer can do six
`to eight frac stages a day. Whereas if they did each well for
`the entire length, and then switched over to the next well,
`they could only do three-and-a-half to four stages a day.”
`Halliburton has even taken the zipper method south
`of the US border into Mexico for Petróleos Mexicanos, more
`commonly known as Pemex, where unconventional shale
`exploration remains in its infancy. The company believes
`that this could help develop Mexican shale fields, and those
`elsewhere, relatively quickly compared with the Texas
`experience, which took years of trial and error to achieve
`the near-record production levels seen today. “It takes
`advantage of all the learning that has already been done, and
`it accelerates their development cycle time,” Melton said.
`“Where it may have taken a year for a US operator to get
`to a 50-well volume, if they are doing pad drilling and pad
`completions,” non-US operators could be there in a third of
`the time.
`
`Changes and Challenges
`Companies using the zipper method have had to make a few
`operational considerations that do not apply to single-well
`completions. When completing horizontal wells one at a
`time, once the fracturing job in an individual stage is finished,
`the wireline operation to set plugs and perforate the next
`stage in the wellbore normally takes 2 to 3 hours, though it
`can last for as long as 5 hours between stages.
`
`JPT • OCTOBER 2014
`
`Clifford Phillips, an advanced drilling engineer at
`Marathon, said when doing zipper fracturing the break
`in stimulation operations may only last 15 minutes as
`workers switch from one well to another. “It is a big change
`operationally for the frac crew,” he said. “They go from
`having a huge amount of dead time in between fracs to
`almost no time at all.”
`The constant rate of high-horsepower pumping has a
`downside for service companies; their pumping trucks are
`lasting about half as long when working on zipper fractures.
`Catlett also said zipper fracturing allows service companies
`fewer opportunities to perform maintenance on in-between
`jobs. “They have to either provide more pumps, which is
`getting to be a problem with the industry right now, or they
`are going to have to provide more efficient pumps that can
`last longer,” he said. “It is a challenge.”
`With a lot of the extra workload shouldered by the
`service companies, one challenge for the operator is to make
`sure that a steady stream of sand or proppant is arriving
`to the pad site to keep up with the continuous fracturing.
`Marathon engineers said they like to keep enough proppant
`on site for at least four or five stages so that if there is
`an interruption in deliveries, the fracturing crew can keep
`moving, which increases truck traffic into and out of the pad
`site substantially.
`There are some limitations to deploying the zipper
`method. On a five-well pad Marathon will only zipper fracture
`three wells at a time, and then the next two. This is because
`the crane it uses for the wireline operations only has a radius
`of 90 ft while the wells are spaced out at approximately 25 ft
`to 30 ft.
`In terms of extra equipment, the only added system
`requirement is what is called a zipper manifold, which Dennis
`Donovan, completions engineer at Marathon, described as a
`“frac stack” turned on its side that redirects the fracturing
`
`n D... ~ J_
`I
`.-
`-
`l_T
`I 1-T
`-
`I
`J__
`I
`
`Texas Two Step
`
`Conventional
`
`;
`
`;
`
`MZF
`
`Zipper Frac
`
`I -
`-
`I -
`-
`1-
`1 -
`
`As seen from above, the various types of completion
`methods that are used to develop shale formations. The
`modified zipper fracturing (MZF) is the latest evolutionary
`step taken by the industry to yield more production
`compared with the regular zipper fracturing and “Texas
`Two Step,” also known as alternating fracturing, where
`stages are stimulated out of sequence. Image courtesy
`of Mohamed Soliman/Texas Tech University.
`
`IWS EXHIBIT 1037
`
`EX_1037_002
`
`

`

`ZIPPER FRACTURES
`
`Downloaded from http://onepetro.org/JPT/article-pdf/66/10/60/2212149/spe-1014-0060-jpt.pdf/1 by Robert Durham on 12 August 2022
`
`A closer view of a Halliburton zipper-fracturing treatment shows the tight arrangement of pressure pumping trucks,
`wellheads, and wireline crane. The company said that in less than 3 years, the proportion of zipper-fracturing
`completions it does in the Eagle Ford shale of Texas has increased threefold to 85%. Photo courtesy of Halliburton.
