SPE 125084

Composites Improve Well Construction Efficiency Jamie Imhoff, Don Parmer, Ben Ronck, Kenny Smith, and Yusheng Yuan, Baker Hughes Incorporated

Copyright 2009, Society of Petroleum Engineers This paper was prepared for presentation at the 2009 SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, USA, 4–7 October 2009. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract After cementing a new liner section during wellbore construction, the liner wiper plugs and landing collar must be drilled out to proceed with the next well section. Current conventional aluminum systems produce considerable resistance and wear to drilling equipment resulting in increased effort and time to drill out the components. The conventional aluminum tools are typically drilled out in 4 to 16 hours. This paper discusses the development, laboratory testing, and field testing of composite liner wiper plug systems for two-plug and four-plug applications that dramatically reduce standard drill-out times, ease the development path for future plug designs, and open doors for other drillable products. The composite liner wiper plug systems include running tools, liner wiper plugs, pump-down plugs, and landing collars that perform multiple functions during the liner cementing process. In addition to the cost savings associated with reduced drill-out times, the systems provide wellbore fluid isolation for cementing integrity, reliable fluid displacement, high-pressure and high-temperature performance, positive bump indication, clear flow paths for setting ball compatibility, and special contingency backups. The composite material needed excellent drillable properties without compromising performance and reliability. The lab results matched the ratings of conventional plugs and landing collars. The systems have completed many successful runs and are gaining favorable reception from our customers and operations personnel. With drill-out times of less than one hour, these initial results represent a significant reduction in rig time and operational costs, adding savings and value to the completion solution. Introduction A liner wiper plug system includes a pump-down plug, a liner wiper plug, and a landing collar. The pump-down plug is dropped from the surface to separate cement from other wellbore fluids and to wipe the drillpipe string. The liner wiper plug is released downhole from a retrievable running tool and serves the same purpose for the liner string. Both are meant to ensure a clean liner cement job. The liner wiper plug lands in the landing collar, creating a seal, just above the shoe track. A “bump” pressure read at the surface indicates that the plug has landed. The landing collar may also incorporate a ball seat that may activate other hydraulic equipment with pressure. A liner wiper plug system may be two-plug, consisting of one pump-down plug and one liner wiper plug (Fig. 1), or four-plug (Fig. 2), consisting of two pump-down plugs and two liner wiper plugs. In the four-plug system, the first plug, or lead plug, is dropped ahead of the cement and the second, the follow plug, is dropped behind the cement. A typical process for a two-plug system is to: 1. drop ball onto landing collar ball seat to set liner hanger 2. shear out ball seat to provide cement path 3. pump cement into drillpipe 4. release pump-down plug from surface to wipe drillpipe 5. land pump-down plug at the bottom of the drillpipe string; liner wiper plug releases to wipe liner 6. land the liner wiper plug wipes in the landing collar; a bump pressure indicates proper cement displacement 7. drill out plugs and landing collar along with the shoe track before continuing on to next hole section

