SPE-180818-MS

Proppant Management: A New Challenge to Develop UnconventionalReservoirs in Argentina

J. C. Bonapace, Halliburton

Copyright 2016, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE Trinidad and Tobago Section Energy Resources Conference held in Port of Spain, Trinidad and Tobago, 13–15June 2016.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contentsof 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 reflectany position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the writtenconsent 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 maynot be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

Hydraulic fracturing has become a critical component in the successful development of unconventionalreservoirs; it is well known that constructing an economic well in this type of formation is verychallenging. In the last 15 years, exploration and development of unconventional reservoirs (tight gas) hasbeen initiated. Over the past 5 years, the main target in Argentina has been located in the Vaca Muertashale, which is one of the main source rocks in Argentina. Such a development challenge requires one todevelop a fast learning curve to more quickly achieve economic wells. This type of completion andstimulation involves vast amounts of water, proppant, chemicals, and special equipment, coupled withcontinuous improvements in operations, quality, cost, time, and safety. Various alternatives in proppantmanagement were explored and introduced. This paper describes several aspects related to stimulation ofdifferent tight formations and shales in Argentina, including proppant selection, supply chain, logistics,new storage systems, and laboratory studies performed on local white sand. The focus will be on these keyaspects:

● Stimulation: information about proppant type, amount, and size for hydraulic fracturing performedin several tight and shale formations in Argentina with more details of the Vaca Muerta formation.

● Logistics and supply chain: improvements introduced from transportation, storage, and handlingof proppant, including the evolution process over the last few years, from centralized storage sitesto the wellsite.

● Laboratory: several samples of white sand procured from different parts of Argentina wereevaluated to be used in hydraulic fracturing. API and ISO standards were used for qualifying testsincluding specific gravity (SG), bulk density, acid solubility, turbidity, sphericity, roundness, sieveanalysis, and crush strength.

IntroductionHydraulic fracturing is one of the most-widely used stimulation techniques in Argentina. The firstapplication dates back to 1960 in the Sierras Blancas formation and was completed with 200,000 lbm ofproppant (white sand). Since then, this type of treatment has been performed in five producing basins in

the country (Fig. 1a) and in a variety of formations and types of reservoirs, such as conventional, tight,and more recently in shale (source rocks).

Over the last 55 years, different types of proppant have been used: natural sand, resin coated proppant(RCP), man-made proppant usually called ceramics (classified as low, medium, and high density or low,intermediate, and high strength proppant) and several meshes, such as 8/12, 12/20, 16/30, 20/40, 30/50,40/70, and 70/140 (nominally 100 mesh), according to the reservoir requirement.

Historically, the origin of these proppants was mainly from USA (white sand, RCP, and low andmedium density ceramics) or from Brazil (medium to high density ceramics/bauxites). Because of theproximity to Brazil, the low cost of transportation has generated a particular situation in which this typeof proppant was used in several cases despite the proppant exceeding the formation requirement for stressresistance. The Brazilian ceramics were less costly than those imported from the USA and so econom-ically more convenient for the projects [d’Huteau et al. (2007) and Antoci et al. (2001)].

In the 1980s, searches and studies of natural local sand deposits were conducted to evaluate thefeasibility of use in hydraulic fracturing applications without success. These studies were performed forservice companies and operators with the intention of achieving an alternative local proppant to optimizethe cost of the projects and reduce the effect of global price fluctuations.

Initially, the first treatments in unconventional reservoirs (2001) were in tight formations in whichseveral operators began exploration. The development phase was primarily in the Neuquén Basin (Fig.1b), focusing on the Lajas, Punta Rosada, and Mulichinco formations. Some treatments were performedin the Potrerillo formation (Cuyo Basin) and, in the last five years, two operators have begun to evaluatethe D-129 formation in Golfo San Jorge basin (GSJB). Early work using hydraulic fracturing to developArgentina’s shale basins was conducted during 2010. The majority of exploration and development hasbeen in the Vaca Muerta (VM) formation, but applications have also been assessed in other formations,

Figure 1—(a) Map of five Argentina hydrocarbon producing basins; (b) Neuquén Basin geographical subdivision.

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such as Los Molles, Cacheuta, D-129, and Agrio more recently. The exploration and development of theseunconventional projects showed a steady increase in use and consumption of particular proppants (initiallymedium density ceramic or intermediate strength proppant) and various mesh ranges (50/150, 70/140,40/70, and 30/50).

As part of any field development, the optimization costs have an important impact in the life of theproject. Achieving a cost effective completion is very important, and one of the main drivers is optimizingthe hydraulic fractures by using the right proppant. Schnaidler et al. (2013) documents this aspect for atight reservoir in the Neuquén basin. More recently in the VM formation several operators have startedto use white sand proppant. This practice in the US is well documented in French et al. (2013) andProchnow et al. (2014). Some publications presented examples of reservoirs in which non-API proppantwas used, showing similar productions to wells stimulated with standard proppant (Cramer 2008; Juraneket al. 2010; and Adeyeye et al. 2013).