`
`fluids into different wells. “That way we are going down the
`line from one well to the next,” he said. And the cost of the
`manifold is easily offset by the money saved in rig time and
`other rental equipment.
`
`Time Delay Critical
`When hydraulic fractures propagate into a formation, a
`stress shadow is created inside the rock that acts like a
`force field, hindering the fracturing of another stage. As the
`fracture closes, the spatial extent and the magnitude of the
`stress shadow is reduced.
`Sharma has been studying the role that induced
`unpropped fractures play in unconventional development
`for years and has found evidence suggesting that they
`not only exist, which has been a subject of debate, but
`they also penetrate into the rock farther than the propped
`fractures do. He said production history matching, tracer
`technology, and microseismic monitoring all indicate
`that induced unpropped fractures tend to form around
`
`the propped fractures and then close in a relatively short
`period of time.
`This is important because Sharma believes it is the
`reason why zipper fractures work. “The stress shadow
`you see right after you frac the well can have a fairly large
`spatial extent, but over time this stress shadow will become
`confined to a region around the main fracture as the induced
`unpropped fractures close,” he said.
`Allowing the stress shadow to shrink is believed
`to make fracturing the subsequent stage in a horizontal
`well more effective because there will be far less stress
`interference in the rock from the previous fracture blocking
`the new fractures.
`When hydraulic fractures are closely spaced, the stress
`shadow effect can lead the fractures to grow away from one
`another and towards areas of lower stress, which may mean
`less rock is stimulated. To reduce the effect of the stress
`shadow, Sharma said some operators are doing four-well
`zipper fracturing instead of two-well.
`
`62
`
`JPT • OCTOBER 2014
`
`IWS EXHIBIT 1037
`
`EX_1037_003
`
`

`

`ZIPPER FRACTURES
`.....................................................................................................................................................................
`
`A3
`
`A2
`
`A1
`
`Downloaded from http://onepetro.org/JPT/article-pdf/66/10/60/2212149/spe-1014-0060-jpt.pdf/1 by Robert Durham on 12 August 2022
`
`Safety ConSiderationS
`
`From the service company’s perspective, Halliburton
`said that the technical hurdles to move from a single-
`well completion to a multiwell completion, such as in zip-
`per fracturing, are not all that high. Although, the fast-
`paced operations, extra equipment, and personnel do
`increase the level of planning needed for a zipper frac-
`turing. “It is really a tremendous exercise in collabora-
`tion and optimization to pull some of these very massive
`jobs off at a very intense rate,” Bill Melton, a completions
`sales manager at Halliburton, said.
`Regarding safety, there are other considerations
`to make as well. One involves preventing a radio signal
`from errantly inducing an electrical current that might
`prematurely fire one of the perforating guns used to
`punch through the casing and into the formation using
`an explosive shape charge. Halliburton developed its own
`radio-safe detonators and perforation guns to minimize
`the risk of an accidental detonation. In a zipper fracture,
`there are multiple guns that might go off because of an
`errant radio signal.
`Clifford Phillips, an advanced drilling engineer at
`Marathon, said the company has also implemented its
`own safety practices at its pad sites to protect workers.
`After testing the zipper method, the company realized
`that it could be done safely but it wanted workers to pay
`even closer attention to the increased number of high-
`pressure lines to ensure that they are not near people
`while they are working. “You have to make sure that the
`wireline guys who are working together with the frac
`guys are never around each other when there is pressure
`in the lines,” he said.
`
`“It is those three issues combined that we think are the
`foundational and important issues when zipper fracs work,”
`he said. “When they do not work, one of those three things is
`essentially missing.”
