Jspa ..
`_ International
`
`Society of Petroleum Engineers
`
`SPE 106357
`
`Effective Stimulation of Horizontal Wells - A New Completion Method
`Rocky Seale, Packers Plus Energy Services; Dan Themig, Packers Plus Energy Services; James Athans, Packers Plus
`Energy Services
`
`This paper was prepared for presentation at the 2006 SPE Tedinical Symposium of Saudi
`Arabia Section held in Dhahran, Saudi Arabia, 21-23 May 2[)U6
`Copyright 2006 Society of Petroleum Engineers
`This paper was selected tur presentation by the Technical Symposium Program Ccimmittee
`following review at
`infonnanon contained in full manuscript submitted by the autnorts).
`Contents at the paper, as presented, have not been reviewed by the Society at Petroleum
`Engineers and are subjecttn correction by the aulhorts}. The material. as presented. does not
`necasarily rellect any position of the Society at Petroleum Engineers, its ofiicers. or members.
`
`Abstract
`Over the last several years there have been many
`developments in horizontal completions. Thcsc advancements
`have been designed to better stimulate the entire horizontal
`interval. The most notable advancement has been used in
`
`cased and cemented liner applications, where composite plugs
`have provided the mechanical diversion that has successfully
`stimulated the entire horizontal wcllborc.
`llowcvcr, the
`process of setting a plug on coiled tubing (Cf), perforating,
`stimulating and then repeating the process for the required
`number of stages to optimize production and then running
`back in with C1‘ to remove the plugs is costly and time
`prohibitive in many cases. In open hole applications,
`horizontal stimulations have relied almost solely on limited
`entry or bullhcading in attempts to induce multiple fractures.
`This method has provcn very inefficient and unsuccessful.
`
`A new completion system has been developed that addresses
`all ofthe prior issues in stimulating horizontal wells. This
`system uses a series of mechanical open hole packers
`deployed on the production liner with fracturing or stimulation
`ports located between the packers that allow for stimulation in
`each desired interval. Without the requirement of cementing
`the liner in place, all the problems associated with cementing
`are eliminated. By placing a liner in the open hole section
`rather than leaving it barefoot, accessability and production
`issues are more easily addressed. Additionally, the
`mechanical packers provide mechanical diversion at high
`differential pressures. The system has also been designed, so
`all of the fracturing or stimulation treatments along tl1c
`horizontal wcllborc can be pumped in one continuous
`operation, thus minimizing all the associated risks and
`optimizing the efficiencies for both the personnel and
`equipment. With hundreds of jobs completed, this paper will
`detail the operational efficiencies and reliability of this
`completion system, as well as analyze the cost benefits and
`production increases that have been noted.
`
`Introduction
`Horizontal drilling has been steadily growing for well over a
`decade and in many cases has become the exploitation method
`of choice for infill drilling and reservoir depletion. As
`successful as horizontal drilling has been, there have been
`significant technology gaps hampering growth in certain
`applications. These are applications where fracturing or
`stimulating the reservoir is necessary to proliferate production
`to desired levels. For cased and cemented liner applications
`this issue was addressed some years back by the use of bridge
`plugs set on coiled tubing (CT) to establish mechanical
`diversion, followed by perforating and then stimulating the
`well as designed. The process is then repeated for the number
`of stimulations desired for the horizontal wcllborc. After all
`the stages have been completed, CT is utilized to drill out the
`composite plugs to establish accessability along the
`horizontal.‘ This process has been effective for some
`applications, however, the inherent cost and time of multiple
`interventions with CT, perforating guns and stimulation
`equipment needed lbr each stage, coupled with the mechanical
`risks of setting and removing the composite plugs has been
`prohibitive in many cases. This problem is only exacerbated
`at higher temperatures and pressures, with additional exposure
`created to personnel and equipment. Further to these
`developments for cased and cemented applications has been
`the use of external perforating in recent years. This
`development has allowed multiple fractures to be placed into
`the wcllborc without the costly intervention, however, the
`geometric considerations of the equipment are sometimes
`limiting?
`
`The other method for completing horizontal wells is open
`hole, either using a barefoot completion or running slotted or
`perforated liner. Both completion designs provide limited
`flexibility in stimulation and well control. Stimulations for
`both completions can either be done by limited entry or by CT
`washing] However, CT access is limited in many barefoot
`completions due to the friction buildup in the open hole. This
`prevents the CT from reaching the toe of the horizontal
`wellborc in many cases and also any possibility of stimulation
`beyond where the CT can reach.
`In perforated or slotted liner
`completions the CT has the ability to reach further into the
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`Exhibit 2003
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`horizontal section for stimulation, but water or gas shut-off in
`these completion designs becomes a major obstacle, ofien
`leading to premature abandonment. Evaluating the economic
`loss is hard to quantify, but there are many things to consider.