Reservoir Conditions for Proppant SelectionIt is well known that the strength of the proppant grains is of major concern in the design of proppedfractures. Traditionally, in-situ closure stress on proppant in the fracture is estimated as minimumhorizontal in-situ stress minus bottomhole flowing pressure (FBHP). Based on this calculation of thein-situ stress closure stress on the proppant, engineers are able to select suitable strength proppants for thefracturing treatment. It is generally accepted that in the lower closure stress environment (below 6,000 psi,shallow reservoirs), white sand is commonly used, and at higher stress levels and deeper reservoirs,manmade proppants are used. A summary of the main values for proppant design of tight and shalereservoirs in Argentina is presented in Table 1. This information was collected from more than 200diagnostic fracture injections tests (DFIT) performed in these formations.

A more detailed study was performed for Mulichinco, Punta Rosada, Lajas, and Vaca Muertaformations. Fig. 2 presents the values of minimum horizontal stress (Fig. 2a) and reservoir pressure (Fig.2b) identified from 150 DFITs for all formations. Higher values of minimum horizontal stress areobserved for Lajas Punta Rosada and Vaca Muerta formations, as well higher reservoir pressures for Lajasand Vaca Muerta. To estimate the closure stress on proppant, a bottomhole flowing pressure of 70% ofthe reservoir pressure obtained from the DFIT was considered; this value is very close to the FBHP thatwas reported for several operators consulted. Finally, in Fig. 2c the closure stress on proppant is presented;the value is between 1,000 to 5,000 psi for this location.

Table 1—Summary of Argentinian reservoir conditions.

Basin Reservoir Formation Depth (ft) BH Temp. (°F) Min-Hzt Stress (psi) Res. Pressure (psi)

Neuquén Shale Agrio 10,950 224 10,868 8,020

Neuquén Shale Vaca Muerta 7,550 – 10,950 175 – 225 6,300 – 10,400 5,600 – 9,600

Neuquén Shale Los Molles 11,100 224 9,871 7,741

Neuquén Tight Mulichinco 4,950 – 6,400 134 – 156 2,350 – 4,900 1,300 – 3,290

Neuquén Tight Punta Rosada 9,500 – 1,2650 205 – 250 4,400 – 10,800 3,630 – 8,000

Neuquén Tight Lajas 12,900 255 10,275 9,491

GSJ Tight D-129 9,700 – 10,000 210 – 230 5,060 – 7,100 3,900 – 4,500

GSJ Shale D-129 11,680 235 8,380 5,267

Cuyo Shale Cacheuta 11,190 256 10,210 8,173

Cuyo Tight Potrerillo 11,870 268 12,188 9,050

SPE-180818-MS 3

Proppant Type and StimulationAll of the hydrocarbon producing basins in Argentina are considered to be unconventional resources. Theprimary location of development of these reservoirs is in the Neuquén Basin. Hence, the focus on thispaper is on this area. A geographical segmentation was performed in three major areas (east-blue,south-green and west-red), defining the Los Barreales dam as the midpoint reference (Fig. 1b). A varietyof fields according to their location in the basin have tight and shale reservoirs in the vertical section ofa well, making possible the development of multi-target well completions.

Types of Treatments in Shale plays

Fig. 3 presents the principal usage characteristics of proppants for various Argentina shale reservoirs. Fig.3a shows the average proppant volumes per stage (lbm) according to the reservoir fluid type; Fig. 3bpresents the average percentage for type of proppant used; and Fig. 3c presents the average percentage foreach mesh size pumped.

Figure 2—(a) Minimum horizontal stress vs. depth; (b) Reservoir pressure vs. depth; (c) Closure Stress on proppant vs. depth forunconventional reservoirs in Neuquén Basin.

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For Agrio, D-129 and VM formations, the average proppant per stage is very consistent (475,000lbm/proppant). Different values are presented for Cacheuta and Los Molles formations (Fig. 3a). Only inCacheuta formation was HSP used; for the other plays, white sand and ISP were combined. In VM, thehighest percentages of sand (54%) were used (Fig. 3b). In most of the formations, four mesh proppant wasused. In Los Molles, two mesh proppant was used. The higher percentages of mesh size used correspondedmainly to 40/70 and 30/60. These two mesh sizes are approximately 65% to 80% of total proppant used(Fig. 3c).

Types of Proppant for Vaca MuertaThe main proppant usage characteristics for the Vaca Muerta formation are presented in Fig. 4, andclassified as vertical or horizontal wells. A classification by subgroup of well is presented according tothe geographic location shown in Fig. 1b: western zone (H1, H2), eastern zone (G1, G2, G3, J1, S1, S2,S3), and southern zone (A3, A4, C1, K1, M1).

Figure 4—(a) Average proppant volume per stage (lb); (b) Percentage according to the type of proppant; (c) Percentage according tothe mesh size (Vaca Muerta formation).

Figure 3—(a) Average proppant volume per stage (lb); (b) Percentage according to the type of proppant; (c) Percentage of mesh sizeused for several Argentina shale plays.