`Without natural fractures, Nagel believes that zipper
`fractures will have zero impact on production. He said one of
`the reasons that the zipper-fracturing method has taken off
`in the Eagle Ford shale more than in other areas is because
`of the prevalence of natural fractures. Unlike in the Barnett,
`Bakken, Marcellus, and Haynesville shales, operators in the
`Eagle Ford have reported more pressure communication
`between adjacent wells. This suggests that natural fractures
`in the Eagle Ford tend to exhibit greater communication over
`a longer range than in many other shale plays.
`“For those situations like the Marcellus and
`Haynesville, where it is very uncommon to see operators
`report pressure communication between wells—that tells
`you the natural fracture system is not as pervasive or not as
`connected,” Nagel said. “That would mean that you are not
`
`B2
`
`B1
`
`This example shows zipper-fracturing treatments for two
`wells in the sequence of A1, B1, A2, B2, A3, and so on.
`Image courtesy of Petróleos Mexicanos.
`
`“You can do Well 1, then 4, come back and do 2, and then
`do Well 3,” he said. “People have tried that and it seems to
`work.” By applying the method to four wells instead of just two,
`Sharma said the time delay between two adjacent fractures in
`the wellbore can be extended by a factor of five or six.
`One way operators can plan and design for this is by
`using modeling software that includes the stress shadow
`effect from adjacent wells. In the past, most commercially
`available fracturing software modeled one well at a time. Over
`the past 2 years, Sharma said companies have realized that
`modeling horizontal well fractures in isolation is insufficient
`when planning for a zipper-fracturing program. As a result,
`UT now offers operators software that is able to model more
`than 100 fracturing stages in a multiwell pad.
`
`Zipper Mechanics
`Neal Nagel, chief engineer and principal at Houston-based
`OilField Geomechanics, started studying zipper fractures
`several years ago when operators needed help in figuring
`out why the completion method has increased production
`for some, but not for others. He said the big question that
`operators want to know is why does the interaction between
`two wells potentially increase production?
`“There is a strong link between a hydraulic fracture and
`the natural fractures, and from a geomechanical perspective,
`we were looking at that,” he said. Using a series of numerical
`tools, called discrete element models, Nagel simulated and
`evaluated the interaction of hydraulic fracturing with natural
`fractures. Instead of doing this with a single horizontal well,
`the simulation was run with a dual-well configuration. What
`Nagel concluded from his geomechanical evaluations is that
`there are three primary factors that dictate how well a zipper
`fracture may perform. They are:
`◗ Existence and conductivity of the natural fractures
`◗ The impact the stress shadow may have on hydraulic
`fracturing between two wells
`◗ Ability to change the pressure within the natural
`fractures between two wells
`
`64
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`JPT • OCTOBER 2014
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`EX_1037_004
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`

`
`
`Borehole
`Geophone
`Array
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`
`65
`
`The image on the left shows the position of microseismic geophones and on the right are the microseismic events
`recorded during a zipper-fracturing sequence. Image courtesy of Research Partnership to Secure Energy for America,
`and Gas Technology Institute.
`
`to slip; we see greater microseismicity, we see increase in
`flow capacity, and we see an increase in production.”
`
`Modified Zipper Fracture
`Before Mohamed Soliman became the chair at Texas
`Tech University’s petroleum engineering department in
`2011, he worked for Halliburton for 32 years and holds
`26 patents on hydraulic-fracturing technology. One of
`the patents that Soliman received while at the company
`was for the alternating fracturing, a precursor to the
`more efficient modified zipper fracture, which also was
`designed to breakup as much rock to create more complex
`fracture networks.