`1’irst, there is the cost of drilling the section of the horizontal
`wellbore that may contributed little or no production. Then
`there is the lost production from that section of the reservoir
`that was drilled, but did not produce. During the life of the
`well there are often attempts to stimulate or remediate based
`on particular problems encountered. All these have a
`cumulative cost affect.
`
`There have been attempts to develop better techniques for
`accessing and stimulating horizontal wells. In open hole
`applications chemical diversion has been developed.3
`Chemical diversion has been effective in certain instances, but
`the need for mechanical diversion in open hole horizontal
`wells was evident. Further evidence of the need for
`
`mechanical diversion has been provided by the 1nicro—seis1nie
`data obtained during horizontal limited entry trcatrncnts.” It
`was for this reason that in 2000 the development of open hole
`mechanical diversion was placed at the forefront of research
`and development. Over the next two years various product
`components and systems were tested and deployed in the field.
`These tests led to what is now the standard system for both
`carbonate and sandstone completions, with more than 200
`successful runs to date.
`
`By developing a system that would set in open hole, provide
`mechanical diversion and allow multiple stirnulations or
`fractures to be performed along the entire horizontal wellbore,
`it would address the problems associated with open hole
`completions to date. What was developed was a mechanical
`open hole packer system capable of withstanding high
`differential pressures, with specially designed fracturing or
`stimulation ports that would be located between the packers.
`A series of these could he run simultaneously in the well on a
`liner and the fractures or stimulations could be pumped in
`succession. This system eliminates the problems often
`encountered when cementing horizontal liners in place, while
`also eliminating the need for repeated CT intervention into the
`well for setting bridge plugs and running perforating guns, and
`the repeated rigging up and down of the fracturing or
`stimulation equipment. The system provides the equipment he
`rigged up and down only one time, thus saving time, money
`and reducing the health, safety and environment (I ISE)
`hazards associated with those activities. This system has
`significantly increased the applications where horizontal
`drilling is viable by lowered the completion and operation
`costs and increasing production.
`
`System Developments
`In 2001, it became apparent that there were significant
`deficiencies for diversion in open hole horizontal wells.
`also apparent, that ifa system could be developed, the
`applications for horizontal drilling would expand
`exponentially. A product development initiative was
`undertaken to develop a system for open hole mechanical
`
`It was
`
`diversion that could withstand the high pressure environments
`of fracturing and stimulating.
`
`Through extensive testing and past history, the use of
`inflatable packers was determined to not be a plausible
`product for the application for several reasons. First,
`inflatable packers could not withstand the high differential
`fracturing and stimulating pressures noted in the vast majority
`of horizontal drilling applications or potential applications.
`Second, was the issue of cooling the inllation fluid down
`during the pumping oflhe job, which decreased the inflate
`pressure, thus further reducing the differential capabilities of
`the tool. Armed with these results and experiences,
`development began on a more robust system that would be
`capable of holding 10,000 psi differential treating pressures
`for long durations. The results of those developments are as
`follows.
`
`It was obvious if an inflatable packer would not suffice, a
`mechanical too] would be required. Various mechanical
`designs were evaluated that would adhere to the operational
`requirements set forth. These requirements were established
`after a thorough review of horizontal applications and
`corresponding performance criteria therein. The packer would
`be required to sustain differential pressure ratings of 10,000
`psi at temperatures up to 400017 and set in holes enlarged up to
`30%. Further operational considerations while evaluating
`liner running procedures, determined that mechanically setting
`the packers would not be viable due to the required
`manipulation of the liner string. Through this initial
`evaluation it was concluded that hydraulic setting for the
`mechanical packers with mechanical retention would be the
`optimal solution. Based on input from various customers a
`dual element system was employed. This provides a
`redundant seal over a specified length in the event the fracture
`or stimulation were to propagate horizontally, the packer could
`retain mechanical diversion within the section length.
`
`Although the design of the open hole packer was crucial,
`development of the fluid placement method between the
`packers was equally critical. Two systems resulted from these
`developments, one designed for carbonate stimulation and the
`second for sandstone fracturing.
`ljach of these presented
`unique challenges. The fracturing system had to be designed
`to selectively open at specific times and once open withstand
`the abrasive fracturing fluids for extended periods of time.