SPE-180818-MS 5

In general, the types of proppants used are white sand or ISP (low or medium density) as shown in Fig.4b. Depending on the mesh size of the proppant, between three to four mesh sizes are used (100, 40/70,30/50, and 20/40). In some cases 20/40 is not used, and in other cases, 100 mesh or 40/70 is not used (Fig.4c). For vertical wells, the average proppant used per stage is close to 500,000 lbm for most wells alongthe basin, depending on the type of reservoir fluid (Fig. 4a). A typical completion for a vertical wellincludes 4 to 5 stages and uses a total of 2.0 to 2.5 million lbm of proppant. For horizontal wells, the valuevaries depending on the subgroup, as presented in Table 2.

Types of Treatments in Tight FormationsFig. 5 presents the principal characteristics of proppant usage for various tight reservoirs in Argentina. Fig.5a shows the average proppant volumes per stage (lbm) according to the reservoir fluid type, Fig. 5bpresents the average percentage for type of proppant used, and Fig. 5c presents the average percentage ofmesh size pumped.

In general, the average amount of proppant per stage for several tight formations in Argentina variesbetween 140,000 to 193,000 lb (Fig. 5a). The main difference is in relation to the type of proppant andmesh size. Potrerillo formation is the only one where HSP was used; the rest of the formations use mainly

Table 2—Summary of horizontal completions in Vaca Muerta formations.

SubGroup Well Hztal Section No. of Stimulations Avg Prop per Stage Total Well Prop Used

A4 1,600 ft 8 Stages 300,000 lbm 2.40 million lbm

G2 5,600 ft 17 Stages 490,000 lbm 8.30 million lbm

H1 & H2 4,600 ft 11 Stages 475,000 lbm 5.22 million lbm

S1 & S2 4,900 ft 20 Stages 370,000 lbm 7.42 million lbm

Figure 5—(a) Average proppant volume per stage (lb); (b) Percentage according the type of proppant; (c) Percentage of mesh sizedused for several Argentina tight formations.

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ISP, with some use of RCP and white sand (Fig. 5b). Depending on the mesh size, the two primarily usedin all the formation were 30/60 (except in Mulichinco formation) and 20/40 (Fig. 5c).

Types of Proppant Used in the Neuquén Basin Tight FormationsThe main proppant characteristic for these formations are presented in Fig. 6. A classification byformation and subgroup of well is presented according to geographic location (Fig. 1b): western zone (D3,H1), eastern zone (G2), and southern zone (D1, D2).

In the Neuquén basin, the types of proppants used for Mulichinco, Punta Rosada, and Lajas formationsare white sand, RCP (sand), and ISP, or combinations of these (Fig. 6b). Depending on the mesh size ofthe proppant, most of the formations use a combination of two mesh sizes: 40/70 � 20/40 or 30/60 �20/40 (Fig. 6c). The average proppant per stage is close to 150,000 lbm. One particular group of wells inMulichinco used a larger amount of proppant (275,000 lbm / stage) as shown in Fig. 6a.

In the Lajas formation, the main differences between the two subgroups of wells are the type ofproppant and percentages of mesh size used; the amounts of proppant used per stage are very similar. Inthe Mulichinco formation, there are more differences between the vertical wells (subgroup D2 and D3)and horizontal wells (subgroup H1). Variations are found in the amount of proppant per stage, the typeof proppant, and the mesh sizes used. A summary of the well completions for each formation are presentedin Table 3.

Figure 6—(a) Average proppant volume per stage (lbm); (b) Percentage according to the type of proppant; (c) Percentage accordingto the mesh size used.

Table 3—Summary of completions in tight formations.

SubGroup Well Type of Well Formations No. of Stimulations Total Well Prop.

D1 Vertical Lajas & Punta Rosada 2 – 10 Stages 1.8 million lbm

G2 Vertical Lajas 9 Stages 1.45 million lbm

D2 Vertical Mulichinco 2 Stages 825,000 lbm

D3 Vertical Mulichinco 3 Stages 555,000 lbm

H1 Horizontal Mulichinco 15 Stages 1.8 million lbm

SPE-180818-MS 7

Patel et al. (2014) and Gallegos and Varela (2014) present a detailed analysis of the evolution andtrends of the types and amounts of proppant used in hydraulic fracturing for various basins in the US,which can be evaluated comparatively with the information presented in this publication for various playsin Argentina.

Logistic and Supply ChainHydraulic fractures are central to the completion of unconventional reservoirs. Proper planning andpreparation for large volumes of proppant are required, and water and logistics (equipment) are necessaryto achieve an efficient completion in terms of time and cost. Several works document proppant logisticsfor cases around the world: Marcellus, US (Perkins 2008), British Columbia, Canada (Tymko et al. 2010),Qiongzhusi, China (Zonggang et al. 2012), and Chicontepec, Mexico (Gutierrez et al. 2014).

Traditional Proppant Supply ChainHistorically, proppant supply in Argentina was developed as follows. The proppant (natural sand, RCP,ceramic) was imported into the country from manufacturing centers primarily in the US, transported bysea (vessel) in a container whose capacity was 33 tons; typically in 22 large bags, each one with a capacityof 1.5 ton (3,300 lbm), entering the country through Buenos Aires port. Supply from Brazil only differsby rail transportation, rather than by sea. In general, most suppliers developed logistics hubs in BuenosAires, or in some cases of oil activity, the city of Neuquen.