`“We came up with alternating fracturing which is done
`from one well. You create a fracture, then you create another
`
`Modified
`Zipper Frac
`Zipper Frac
`
`7.0
`
`6.0
`
`5.0
`
`4.0
`
`3.0
`
`2.0
`
`1.0
`
`0.0
`
`Total ProducƟon (Bcf)
`
`0
`
`500
`
`1,000
`Time (Days)
`
`1,500
`
`2,000
`
`Simulation results of two wells show the modified zipper
`fracture (MZF) increasing gas production by 44% more
`than the original zipper fracture due to the increased
`fracture complexity. Graph courtesy of Mohamed Soliman/
`Texas Tech University.
`
`going to be able to change the pressure between two wells.
`And without that pressure change, a zipper frac is unlikely to
`show much benefit.”
`Also, to achieve a positive production outcome, the
`wells must be properly spaced, and the fractures need to
`be long enough so that they touch and overlap with one
`another, thus ensuring there is communication between
`adjacent wells.
`An SPE paper published by Halliburton this year, which
`evaluated the benefit of zipper fractures in unconventional
`reservoirs ran simulations that showed when zipper
`fractures overlap the incremental recovery factor was in
`the range of 15% to 20%, compared with zipper fractures
`that do not overlap.
`Based on the field data and case study work he has
`done, Nagel is convinced that pore pressure is the most
`important factor leading to a zipper fracture that nets higher
`stimulated reservoir volume and thus production. “When
`I create a hydraulic fracture, I am injecting at a pressure
`higher than the minimum in-situ stress, which, by definition,
`has to be greater than my pore pressure,” he said.
`The effect of the increased pore pressure is that
`the natural fractures are induced to slip more, thereby
`increasing the permeability and flow capacity of the source
`rock, as Nagel’s research suggests, and is responsible for
`the higher productivity in zipper-fractured wells. He said
`these subsurface events can be detected and observed using
`microseismic technology.
`“When zipper fracs work, we have a configuration
`where the pressure increase from the first well increases the
`pressure in the region of the second well,” Nagel said. “When
`we frac that second well, what it (increased pressure) does is
`make it easier for the natural fractures and weakness planes
`
`JPT • OCTOBER 2014
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`IWS EXHIBIT 1037
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`EX_1037_005
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`Downloaded from http://onepetro.org/JPT/article-pdf/66/10/60/2212149/spe-1014-0060-jpt.pdf/1 by Robert Durham on 12 August 2022
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`ZIPPER FRACTURES
`
`Diversion Technology complemenTs Zipper FracTures
`
`A primary driver behind the adoption of zipper fractures
`has been to reduce the money and time spent complet-
`ing a series of wells. Service companies such as Schlum-
`berger are now incorporating ancillary technologies, such
`as diverting agents to boost the efficiency of zipper frac-
`tures even more. The fracturing technology is called Broad-
`Band Sequence by Schlumberger, and involves a divert-
`ing agent made of biodegradable composite particles and
`fibers, and is also used in refracturing operations where it
`is difficult or impossible to re-enter an older well to set and
`remove plugs.
`In most fracturing operations, be they multiwell or
`single-well, mechanical devices such as bridge plugs are
`used to isolate each stage so that the hydraulic pres-
`sure flows into the targeted interval. The process is con-
`tinued systematically along the length of a horizontal well.
`By using a diverting agent operators save several trips in
`and out of the well with wireline and coiled tubing units
`to set and then mill out the plugs. Other service compa-
`nies, including Weatherford, Halliburton, and Baker Hughes
`have also developed their own diversion fluids for stimula-
`tion operations.
`In addition to saving on completion time, Schlumberg-
`er touts its ability to help improve oil and gas production by
`increasing the reservoir contact of the stimulation opera-
`tion. This year Marathon and Schlumberger co-authored
`an SPE technical paper detailing a case study of a zipper-
`fracturing operation in the Eagle Ford shale, which showed
`the incorporation of a diverting agent improved production
`by about 20% compared with an adjacent well that used the
`same completion parameters, minus the use of the Broad-
`Band Sequence technique. Alejandro Peña, global chemistry
`and materials portfolio manager at Schlumberger, said that
`
`Designed to increase the effectiveness of hydraulic
`fracturing, Schlumberger’s biodegradable composite
`diverting agent is one technology that has the ability
`to further improve the efficiency of zipper fractures.