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Conventional landing collars have been constructed of drillable materials such as aluminum. While functional, these materials have presented problems and limitations. The primary concern for operators has been the lengthy drill-out time. Drilling through a metal such as aluminum can result in a slow penetration rate, costing the operator hours of rig time. A typical landing collar can have a thick-wall cross section ranging from .9 in. for a 4.5-in. landing collar up to almost 6 in. for a 16-in. landing collar. Another .5 in. to 1 in. of thickness can be added if a ball seat is used. The result of the thick cross-section landing collar in conjunction with the aluminum liner wiper plug and pump-down plug is a large volume of aluminum that must be drilled out before continuing on to the next section of hole. The aluminum itself presents a problem. Aluminum debris from the plugs and landing collar can clog the drill bit, which may require pulling the drillstring out of the hole to clean the bit before continuing. At high temperatures, the aluminum will become malleable, further complicating the drill-out process. PDC bits are generally not recommended for drilling through aluminum, so an operator may have to use one style drill bit such as a mill tooth bit to get through the landing collar and shoe track then change to a PDC bit to continue (Devereux 1998). For a solution, oilfield service companies have sought materials that can be easily drilled out with any style bit and still function with at least the same ratings as the aluminum equipment. Advanced high-performance composite materials were chosen due to their high strength, environment-resistant capability, and drillability. While widely used in the automotive and aerospace industries, the oilfield downhole environment presented challenges in material selection. Specifically, the properties of many composite materials begin to degrade when exposed in well fluids under elevated temperatures, referred to as a hot-wet condition. Material selection required testing to simulate the downhole environment. Material properties were then derived based on this testing. The geometry of each part also dictates material properties due to the manufacturing process required to achieve the geometry. It was discovered that the process of the composite materials was the key to achieving the required mechanical strength. Overview Composites are a broad class of materials with a very wide range of possible physical, mechanical and chemical properties. However, some generalizations can be made about them to aid in the basic understanding of their utility in designing oilfield products. Composite materials have several advantages over conventional metal materials for certain downhole applications. Composites are easily drilled up compared to aluminum and cast iron. Composites are compatible with all bit types, freeing the operator to make decisions based on the well environment. In addition to drillability, composites are lightweight compared to aluminum and are generally corrosion-resistant. Many composites are also erosion-resistant and are therefore good candidates for applications that could encounter wash-out problems. Composites do have some limitations to their use in the oil field. They are generally not as strong as metals per unit volume. This can limit their use when loads are high or cross sections are limited. They are generally more temperature-sensitive than metals, and can be brittle and prone to cracking. Some composites are not suitable for extended service in hot-wet environments. Some of the composites used in the oil field perform better in compression loading than tensile loading. Generally, as mechanical and other material property requirements rise, so does the cost of completed composite parts. This is due to increased materials cost and more expensive processing methods that may be required to meet more stringent design requirements. Design Designing composite components is a very different process from designing metal components. The designer must understand their anisotropic properties, constitutive laws, and analysis technologies. Also required is knowledge of the different physical properties of composites along with the many different manufacturing processes such as mandrel wrapping, injection molding, compression molding, and filament winding. The goal for molded parts is to have 100% final geometry out of the mold. Generally, this is not practical, but many molded components get very close, only requiring a few minutes of cleanup with a knife or grinder to remove mold sprues or flashing. Material Selection: The hot and wet downhole environment presents a particular problem for polymers and polymer composites. Many are susceptible to hydrolitic and hydro-thermal degradation. This can alter their performance significantly when compared to their original dry state. (Yuan, Goodson 2007a)

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Water causes damage to composites in several ways. The first is mechanical damage caused by uneven swelling. As the polymer matrix material absorbs water it will swell, generating residual stresses within the composite material. These stresses can lead to internal micro cracking or delamination. They can also damage the bond between the matrix and the fibers. These problems can be exacerbated by the fact that, in thick–section composite components where the moisture absorption and swelling will not be even, a residual stress gradient may result. (Yuan, Goodson 2005) Water can act as a plasticizer to the matrix material and lower its glass transition temperature, leading to mechanical degradation at elevated temperatures. Water can also attack the matrix by breaking the chemical bonds of the polymer. Salt and other common wellbore contaminants can exacerbate these problems. Water can also leach substances out of the matrix, such as the byproducts of the water’s attack on the matrix material. (Yuan, Goodson 2005) All of these potential problems mean the composite material must be carefully tailored to match the wellbore environment. Glass fibers have been shown to be susceptible to damage in hot-wet conditions. (Yuan, Goodson 2007b) Glass fibers still see wide uses in oil fields for lower-temperature or short-term applications for several reasons. They are a significantly less expensive than carbon fibers. Proper resin selection, such as using phenolics, protects the fibers from damage by resisting water and chemical absorption. With consideration of the downhole environment-resistant capability of various composite materials and the operational requirements of the two-plug and four-plug liner wiper plug systems, the following composite systems were selected for these applications.