`Initial designs for the fracturing port provided for the optimum
`flow area in conjunction with the system, while maintaining
`the desired tensile and compressive strengths. For example, in
`a 6" hole, the standard completion is 4-1/2", so the mechanical
`properties of the fracturing port were designed to exceed 4-
`1;‘ " ll.60 ppfP-1 10 liner. This provided a greater inflow
`area than the cross section of that same liner, thus not inducing
`a pressure drop through the completion. Initiation of the
`fracturing port was designed to be accomplished with balls
`that could be dropped from surface during the pumping
`operation. After dropping the ball, it could be pumped down
`in the flushing fluid of the previous fracturing interval and
`land in a specific seat to activate that fracturing port for the
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`Exhibit 2003
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`next interval and provide a seal on the seat to prevent treating
`the intervals below. Development of the ball seats was also
`challenging. The seats for the last stages of the system would
`be exposed to the majority of the proppant pumped inducing
`abrasion and erosional effects. Extensive engineering design
`and testing went into establishing, not only the geometry of
`the seat, but the proprietary material specifications for the seat.
`At the conclusion ofthe laboratory and field tests, the seats
`exhibited superior wear resistance to the fracturing lluid
`erosional and abrasion effects. The halls and seats were then
`
`sized to allow for the process to be repeated a number of
`times. Through the above mentioned laboratory and field
`testing, the balls and seats have evolved to their present
`configuration allowing eight ditferent size balls to be dropped
`in the 4—l.*'2” design. (Figure l)
`
`The carbonate system used the same principles for activation
`and initiation, however, to effectively stimulate the horizontal
`carbonate section, multiple ports at spaced intervals would be
`required. Through numerous design iterations, a proprietary
`jetting sub was designed built that would allow various size
`nozzles to be placed within a single jetting sub and also allow
`multiple subs to be placed between the open hole packers.
`The engineering challenge was then to isolate all the nozzles
`for pressure integrity until the stimulation for each specific
`section was to be pumped. This challenge was accomplished
`by plugging the nozzles and establishing communication by
`using a ball and sub to active the nozzles. In conjunction with
`this system design was the development of a computer
`analysis program to optimize the nozzle configuration within a
`specilicd horizontal length for best stimulation and production
`results.
`
`Case Histories
`
`Over the last three years there have been more than two
`hundred open hole systems installed with more than 800
`stages pumped in producing formations of sandstone, shale,
`limestone, dolomite and coal. To date the maximum number
`of stages pumped at one time has been nine. The maximum
`continuous pump time has been 26 hours and the maximum
`pumping rate has been 130 BPM. In one horizontal well, with
`eight stages, 3.5 million pounds of proppant was pumped.
`These systems have been routinely deployed in horizontal
`wells of+4,000 It in length, with the maximum horizontal well
`run in to date being 6,700 ft.
`
`Through this experience, there have been certain aspects of the
`system that vary compared to conventional operations in
`comparable areas or formations. The fracture initiation
`pressure is nearly always less than compared to cemented and
`perforated applications, but higher than compared to open l1ole
`bullheading applications. Evaluating this aspect of the system
`makes logical sense. When cementing and perforating, the
`fracture initiation pressure will in most likelihood be higher
`due to the cement and skin damage created by the operation.
`When bullheading in open hole, the fracture initiation pressure
`will be where the rock strength is weakest along the entire
`horizontal wellbore. Using the open hole packers to segment
`the horizontal wellbore, the fracture initiation pressure will be
`
`where the rock is weakest in that particular segment of the
`well and there will only be one segment where that pressure is
`as low as the bullheading scenario. The pressure variation of
`the system within each segment of the well has proven
`invaluable when determining the effectiveness of the
`mechanical diversion. What has been witnessed in the field is
`
`when the horizontal wellbore is partitioned, each compartment
`has a unique pressure signature for fracturing and or
`stimulating. (Figure 2) This unique pressure signature for
`each stage provides real time evidence that the packers are
`providing the mechanical diversion for which they are
`designed. If the fracture or stimulation was going past the
`packer, then the pressures would be the same for the adjacent
`interval.
`
`The extensive field experience of these systems has also
`provided great insight into the efficiencies, cost savings and
`enhanced production of utilizing the continuous multi-stage
`open hole fracturing/stimulating system. In nearly every case,
`all the fractures and.-‘or stimulations have been pumped in a
`single operation, taking less than a day to complete. In direct
`comparison to horizontal wells that previously had been
`completed by cementing in the liner and using composite
`plugs for mechanical diversion, the cost and time savings have
`been astounding. Comparing four wells drilled offset to one
`another with the same horizontal length yielded the following
`results. The average well completed by cementing,
`perforating and setting plugs took 14 days to complete five
`stages. The two wells using the open hole fracturing system
`averaged 13 hours to pump six stages. This resulted in more
`than 13 days saved in completing the well. Although the time
`and cost savings were significant, the true reward was the
`greater than five fold average production increase that was
`realized by using the system. This trend is indicative of other
`results that have been realized where the system has been
`utilized.