`Image courtesy of Schlumberger.
`
`the net production gain seen in the case study is an average
`result for horizontal completions.
`When using its newly commercialized technology, the
`company follows a prescribed workflow to assess how much
`composite material is needed and then the crew pumps it
`downhole. “We have at the wellsite a dedicated pump, which
`connects at the discharge of the fracturing fleet before you
`enter the wellbore,” said Peña. “We inject the (compos-
`ite material) right at the end of the fracturing treatment to
`basically provide temporary isolation in the fractures that
`have just been stimulated.”
`The company introduced BroadBand Sequence in Feb-
`ruary and reported that the proportion of completions that
`it is used in is already in the “double digits.” It did not pro-
`vide a figure.
`
`fracture, and then you go in the middle to create another
`fracture,” he said. “Needless to say, operationally this is not
`exactly what you would want to do.”
`Soliman explained that technology has been created to
`lessen the complications involved with fracturing stages out
`of sequence but there are too many operational complexities
`to work through. “It can be done, but it is a headache,”
`he said.
`When Soliman got to Texas Tech he and his research
`students took a look back at alternating fracturing and also
`the emerging zipper-fracture method to see if there was
`a way to net similar production results from alternating
`fracturing, but without the operational complexity.
`What they ended up inventing was the modified zipper
`fracture that differs from a normal zipper fracture. Rather
`than having the fractures of two adjacent wells pointing
`
`toward one another, they are staggered so the fractures will
`overlap with one another. Soliman said that with the modified
`zipper fracturing operators get the benefits of alternating
`fracturing without all the extra work.
`“You probably will have to have your horizontal wells
`a little closer than you would have in a regular zipper frac,
`or you create a fracture that is a little longer,” he said.
`“Another issue is that it will require more engineering work
`ahead of the drilling. You need to acquire some data, and do
`your homework.”
`Soliman said he and a graduate student have created a
`simulation software to further study fracture attraction. The
`software has not yet been commercialized but Soliman said
`he expects to present it at future SPE conferences.
`One of the most intriguing aspects of the
`overlapping fractures that Soliman has observed is that
`
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`67
`
`Change in Shear Stress (MPa)
`
`–100
`
`–50
`
`0
`
`50
`
`100
`
`150
`
`3
`
`2
`
`1
`
`0
`
`–1
`
`–2
`
`–3
`
`25 µm
`
`Microcrack
`in Glass
`
`A vein in
`granite rock
`
`250 m
`
`Minette dike
`
`Mancos Shale
`
`Quartz=Feldspar vein
`
`2 7 0 0
`
`2 7 0 0
`
`A dike
`
`Overlapping
`spreading
`centers
`
`2700
`
`Granitic Rock
`
`25 cm
`
`12˚54’N OSC
`
`T
`
`2.5 km
`
`
`
`150
`
`100
`
`50
`
`0
`
`–50
`
`Distance Along Wellbore (m)
`
`–100
`
`–150
`–150
`
`To verify their fracture model (left), which showed that as two fractures propagate towards one another they begin to
`demonstrate a physical attraction, researchers from Texas Tech University looked for other examples and found that the
`phenomenon is ubiquitous in the natural world. Image courtesy of Mohamed Soliman/Texas Tech University.
`
`as the fractures propagate towards one another, once
`they are in very close proximity, they begin to show an
`attraction. Soliman said he has recently completed research
`work on this phenomenon and will publish the results later
`this year.
`
`“If you have fractures coming fairly close to one
`another, they will actually turn around towards each other,”
`he said. “It is very interesting. It looks almost as if it does not
`make sense, but when you think about the calculations of
`how stresses change—it does.” JPT
`
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`JPT • OCTOBER 2014
`
`IWS EXHIBIT 1037
`
`EX_1037_007
`
`