Short Fiber-Reinforced Molded Composites: Chopped glass fiber-reinforced phenolic composite molding compound was chosen for the two-plug liner wiper plug system for a number of reasons: (1) This wiper plug system is rated at 300°F and 5000 psi for a short-term downhole duration (24 hours) and no significant axial and collapse loading is applied on the plug bodies during the operation; (2) Phenolic resins have been proven to resist the hot-wet environment to a temperature at 300°F or even higher in the wellbore; (3) Although glass fibers have the hot-wet degradation issue in downhole environment, but the application is in a short term. In the four-plug liner wiper plug system, the flapper in the follow liner wiper plug is a critical part to run the system since it will be loaded directly under 5000 psi pressure differential at 300°F with small supporting area and complicated geometry (Fig. 3,4). With consideration of the geometry of the flapper, a molding process is preferred. To ensure a successful prototyping, multiple advanced composite molding compounds were considered, including carbon-fiber/PEKK, carbon-fiber/PEEK and an advanced carbon fiber reinforced high-temperature, hot-wet resistant thermosetting matrix composite. PEKK and PEEK are known as advanced thermoplastic engineering resins providing excellent hot-wet resistant capability. However, the prototype parts molded from the PEKK and PEEK composites failed or barely passed the test at 300°F and 5000 psi in water without a solid safety factor because of the limitation in glass-transition temperature of these two resins (below 300°F). Successful prototyping was achieved for the molded follow flapper by using the high-temperature, hot-wet resistant thermosetting molding compound. The material’s mechanical performance at the application temperatures was not an issue since its glass transition temperature in wet environment is well above 300°F. The prototype parts not only passed testing, but far exceeded the load requirements during failure tests to provide large safety factors. (Fig. 5) For molded composites with random short fibers, chopped fiber lengths can be varied to different lengths such as ¼ in., ½ in., 1 in.or 2 in.. Shorter fibers are easier to mold with more consistent results due to their ability to flow more easily into the various mold geometries. However, longer fibers provide higher strength in general, due to the increased interlacing of the longer fibers.

Continuous Fiber-Reinforced Laminated Composites: Continuous fiber-reinforced composites differ from short fiber-reinforced molded composites in several aspects. In general, the continuous fiber-reinforced composites are manufactured by more expensive processing methods such as filament winding, tape placement, and hand wrapping, with relatively higher cost. The continuous fiber-reinforced composite components can offer increased mechanical stiffness and strength for more critical applications; however the design process is more involved, as the fiber orientations need to be carefully chosen based upon the anticipated loading condition. A continuous fiber composite is commonly a laminated composite structure. During the manufacturing operation, the fiber angle can be varied from layer to layer to orient the fibers and augment the material strength with respect to the desired combined tensile, compressive, and hoop properties. This increased both process time and cost