Transport from logistics hub of Buenos Aires to oil productive basins was carried out by road in truckswhose maximum capacity was around 27 tons (60,000 lbm). A very good logistic and coordination planwas necessary to bring supply to different parts of the country including Neuquén (Neuquén basin),Comodoro Rivadavia (GSJ basin), Rio Gallegos (Austral basin), and Mendoza (Cuyo basin).

The storage centers in these cities were in warehouses maintained by the proppant supplier, the servicecompany, or the well operator. Then, transport to the wellsite was conducted by road (truck), eitherthrough transport trucks with large bags (27 ton-60,000 lbm) or through special bulk transport units (sanddump trucks).

For smaller jobs, sand dump units at the well site were used (loaded at the storage center usingconveyor belt), but for large operations, wellsite storage equipment (400,000 lbm per storage unit) wasmanually loaded by personnel using cranes or forklifts to handle the large bags. The workflow is shownin Fig. 7.

Figure 7—Traditional and current proppant supply chain.

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As a result of the development of unconventional reservoirs over the last seven years, some variationshave occurred in several parts of this workflow. Examples of these are the following: a greater need forstorage capacity at storage centers, excessive manipulation of the large bags, more traffic from transportsfrom the storage center to wellsite, greater storage capacity requirements at the wellsite, larger locationswith more space, incremental increases in manipulation and resources (equipment, personnel), andreal-time reloading of proppant during operations; each of these potentially contributing to unsafepractices. As mentioned previously, it became necessary to explore alternatives for improving the supplychain logistics for these types of operations, as had been implemented in other unconventional plays inthe US.

A New Model for Proppant Supply ChainThe primary development of unconventional reservoirs to-date has been in the Neuquen basin. This areawas chosen for the proppant supply chain improvements. Fig. 8 presents this workflow with severalchanges and improvements.

This new concept was defined in 2011-12, with some equipment plants built during 2013-14 and useof those facilities in 2014-15. The model was divided into three main parts: the first is related to proppantimport and transport, the second is for loading and central storage (plant), and the third is for bulktransportation and wellsite operation.

● First Part: A new port, Bahia Blanca, was identified to improve two aspects of import andtransport. It was a short distance to the Neuquen basin (reduces road distance), and transport wasimproved using a breakbulk vessel with a capacity of up to 10,000 tons per vessel. A futureimprovement will be using a vessel with bulk proppant transport capabilities for imports into thecountry. To move proppant from port Bahia Blanca to the new plant in Neuquen, a system withmultiple options was developed. In the first stage, flatbed trucks were used (for large bagtransport), and a pilot test using rail was performed.

Figure 8—New model for proppant supply chain.

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● Second Part: This stage included using conveyor belts for loading large bags to bulk transport unitsand a large plant for proppant storage. These changes improved loading speed, offered differentoptions for loading (plant or satellite center), increased the storage capacity, and allowed forhandling several mesh sizes separately.

● Third Part: This stage considered the proppant transport from the plant to the wellsite (bulktransportation) and the bulk loading into the wellsite storage units. The main objectives for thispart of the process were to improve the velocity (time), to develop a more efficient dischargesystem, to improve work safety, and to reduce wellsite space and resources used by the traditionalsystem.

Storage Plant A storage plant was built between 2013 and 2014 and inaugurated in October of the sameyear. The concept of this storage plan was to optimize the storage and loading for the delivery process forthe increasing volumes of activity in unconventional fields in the Neuquen basin. The storage plant islocated in Neuquén city, 6.5 miles from the Neuquén Operational Base.

This facility consists of a warehouse (650 m2 with 1,200 ton/2.6 million lbm of proppant capacity), 3Silos (1,800 ton/3.9 million lbm capacity), and an advanced, efficient, and safe system for loadingproppant onto bulk proppant transportation trucks (sand trucks), using a fast loading gravity mechanism(Fig. 9a, b, and c).

The current storage plant capability, including the warehouse and silos, is approximately 3,000 ton/6.5million lbm. Additional proppant storage of about 18 million lbm is available in 3rd party warehouses in

Figure 9—(a) Storage plant (silos) and warehouse; (b) Proppant load system control; (c) Truck being loading with proppant to transportto the wellsite.

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Neuquén. A second phase of the project will add 3 more silos, bringing the total storage plant capacityto 4,800 ton/10.4 million lbm.

Satellite Storage Center This alternative was evaluated and implemented to improve on-time deliveryand minimize transport distance. Logistics planning is necessary to execute an efficient job. A secondarystorage center is located at Añelo, 40 miles from the main VM activity. This storage center has a smallstorage capacity (1,200 ton/2.6 million lbm) and a simpler load system (Fig. 10). Another alternativewould be a smaller and simpler satellite center that uses a conveyor belt to unload large bags into bulktransport units; this option could be located closer to the field.

The main advantages of this type of center are that they can be relocated and moved closer to thewellsite to improve logistic time requirements, and they can be used for specific mesh types and smallvolumes of proppant.

Bulk Transport Unit An important part of this process a fleet of bulk transport units (pneumatic bulktrailer) built by an international supplier in Argentina. During 2014 and 2015, 10 units were built for thispurpose (Fig. 11). Each unit has a 60,000 lbm capacity and pneumatic unload capability (45 min. per truckto unload), which allows a proppant to be loaded into a storage unit in location in an expedited and safemanner. This eliminates issues with proppant accumulation in large bags on location, reducing thefootprint and personnel involvement in the process. Additionally, 3rd party agreements were developedfor renting additional units in case they are needed at any time.

