When injecting proppants into fractures, the processes of proppant migration, distribution and settlement are highly dependent on the fracture surface roughness and the complexity of the fracture. As a result, there are three different types of proppant distributions that can be expected within fractures: (1) partial monolayer proppant arrangement, (2) uniform monolayer proppant arrangement, and (3) multilayer proppant arrangement. In a partially proppant-distributed fracture, an individual proppant is subjected to significantly high single-point loading at the proppant-proppant or proppant-rock contact. The probability of the occurrence of either proppant crushing or embedment is high. Hence, in this section, we analyse the behaviour of a single proppant upon subjection to in-situ stress conditions by considering the impact of the type of proppant, the type of formation rock, and effect of realistic reservoir environments. A series of DEM simulations using calibrated proppant-rock models was performed to analyse the response of a single proppant placed on the rock surface and subjected to increased stress environments. The set-up of the numerial model in the DEM simulations is shown in Fig. 6. To reduce the computational cost, the thickness of the simulated rock was limited to 2 mm.
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Fig. 6DEM simulation set-up to analyse single proppant interaction with formation rock
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3.1
Single proppant interaction with sedimentary-based siltstone formation3.1.1
Crushing and embedment response of proppants with increasing stress levels$${\text{Proppant embedment = Total deformation {-} Proppant deformation {-} Rock deformation }}$$
(1)
In this section, the effect of proppant type on interactions with dry-intact siltstone sedimentary-based formations is analysed. Figures 7a and b represents the variation of compressive stress with numerical time-steps for ceramic and frac-sand proppants, respectively. In this analysis, numerical time-steps were used as the variable for the x-axis, instead of axial displacement/strain, to provide better comparative visualisation of the variation of compressive stress. In addition, to accurately study the mechanical response of individual ceramic and frac-sand proppants, the embedment induced as a result of increasing stresses was calculated using Eq. 1, and the results are presented in Fig. 7c. In Eq. 1, the proppant deformation and rock deformation refer to distinct deformation undergoing within proppant and rock, respectively, as a result of the increasing stresses. Thus, to calculate these two parameters, numerical simulation tests were performed on the individual proppant and rock, separately and their respective deformations were recorded with increasing stresses. Then, proppant embedment was calculated by deducting respective proppant deformation and rock deformation from the total deformation at each loading level (total deformation is the deformation we record when conducting DEM simulation of a single proppant-rock test). Similar embedment analysis was adopted by [67] to accurately detect the embedment with load increments.
Fig. 7a Compressive stress variation with numerical steps for ceramic proppant-intact dry siltstone formation, b compressive stress variation with numerical steps for frac-sand proppant-intact dry siltstone formation, and c comparison of proppant embedment and compressive stress for different proppant types on intact dry siltstone formation rock
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According to Fig. 7a and b, the ceramic proppant shows a slow stress growth with numerical time steps. However, the frac-sand proppant reaches the failure stress rather rapidly. This behaviour of ceramic proppants is mainly due to the significant plastic deformation which occurs as a result of the dominant proppant embedment mechanism. However, in frac-sand proppant, the stress response is more linearly variable with numerical time-steps due to the dominant crushing process of frac-sand proppant when interacting with siltstone formations at increasing stress levels. According to the results depicted in Fig. 7c, both proppants tend to show an increase in proppant embedment with stress increment. In addition, the results reveal that the ceramic proppant shows a significantly high proppant embedment at each stress level in comparison with frac-sand proppant. According to Fig. 7c, at stress levels of 10, 20, 30, 40, and 50 MPa, ceramic proppant shows a proppant embedment of 224, 244, 257, 277, and 323 µm, respectively. However, at 10, 20, and 30 MPa stress levels, only a minor embedment is shown by the frac-sand proppant; 27 (88% lower than the ceramic proppant at a similar stress level), 38 (84.3% lower), and 56 µm (78.1% lower), respectively. Moreover, for ceramic proppants, a higher embedment-stress gradient can be observed at lower stress levels; however, the rate of proppant embedment declines at higher stresses. Although frac-sand shows significantly lower proppant embedment than ceramic proppants, frac-sand proppants have no potential to withstand any compressive stress beyond 35 MPa, as the frac-sand proppants undergo a significant amount of crushing. Nevertheless, no crushing of ceramic proppant is experienced at increasing stress levels upon interaction with the dry-intact siltstone rock formation. However, the following section provides a detailed analysis of proppant-rock fracture initiation, fracture propagation, and fracture coalescence mechanisms when undergoing sand proppant crushing and ceramic proppant embedment while capturing proppant-rock deformation. These findings are consistent with the numerical findings presented by Zheng and Tannant [67] and Zheng et al. [67].