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significantly over molded components. These methods can be used to produce parts much larger than any molding process could. In the four-plug liner wiper plug system, the plug noses and bodies are highly loaded components in cylindrical shape. Continuous glass fiber-reinforced high-temperature epoxy composites are preferred for these critical components for 300°F short-term applications. Filament winding and fabric wrapping processes were used to manufacture these cylindrical components in different sizes, respectively. The filament winding process can build thick section components in large-sized tools more effectively. To finish the parts, certain machining work to the wound or wrapped composite components is needed. Manufacturing Process and Design Iterations: When work first began on the two-plug system, an unsuccessful attempt was made to use compression molding. The composite material that was chosen is usually compression molded. The part geometry was much more suited for transfer molding. The compression molding did not work with the part geometry and we were unable to get good parts out of the mold. After modifying the mold for transfer molding techniques, we were able to produce good parts. This balancing of two different criteria, the material and the manufacturing technique, is a good example of the particular challenges involved with using composite materials. The transfer molding process involves using a hydraulic piston to force the pre-heated, uncured composite material into the mold through a series of channels called sprue holes. The pressure on the material, along with the heated mold, begins to cure the material. Once the process variables such as pre-heat temperature and time, injection pressure, and mold temperature are fine tuned, parts can be produced with good dimensional accuracy and repeatability. As parts get larger, it becomes more difficult to hold the tight tolerances that designers are used to specifying in designing with metals. This is because components are molded at high temperatures; therefore parts will shrink as they cool. For simple geometries such as tubulars, these effects are relatively easy to predict. As geometries become more complex, the volumetric shrinkage and its effect upon the part’s final dimensions become more difficult to predict. The mold designer will do their best to predict shrinkage effects and size the mold such that the final cured and cooled part will match the specified part dimensions within tolerance. Often, though, after a mold is made, parts must be molded and measured, and then the mold can be modified to bring dimensions of the final part into tolerance. A key to successfully designing with molded composites is learning to minimize tolerance stackups. The fewer dimensions that require tight tolerances, the easier and less expensive a mold will be to develop. Seal surfaces of mating composite parts are a particular area where this can become an obstacle to a successful design. One solution is to mold seals directly onto composite components as a bonded seal. Another solution to the tolerance stacking issue is to design mating components such that one is a machined component while the other is molded. This allows easy adjustment of the machined component to match the molded one. The four-plug system was designed primarily with continuous fiber composites, both sheet wrapped and filament wound, at various points in the development process. Filament winding allows parts to be made with very thick wall sections that may be difficult to produce with other methods. The four-plug components were made in several different segments, with each section’s material selection and fiber orientation designed to fit the loading that would be seen by that component, while minimizing the production cost of the total system. Several challenges required modification of the original design. A flapper on the follow plug and its support shoulder see some of the highest loads in the system. This area sees some severe tri-axial loading due to factors such as the bending moment on the flapper and the column and hoop loading on the flapper support shoulder. Thick-section composites in general have poor performance in a tri-axial stress state. This is because even in a molded component that uses short chopped fibers, it is not possible to make truly isotropic components. This is even more true in any filament-wound or sheet-wrapped component because of its laminated structure. To meet this challenge, the flapper was made out of a special high-temperature, high-performance composite molding compound. This would have been too expensive to use in the rest of the tool, but was a good solution for the flapper. Design Analysis: Finite element analysis (FEA) was used to gain a better understanding of the loading and the resulting stress map. The design was then refined with geometry and material selection. This helped to minimize