Storage Unit at Wellsite The last part of the workflow was increasing the total storage capacity of thewellsite to improve efficiency. At the beginning of the unconventional operations in Argentina (2011), thiscapacity was 1.0 million lbm (4 storages units with 250,000 lbm capacity each). Current capacity wasincreased up to 3.8 million lbm (7 units of 400,000 lbm each and 4 units of 250,000 lbm each). Additional

Figure 10—(a) Satellite storage center and warehouse; (b) Loading platform for new bulk trucks.

Figure 11—Bulk transport unit fleet at wellsite with pneumatic unload system in back of the units.

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T-belt conveyor equipment was needed to collect and transport the proppant from the storage units to thefracturing fluid blender unit. Typical treatments use at least three types of mesh of proppant, which is oneof the reasons several storages units are necessary. For an efficient operation, loaded units for at least twofracture stages are necessary. Fig. 12 presents the layout at the wellsite and storage units on location.

Case History At the beginning of 2014, an operator began to drill a group of shale gas wells in VacaMuerta. The first project to implement the new proppant management model included 2 location pads with3 horizontal wells each. These 6 wells included a total of 64 fracturing stages, requiring 24 million lbmof proppant divided into three different meshes (70/140 � 6.2 million lbm, 40/70 � 14 million lbm, and30/60 � 3.8 million lbm). An integrated operational and logistic team was tasked with supply chain andlogistic planning (Fig. 13).

Figure 12—(a) Layout, storage unit, and bulk transport fleet; (b) Actual operation; (c) Storage units (5) at wellsite.

Figure 13—New proppant management model applied for two well pads (3 horizontal wells each pad).

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First, the amount of proppant required per day at the wellsite to perform two fracturing stages wasdetermined to be 1,210,000 lbm. The next step was to develop a plan to achieve this goal

Proppant Suppliers The type and volume of different proppants and their suppliers was identified, thenthe best option to import the proppant to the country was evaluated. The decision was made to work withtwo ports, Buenos Aires and Bahia Blanca. Finally, Bahia Blanca port was used for the supplier with thehigher volume of proppant (ceramic 40/70 and 30/60) and for the short distance to transport the productto the storage centers. The second port used was Buenos Aires for the other supplier (white sand 70/140mesh).

Storage Center A second part of this planning was developing a strategy for storing these proppants,considering the different amounts of proppant according to the mesh. It was decided to store the 40/70mesh in the storage plant in Neuquen city because of the high capacity (6.5 million lbm). This meantfilling the silo capacity 3.6 times. A satellite storage center was located at 30 Km from the wells (Añelocity), for storing and loading the other two meshes, which were transported from Buenos Aires and BahiaBlanca port.

Delivery Finally, a fleet of 20 bulk transport (sand trucks) were scheduled and coordinated from twostorage centers to the wellsite, to provide the amount of proppant for each mesh in a faster and safemanner. For this logistic item, renting additional bulk transport units was necessary.

As was presented and discussed above, an important improvement for proppant supply chain andlogistics has been developed over the last six years as a result of the continuous growing activity in VacaMuerta. A complete proppant management model has been developed and implemented to improvedelivery time, to increase the amount of proppant available at the wellsite, and to improve safety. Themain changes observed over the last year were more evident at the storage center and wellsite (Fig. 14).Future improvements will be made in bulk vessel transport or bulk rail transport, with the intention of amore cost effective system. Developing proper proppant logistics is a key factor to sustainable uncon-ventional developments.

Figure 14—Proppant logistics evolution in the last years.

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Laboratory Test for Local White SandBecause of continuous activity increases around the world and the exploration of new reservoirs(unconventional), there is a constant demand for proppant. This demand drives the search for alternatives,from natural sand or man-made proppants. Several authors have documented their studies: Kothamasu etal. (2012a) working with samples of white and brown sand from India and Saudi Arabia; Kamat et al.(2011) performed the same test for Malaysian sand; and Kothamasu et al. (2012b) explored the alternativeof ceramics manufactured in different regions in the eastern hemisphere. More recently, Peñaranda andLanza (2014) presented a detailed report about Argentinian local sand.

The API/ISO standards for evaluating proppant are primarily quality control procedures. The five mainstandards determining the proppant quality include sieve analysis, crush resistance, sphericity androundness, acid solubility, and turbidity.

In this section, local sands from three places in Argentina are analyzed with the intention of evaluatingtheir use in hydraulic fractures. A total of 13 samples were evaluated. Six local suppliers (identified asLS-1 to LS-6) provided white sand samples, but only two of them (LS-2 and LS-3) provided all three meshsizes (40/70, 30/50 and 20/40). These proppants were compared with global suppliers (GS), and theproppants were evaluated using the five API/ISO standards.

Sieve AnalysisParticle-size distribution is important because it determines the proppant packing inside the fracture,which in turn affects the fracture conductivity. This is one of the primary criteria used for quality controltesting of proppant. Table 4 shows the test results for all the proppant, classified by proppant mesh andsupplier.