`
`Conclusions
`
`Although horizontal drilling has grown rapidly over the last
`decade there are still areas where improvements can have vast
`impacts on successful reservoir production and depletion.
`In
`200] a technology gap was identified for horizontal wells with
`open hole completions, where mechanical diversion was
`needed to effectively fracture andfor stimulate sections of the
`lateral that were not being treated effectively or in some
`instances treated at all. It is from these initial system
`developments that the horizontal open hole
`fracturinglstimulation system that exists today was spawned.
`A mechanical open hole packer was developed specifically to
`withstand the harsh environments encountered in the high
`pressure fracturing market. The packer was designed to hold
`10,000 psi differential pressure at temperatures up to 400”F
`and have expansion capabilities of more than 40% the original
`packer OD. System developments also included tluid
`deployment systems to be placed between the open hole
`packers to deliver the desired stimulation fluids. Two systems
`were designed, the fracturing por1, primarily for pumping
`proppant and fracturing and the jetting sub, primarily for
`ptunping acid into carbonate formations.
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`Exhibit 2003
`IPR2016-01517
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`Nomenclature
`ft.
`ID
`
`MD
`OD
`
`ppf
`psi
`TD
`TVD
`
`= feet
`= internal diameter
`
`= Measured Depth
`= outside diameter
`
`= pounds per foot
`= pounds per square inch
`= Total Depth
`= True Vertical Depth
`
`This field proven system is now over three years old, with
`more than 200 successful systems deployed in horizontal
`wellbores. The versatility ofthe system is evident in the
`application span which the system has been run. These
`applications include wells from 1,000 it TVD to 15,000 ft
`TVD, in horizontal wcllborcs ranging in length from 500 It to
`6,700 It and in fonnations from coal to shale to sandstone and
`various carbonates. Further evidence of the versatility in
`design of the system is the ability to design the stages at the
`rig site and p111 components from the two systems together.
`some carbonate environments today, the optimum system
`being run is a combination of the fracturing ports with the
`jetting subs, all which are separated by the high performance
`open hole packers which give the mechanical diversion for the
`purnped fluid.
`
`In
`
`It has been through these several hundred case histories that
`the many eflieieneies and benefits have been witnessed. Many
`horizontal wells that previously were completed using the
`cemented mechanical diversion system of setting composite
`plugs and perforating have reverted to the open hole system
`with mechanical diversion due to the operational efficiencies it
`affords. By pumping all the designed fractures or stimulations
`required in the horizontal wellbore in a single day, the well
`can be placed on production, weeks if not months ahead of
`previous systems being utilized. With pumping equipment in
`high demand, a single mobili7ation and pumping operation
`becomes very beneficial.
`
`Acknowledgements
`The authors would like to extend a special thanks to the
`operating companies who provided us the opportunity to run
`and test our equipment in the field. Without their valuable
`input and support these developments would not have been
`possible.
`
`References
`
`l. Garfield, (3., “Formation Damage Control Utilizing
`Composite—Bridge—Plug Technology for Monobore,
`Multizone Stimulation Operations,” SPE Paper 70004,
`presented at the Pennian Basin ()il and Gas Recovery
`Conference, 15-17 May, Midland, Texas.
`2. Rodgerson, J.].., Ruegamer, M.I.., Snider, P., “External
`Casing Perforating Provides Optimal Treatment Coverage
`in Horizontal Pay," SPE Paper 97 l?'5, presented at the
`2005 SPE ATCE, Dallas, Texas, October 9-12, 2005.
`3. Moharnmed, S.I(., Nasr-El-Din, H.A., Erbil, M.M.,
`“Successful Application of Foamed Visco-elastic
`Surfactant—Based Acid," SP].-I Paper 95006, presented at
`SP].-' European Formation Damage Conference, 25-27
`May, 2005, Sheveningen, The Netherlands.
`lirantz, J.II., Williamson, .l.R., Sawyer, W.K., Johnston,
`D., Waters, (3., Moore, L.P., MacDonald, R..l., Pearcy,
`M., Ganpule, S.V., March, K.S., “Evaluating Bamett
`Shale Production Performance Using an Integrated
`Approach,” SPE Paper 9691?, presented at the 2005 SP}.-I
`ATCE, Dallas, Texas, October 9-12, 2005.
`
`4.
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`4 of 5
`40f5
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`Exhibit 2003
`Exhibit 2003
`IPR2016-01517
`IPR2016-01517
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`

`
`
`
`Figure I — 8 Stage
`
`Hole Mechanical Diversion System
`
`
`
`Figure 2 — Chart showing pressure signature for difierem
`stages pllmpedinhmizontal well
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`5 of 5
`5 of 5
`
`Exhibit 2003
`Exhibit 2003
`IPR2016-01517
`IPR2016-01517