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testing iterations. For the initial design of the liner wiper plugs with flappers for the four-plug system, a bearing strength of 30,000 - 35,000 psi was assumed based on general material specifications provided by the supplier. In order to provide a substantial safety factor in the designs, nominal bearing stresses of 15,000 – 20,000 psi were targeted using classical analysis. In the four-plug system, the highest-bearing stress occurred between the angled load shoulders of the flapper and the follow LWP nose when pressured to 5,000 psi. FEA of the initial detailed design revealed a stress concentration located at the inner diameter of the load shoulder. (Fig. 6) With the applied pressure load, the original 45° load shoulder angle between the flapper and follow LWP nose produced a stress of over 57,000 psi. In order to distribute the load more evenly across the bearing face, the design was revised to reduce the load angle to 30°. Further FEA revealed that the stress concentration had been reduced in both penetration depth and magnitude to 43,000 psi. (Fig. 7) Since the application stresses at the loading shoulder still exceeded the intended target range, an attempt was made to incorporate a glass fiber fabric prepreg laminated load insert into the follow LWP nose to sustain and distribute the high bearing loads. To sustain the flapper load, the insert’s fibers were oriented to be in compression instead of shear as with the nose’s wound fibers. Because of the high tri-axial bearing stress state, the prepreg lamiated load insert still could not survive. To solve the problem ultimately, a small brass load insert was incorporated into the follow LWP nose to sustain the combined bearing and hoop loads at the highest stressed area of the entire plug system. This brass insert only needed to be large enough to withstand the previously mentioned stresses and have enough surface area to transmit the resulting force vector to the rest of the plug body without crushing it. This insert, along with the flapper springs and the lead plug rupture disk, kept the volume of metal to a minimum, thus substantially easing the drill-out relative to the conventional systems. Designing with composites poses a challenge in that the actual material properties of the final product becomes an additional variable in the development. Unlike metals that provide rather consistent properties, the material strength of composites can be a product of constituent materials, processing method, fiber orientation, part geometry, and exposure to moisture and temperature. Classical engineering stress analysis and FEA require complete and accurate composite material property data that are difficult to obtain in many cases, especially for thick-section composite structures and in a reversed environment. So, true mechanical strength and performance of a composite component can only be determined through prototype testing in many cases. In the case of development of these plugs and landing collars, FEA helped to illuminate stress concentrations and revealed the material strength required for a successful design. In addition to material selection, the proper manufacturing process and geometry were key elements to achieving this strength. Calculations and FEA were initially based on information from the material suppliers, but this data was derived from testing on small coupons. The design team was tasked to develop a portfolio of plug and landing collar sizes. Multiple testing iterations were required for the first sizes, the 7.625-in. two-plug and 9.625-in. four-plug systems. With the successful completion of these designs, engineers gained a better understanding of actual material properties. Though the sizes that followed differed in volume, outer diameters, and inner diameters, the overall geometry and processing methods were similar. So, derived material strength from previous testing made the results more predictable. Thus, there were fewer testing iterations to complete the portfolio. Drill Out: Polymer composite materials are much easier to drill up than the aluminum or cast iron that has traditionally been used for cementing plugs and landing collars. The drill-up properties of a composite will be dominated by its matrix phase. The matrix materials of composites are generally softer than aluminum and have low scratch resistance. Their softness, combined with their relative brittleness, makes them very easy to drill. They do not have a tendency to clog or “gum up” a bit like aluminum. The cuttings are low density and therefore do not require special heavy-weight mud to be recirculated out of the hole. (Garfield 2001) Final Designs and Lab Test Results: The plug systems met all of the current aluminum plug/landing collar ratings in lab testing. Successful testing included plug launch, plug bump pressures at temperature, and ball seat shear-out at temperature. All tests were done at 300°F. It was discovered that the systems perform at even higher pressures at lower temperatures, keeping the doors open for future higher pressure applications.