Table 4—Sieve analysis data comparison of different local sand, % retained (* designates 30/70 mesh sample, otherwise 30/50).

Proppant size Sieve size GS LS-1 LS-2 LS-3 LS-4 LS-5 LS-6

40/70

30 0.0 0.0 0.07 0.0 0.01 0.02

40 1.66 2.77 0.30 3.89 0.03 0.30

50 69.52 51.19 53.25 41.18 41.67 18.15

60 17.73 30.60 24.20 29.44 43.08 45.15

70 9.63 12.74 19.06 24.73 6.36 32.47

100 1.00 0.19 2.96 0.36 7.65 3.85

Pan 0.46 2.51 0.16 0.40 1.09 0.01

30/50 and 30/70*

20 0.0 0.0 0.0 0.0 0.0 0.0

30 0.89 6.58 0.25 0.01 0.26 0.02

40 23.59 63.20 31.93 84.29 80.40 0.03

45 47.69 28.76 32.73 15.41 12.10 4.85

50 26.69 1.44 22.07 0.28 6.60 13.30

60* 45.15

70 0.94 0.02 12.11 0.0 0.54 32.47

100* 3.85

Pan 0.20 0.0 0.91 0.01 0.10 0.01

20/40

16 0.0 0.0 0.0 0.0

20 0.81 0.44 0.41 0.3

30 40.62 46.56 37.04 26.30

35 38.84 50.08 56.45 42.90

40 18.24 2.28 6.05 30.0

50 0.96 0.20 0.05 0.40

Pan 0.53 0.42 0.0 0.10

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According to ISO 2006, a minimum of 90% of the tested proppant sample shall pass the most coarsedesignated (or first primary) sieve screen and be retained on the most fine designated (or second primary)sieve screen. Not over 0.1% of the total tested proppant samples shall be larger than the first sieve screensize in the sieve stack specified, and not over 1.0% of the total tested proppant sample shall be smallerthan the last designated sieve screen size. Table 5 presents a summary and indicates in red the proppantdata that did not achieve the values required, which occurred for LS-2 (40/70 and 30/50), LS-5 (40/70 and30/70), and LS-6 (40/70).

SG and Bulk DensityThe SG is the ratio of the absolute density of the proppant with respect to fresh water. The bulk densityis the mass of the proppant divided by the volume of the proppant including pore spaces. A comparisonof the bulk density and SG of the LS proppant with the GS proppant is shown in Table 6. All the valuesare very similar.

Sphericity and RoundnessThe particle shape parameters that are useful for visual evaluation of sand are sphericity and roundness.Sphericity measures how close an object approaches the shape of a sphere and is an indication of how thegrains will pack inside the fracture. Roundness measures the relative sharpness of the particle’s cornersor edges. The most widely used method of determining roundness and sphericity for the characterizationof proppants is the use of the Krumbien/Sloss chart (ISO 2006). Ceramic proppants and resin-coatedceramic proppant shall have an average sphericity of 0.7 or greater and an average roundness of 0.7 or

Table 5—Sieve analysis data comparison of different local sand, % retained (* designates 30/70 mesh sample, otherwise 30/50).

Proppant size Sieve size GS LS-1 LS-2 LS-3 LS-4 LS-5 LS-6

40/70

30 0.0 0.0 0.07 0.0 0.01 0.02

40-70 98.54 97.30 96.81 99.24 91.14 96.07

100 1.00 0.19 2.96 0.36 7.65 3.85

30/50 and 30/70* 20 0.0 0.0 0.0 0.0 0.0 0.0

30-50/60* 98.86 99.98 86.98 99.99 99.36 96.09

70-100* 0.94 0.02 12.11 0.0 0.54 3.85*

20/40

16 0.0 0.0 0.0 0.0

20-40 98.51 99.36 99.95 99.50

50 0.96 0.20 0.05 0.40

Table 6—Specific gravity and bulk density data comparison of different local sand samples (* designates 30/70 mesh sample, oth-erwise 30/50).

Supplier

40/70 30/50 and 30/70* 20/40

SG B. Density (gm/cc) SG B. Density (gm/cc) SG B. Density (gm/cc)

GS 2.69 1.54 2.62 1.63 2.67 1.53

LS-1 2.55 1.46 2.70 1.54

LS-2 2.63 1.54 2.75 1.51 2.64 1.58

LS-3 2.54 1.71 2.54 1.73 2.86 1.57

LS-4 2.64 1.57 2.66 1.66

LS-5 2.63 1.58 2.64* 1.64*

LS-6 2.63 1.53

SPE-180818-MS 15

greater (ISO 2006). All other sand/proppants should have an average sphericity of 0.6 or greater and anaverage roundness of 0.6 or greater (ISO 2006).

To determine sphericity and roundness, 30 sand grains were picked randomly from the sample andwere classified. The results are presented in Table 7, and images of the global supplier (GB) and somelocal supplier samples of 40/70 mesh size products are presented in Fig. 15.

In general, all the sand samples for different mesh sizes presented very good values for sphericity, 0.7or 0.8, but that was not the case for roundness; several samples presented values of 0.5. Only LS-3presented a consistent value for these indicators for all the mesh.

Acid Solubility and TurbidityAcid solubility determines whether the proppant is suitable to be used in applications where it can comein contact with acid. The presence of acid-soluble impurities, such as carbonates and feldspars iron oxides,can weaken the proppant in an acidic environment and can reduce the proppant-pack permeability. Thesolubility is measured by calculating the amount of mass dissolved in 12:3 HCl:HF acid. According to ISO2006, for proppant (sand), the values should be less than 2% for mesh sizes between 6/12 and 30/50, and3% for mesh sizes between 40/70 and 70/140.

Turbidity determines the amount of suspended particles of fines present and should be as low aspossible. The turbidity of these proppants was measured by a spectrophotometer. The required values are250 formazin turbidity units (FTU) or less, according to ISO 2006. Table 8 presents the results for all testsperformed.

Table 7—Sphericity and roundness data comparison of different local sands.

Supplier

40/70 30/50 and 30/70* 20/40

Sphericity Roundness Sphericity Roundness Sphericity Roundness

GS 0.70 0.70 0.70 0.70 0.70 0.70

LS-1 0.70 0.50 0.70 0.50

LS-2 0.70 0.50 0.70 0.50 0.70 0.50

LS-3 0.70 0.70 0.70 0.70 0.70 0.70

LS-4 0.70 0.50 0.70 0.70

LS-5 0.80 0.50 0.80* 0.60*

LS-6 0.80 0.70

Figure 15—Samples of global supplier and different local suppliers (40/70 mesh).

16 SPE-180818-MS

In general, all the sand samples for each different mesh size failed tests of solubility; only two samplesachieved the values required for 40/70 mesh: LS-5 and LS-6. For turbidity, four samples failed: 40/70mesh for LS-2, LS-5, LS-6 and 30/70 mesh for LS-5.

Crush ResistanceThe crush resistance of the proppant sample indicates its compressive-strength capacity. The test evaluatesthe maximum stress to which the proppant should be subjected under downhole conditions. This is oneof the most important criteria in proppant selection. According to the ISO 2006 standard, the finesgenerated should not exceed 10%, irrespective of the sand size. This test is performed with a 4 lbm/ft2

areal concentration. For manmade proppant, the recommended testing range is 5000 to 15000 psi, and forfracturing sand, the range is 2000 to 5000 psi.

Considering the calculated closure stress (Fig. 2c) for several unconventional formations in Argentina,these values are in the range of 1000 to 5000 psi. The crush test to evaluate these proppants was performedat two pressures, 4000 and 5000 psi. Fig. 16 presented the result as ISO 2006 at the pressures indicatedpreviously. With the intention to test the proppant crush resistance at a more realistic downhole conditionfor these unconventional applications, the same test was performed at a lower proppant concentration (1lbm/ft2). The limit of 10% of fines generated is indicated with a red line (although this is not an ISOstandard comparison).

Finally, Table 9 presents the maximum stress for each proppant and mesh at 4 and 1 lb/ft2. In somecases, it was necessary to perform a test at 3,000 psi due the percentages of fines obtained in test at4,000-5,000 psi. The proppants that decrease the maximum stress that the material can withstand whentested to less proppant concentration are identified in red. In general, all the local white sand is 1K or 2Kless than the global source proppant data included in Table 9.

Table 8—Acid solubility and turbidity data comparison of different local sand.

Supplier

40/70 30/50 and 30/70* 20/40

Ac. Solubility Turbidity Ac. Solubility Turbidity Ac. Solubility Turbidity

GS 2.3% 36 1.8% 31 1.9% 64

LS-1 4.0% 47 6.2% 65

LS-2 10.2% 667 10.6% 68 8.2% 50

LS-3 4.8% 15 4.6% 66 6.6% 21

LS-4 5.8% 89 7.3% 89

LS-5 2.9% 445 2.6%* 340*

LS-6 2.8% 350

SPE-180818-MS 17

DiscussionAfter analyzing all the information obtained in these tests, one can conclude that local sand fromArgentina is generally non-API/ISO qualified proppant. Improvement opportunities in the manufacturingprocess of the suppliers exist, mainly in the classification, screening, and distribution of the meshes (sieve

Figure 16—Crush resistance data comparison of different local sand samples at 4000 and 5000 psi and 4lb/ft2 and 1lb/ft2 (more realisticunconventional reservoir condition).

Table 9—Crush resistance data comparison of different local sand samples.