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The final designs have multiple configurations for greater functionality. For example, the two-plug system incorporates a drillpipe part, liner wiper plug, and landing collar. The landing collar can come with or without a ball seat and ball seat catcher and has the option of a baffle plate. These components are primarily constructed of composite materials. In the plugs, there is a minimum of aluminum to allow the dart to latch into the liner wiper plug. There is also a small aluminum shear ring to achieve a more reliable shear with brass shear screws. The operation of the two-plug system is identical to current aluminum plugs, easing training and acceptance of the new equipment. The four-plug system isolates the cement from other wellbore fluids, providing improved cement quality. This is something operators want, but may be hesitant to use many of the aluminum systems due to lengthy drill-out times. The design presented here alleviates this concern by its use of composite materials. The volume of material has also been decreased because the pump-down plug is retrieved to the surface with the plug launching tool. Although this tool is more costly than the two-plug system, operators save much in drill-out time while being confident in a reliable cement job. The ultimate goal of providing reliable plug systems with the least amount of metal components in the industry was achieved. Field History: Drilling out a plug system for the next well section can involve drilling through the liner wiper plugs, pump-down plugs, and landing collar. Below the landing collar, the liner will be full of cement down through the float equipment and the shoe. The drill-out times required for conventional aluminum systems typically range from 4 to 16 hours. Assuming a typical offshore rig operating rate of $25,000 per hour, the cost of the drill-out operation would fall between $100,000 and $400,000. The prototype composite two-plug system was introduced to the market in 2007. Drill-out times have been reported to vary between 10 and 65 minutes. The newer four-plug system has completed two field runs thus far with drill-out times of less than 1 hour. At the same rig operating rate, the expected cost for the drill-out operation would be $25,000 or less. The drilling efficiency through the composite materials provides a substantial savings in both cost and time, relative to the conventional systems. The plug systems have also proved to be reliable. In one 9.625-in. two-plug system example, the actual cement displacement values matched the calculated values and the liner wiper plug bumped with 1650 psi indication pressure. The drill-out time was 45 minutes with a PDC bit with very limited set-down weight on bit (2000-4000 lb. WOB). Thus far, engineering has received no information on unsuccessful composite plug system jobs or long drill-out times. Conclusion The composite plug system projects discussed here required an upfront investment in research time, mold and manufacturing costs, and testing. The pay-off is a successful product that will benefit operators by streamlining their cementing and drilling operations. From a design standpoint, the larger pay-off is knowledge about the properties of modern composite materials and manufacturing methodologies. Future composite projects will springboard off of the knowledge and data gained from this work. The next step will be to search for high-grade composite materials for higher-temperature applications. Although the downhole oilfield industry is not one of the composite suppliers’ largest customers, it is becoming a unique niche. Suppliers are learning about oilfield applications just as oilfield engineers and material scientists are becoming more savvy about design with composite materials. Future challenges will require a strong collaborative effort. Definition of Terms Composite- Any combination of two or more materials designed such that the materials working together have material properties more suited to the design requirements than either material would separately. The term composite as used in mechanical design usually refers to a strong, stiff but brittle fiber in a relatively tough, resilient polymeric matrix. Examples include common fiberglass, glass-filled phenolics and carbon-fiber-reinforced epoxy composites. Pump-Down Plug- Also referred to as drillpipe dart, a plug dropped from the surface that is designed to separate well fluids from cement and wipe out the ID of a drillstring to ensure cement displacement and minimize cross contamination.

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Liner Wiper Plug- A plug, usually run into the hole on the bottom of a workstring, that is designed to separate well fluids from cement and wipe out the ID of Liner or Casing and to ensure cement displacement and minimize cross contamination. References Devereux, S. 1998. Practical well planning and drilling manual. Tulsa, Oklahoma: PennWell Books. Garfield G. “Formation Damage Control Utilizing Composite-Bridge-Plug Technology for Monobore, Multizone Stimulation Operations,” Paper SPE 70004 presented at the SPE Permian Basin Oil and Gas Recovery Conference in Midland, TX, 2001. Yuan, Y. and Goodson, J. 2007 Hot-Wet Downhole Conditions Affect Composite Selection, Oil &Gas Journal, Sept 10 (a). Yuan, Y. and Goodson, J. HT/HP Hot-Wet Thermomechanical Properties and HT/HP In-Situ Mechanical Test Method of High-Temperature Polymer Composites, Proc. 52nd International SAMPE Symposium and Exhibition, Baltimore, MD June 3-7, 2007 (b). Yuan, Y. and Goodson, J. HT/HP Hot-Wet Thermomechanical Behavior of Fiber-Reinforced High-Temperature Polymer Composites, Proc. Fourth International Conference on Composite Materials for Offshore Operations, Houston, Oct. 4-6, 2005.

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Figure 1: Composite Pump-down plug, liner wiper plug and landing collar for liner cementing. Pump-down plug latches into the liner wiper

plug to seal off the inside of the plug.

Figure 2: Lead and follow liner wiper plugs of the four-plug system sitting on part of its landing collar.

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Figure 3: Liner wiper plug from the four-plug system shows how a flapper is used to close off the inside of the plug.

Figure 4: Liner wiper plug from the four-plug system.

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Figure 5: A view of a flapper in the four-plug system.

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Figure 6: FEA analysis of the flapper load shoulder with the initial 45° contact angle under a 5,000 psi load. Analysis performed using Von Mises Stress.

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Figure 7: FEA analysis of flapper load shoulder with revised 30° contact angle. Analysis performed using Von Mises Stress.