Supplier

40/70 30/50 and 30/70* 20/40

4 lb/ft2 1 lb/ft2 4 lb/ft2 1 lb/ft2 4 lb/ft2 1 lb/ft2

GS 6K – (4.67%) 6K – (6.87%) 6K – (7.07%) 6K – (8.84%) 5K – (8.96%) 5K – (9.97%)

LS-1 4K – (6.81%) 4K – (7.11%) 4K – (9.15%) 4K – (9.78%)

LS-2 5K – (9.86%) 5K – (9.20%) 5K – (9.06%) 4K – (9.11%) 4K – (8.20%) 4K – (9.83%)

LS-3 5K – (6.38%) 5K – (7.15%) 4K – (9.30%) 4K – (9.93%) 3K – (7.02%) 3K – (9.68%)

LS-4 4K – (9.95%) 4K – (9.48%) 3K – (3.20%) 3K – (6.90%)

LS-5 5K – (7.89%) 4K – (8.70%) 5K* (8.89%) 4K* (6.37%)

LS-6 4K – (6.53%) 3K – (9.10%)

18 SPE-180818-MS

analysis) and in the cleaning of the material (turbidity). Das et al. (2013) explained the importance for acorrect quality control process with the intention of setting up a local supplier to compete in the globalmarket. There are other aspects that are typical to the nature of the deposits or the grain (quartz), such asroundness and acid solubility. Kamat et al. (2011) and Peñaranda and Lanza (2014) observed the sameresult about roundness for local sand.

However, good results for crush resistance were obtained, in general 1,000 to 2,000 psi less than theglobal supplier evaluated. For the test performed at low proppant concentrations (1 lbm/ft2), it was clearthat most samples maintain the classification (compression rating value). Only one group of themexperienced a decrease in compression rating value.

An alternative for improving the crush resistance could possibly be coating natural sand, as wasmention by these authors:

● Kamat et al. (2011) proposed some adjustments through coating natural sand with resin materialafter a complete and detailed evaluation of natural sand from Malaysia.

● Nguyen et al. (2014) concluded after laboratory tests, that low-quality sand provided comparableconductivity performance to that of high-strength proppant in proppant-free channel testing (sandonly in dispersed pillars in closed fractures). These pillars were created using a specified weightpercent concentration of an on-the fly coating of curable resin (a premixed two-component epoxyresin system) to form a uniform coating on the grain surfaces. The low-quality sand used consistedof particulates that did not meet API standard requirements for conventional fracturing treatmentbecause of their high angularity, low crush strength, and wide particle-size distribution. Addition-ally they might have contained small quantities of mineral particles other than quartz. Examplesof this sand included desert sand, beach sand, or a combination of lower-quality brown sand ofdifferent sizes.

● Stegent et al. (2010) presented an example from Eagle Ford Shale, in which the desired proppantwas not available (ceramics) and a specific surface modification agent (SMA) added to naturalsand substrates was substituted during the hydraulic fracture. This alternative provides an efficientlow-cost alternative to manmade proppant especially during times of supply shortages. This SMAcan be used to upgrade proppant performance.

ConclusionsThe strength of proppant is a significant concern in the design of hydraulic fractures. A detailed analysisperformed for Lajas, Punta Rosada, Mulichinco and Vaca Muerta formation showed that the closure stresson proppant can vary between 1,000 to 5,000 psi.

Particular characteristics were observed about the amount, type, and mesh sizes of proppant fordifferent tight or shale reservoirs in Argentina. Typically in Vaca Muerta formation, 3 to 4 mesh sizes ofnatural sand and ceramic proppants in various combinations (low and medium density) are used, and theamount of proppant varies from 2 million lbm in vertical wells to 8.5 million lbm in horizontal wells. Inother Neuquen tight reservoirs, some differences exist, but in general, 2 mesh sizes are used, with one typeof proppant (natural sand or ceramics), and the amount of proppant per well varies according to theformation, from 1.45 million to 1.8 million lbm in a multi-stage fracturing stimulation of a well.

A new model of proppant management was implemented to improve the efficiency of this type ofcompletion in shale plays. A new proppant storage plant, satellite storage center, and new bulk transportunits were the main changes implemented in the Neuquen basin. Additional improvements in relation toa new port (Bahia Blanca) and the amount of proppant transported by vessel were also implemented.Proper planning to execute field operations for a large volume of proppant has been documented.

Argentinian natural sand was evaluated and samples tested were determined to be non-API proppant.Several improvements will be required for the natural sand to qualify as API proppant, but the nature of

SPE-180818-MS 19

the proppant has shown non-API roundness values. However, very good values for crush resistance wereobtained for the range of closure stress on proppant identified in Neuquen unconventional formations. Ingeneral, these proppant samples were 1 or 2 kpsi lower stress qualified than the global source proppant.For the tests performed at low proppant concentration (1 lbm/ft2), it was clear that most samplesmaintained the strength classification observed at 4 lbm/ft2; only a group of them decreased in strengthrating.

According to other authors’ work mentioned earlier, it could be possible to use local natural sand bymodifying it for some of the unconventional reservoirs where a higher closure stress is identified. Onealternative to improve the crush resistance could be coating natural local sand. These options will beexplored in future tests.

Finally, all the topics covered in this publication have an important role in unconventional projects ofreducing the cost of a proppant placed in storage units at a wellsite. The amount, the type and sieve sizeof proppant, the simplicity of the operation (number of mesh sizes used), a proper supply chain andlogistic plan, the wellsite resources available, a safe operation, and a more cost-effective proppantalternative are each key factors to achieving a sustainable unconventional project development.

AcknowledgmentsThe author thanks Halliburton for the permission to publish this paper. Special thanks are extended toHernan Carbonell (proppant logistic), Federico Kovalenko (case history), Dario Soto and Pascual Tarasio(retired) for laboratory work, and Mariano Garcia for his comments and suggestions.

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