3.1.2
Formation rock damage and fracture evolution during ceramic proppant embedmentThe DEM simulation of a single proppant-rock response to increasing stress levels provides a novel approach to understanding the granular level fracture evolution mechanism during proppant embedment. The evolution of the proppant embedment of ceramic proppants with increasing stress conditions is presented in Fig. 8. In the DEM simulation, a crack or fracture visualised as a disc is generated when the bonding between two individual particles breaks. Here, tensile cracks occurring in the proppant are shown by a red disc, while tensile and shear cracks occurring within rock are shown by blue and pink discs, respectively. At minor stress levels (0.6 MPa), ceramic proppants show the initiation of a small number of tensile cracks at the contact location with the top loading platen. In addition, the generation of tensile dominant fractures can be observed in the siltstone formation, which initiates from its contact interface with the proppant. With the increment of the stress level to 10 MPa, the embedment of ceramic proppant in the siltstone rock causes rock particle spalling, which is typical when the rock surface is indented with high-strength proppants. In addition to fracture aperture reduction due to proppant embedment, the phenomenon of fines generation as a result of rock particle spalling might further reduce fracture conductivity by blocking the path of oil/gas flow [25]. With the increase in ceramic proppant embedment with the increment of stress-levels, the tensile dominant fractures initiated at the proppant-rock contact interface tend to propagate gradually. As illustrated at the fracture evolution figure at 50 MPa, a number of fractures have propagated from the proppant-indented location. Importantly, beyond 50 MPa stress levels, several major fractures coalesce, causing significant damage to the proppant-embedded rock formation. Although ceramic proppant shows an embedment of 323 µm at only 50 MPa, beyond this stress level, the rock surface cannot take any further increase in loading due to the significant damage caused to the rock formation as a result of secondary fracture initiation, propagation and coalescence. Upon reaching this damage stress level (beyond 50 MPa in this instance), ceramic proppant undergoes further embedment at a higher rate until it fully indents into the rock surface. This can be clearly observed in Fig. 7c, as upon reaching the 50 MPa stress level, the embedment-stress gradient of ceramic proppant suddenly increases. Importantly, the initiation and propagation of ceramic proppant embedment-induced secondary fractures in siltstone formations have been revealed in our previous studies [5], 5]. Some of the experimental findings obtained from Bandara et al. [5] are presented in Fig. 9. Figure 9a shows a computed-tomography scanned reconstructed image of secondary fracture initiated and propagated at a proppant-embedded location. Furthermore, Fig. 9b illustrates a 3D-profilometer scanned image at a ceramic proppant-embedded location, where a fracture has initiated upon partial embedment of ceramic proppant in a siltstone formation. The process of secondary fracture initiation and propagation as a result of proppant embedment is mainly due to the layered crystal structural orientation of the kaolinite minerals of siltstone. It has been identified that during the process of proppant embedment, existing hydrogen and van der Waals bonds of layered kaolinite minerals of siltstone specimens collapse and generate fractures [56, 41]. These findings further validate the results obtained in the current DEM simulation of the single ceramic proppant-siltstone rock response to increasing stress levels. Moreover, the findings in Fig. 8 reveal that during the ceramic proppant-siltstone rock response to increasing stresses, ceramic proppant does not show a tendency to undergo any crushing. However, small numbers of tensile fractures can be observed near the contact interface between the top-loading platen and the proppant.
Fig. 8Fracture evolution pattern of numerically-simulated ceramic and frac-sand proppant when interacting with dry-intact siltstone formation
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Fig. 9a Computed-tomography scanned reconstructed image of secondary fracture initiation and propagation at proppant embedment location, and b 3D-profilometer scanned image at ceramic proppant embedded location [4]
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3.1.3
Fracture evolution during frac-sand proppant crushing and embedmentIn addition, Fig. 8 illustrates the detailed fracture evolution during sand proppant crushing with increasing stress levels. According to the results, tensile dominant fractures within the sand proppant can be observed near its contact location with the top platen at a very early stress level of 0.5 MPa. However, with the gradual increment of stress levels, more tensile dominant fractures initiate within the sand proppant at both its contact interfaces with the top platen and the rock. With the initiation of cracks, at around 57% of the peak load (21 MPa), tensile fractures tend to propagate within the frac-sand proppant. At 90% of the peak failure stress (33 MPa), a major meridional crack (diametrical crack) in the sand proppant initiates from the upper loading platen and propagates towards the rock. As the sand proppant reaches this stage, further increment in loading causes a major diametrical crack to coalesce with minor fractures causing significant damage to the proppant microstructure. According to Fig. 8, at the 37 MPa stress level, a number of cracks have propagated from the major diametrical fracture, ultimately leading to catastrophic proppant crushing failure.
3.2
Single ceramic and frac-sand proppant interaction with granite formation3.2.1
Crushing and embedment response of proppants with increasing stress levelsGranite is the most abundant rock type in geothermal formations [25], which can be enhanced with hydraulic fracturing with proppants. Therefore, in this section, the behaviour of ceramic and sand proppants interacting with granite formations under the influence of increasing stress conditions is analysed in detail. Figure 10a and b provides the single proppant compressive stress response with increasing numerical time-steps for ceramic and frac-sand proppants, respectively. Similar to the findings observed when interacting with siltstone formations, slower stress growth in ceramic proppants is observed compared with frac-sand proppants when proppants are subjected to compression in granite formations. Importantly, according to Fig. 10a, with the increase in loading, ceramic proppant shows a number of additional peak stress points upon reaching its preliminary failure at 123 MPa. According to the results, the ceramic proppant shows initial peak stress at 123 MPa and suddenly drops to 3 MPa, followed by another stress increment curve. In addition, the second load increment curve of the ceramic proppant follows a saw-tooth behaviour in the proppant stress-numerical steps response. This is mainly due to the breaking of asperities or the disintegration of the ceramic proppant during the loading process. Interestingly, even after preliminary failure at 123 MPa, ceramic proppant is subjected to further strength increment up to 143 MPa, later followed by full crushing of the proppant. However, for the frac-sand proppant, the loading curve follows a rapid and linear stress response followed by a rapid and catastrophic crushing process at a very low compressive stress of 40 MPa (Fig. 10b). Although both ceramic and frac-sand proppants show a dominant proppant crushing mechanism upon interaction with granite formations, proppant embedment also occurs simultaneously with increasing stress levels. Figure 10c illustrates the proppant embedment variation of ceramic and frac-sand proppants with stress levels calculated with the aid of Eq. 1. According to Fig. 10c, the embedment observed during the first loading curve of ceramic proppant and frac-sand proppant follows a similar embedment increment with each stress level. According to the results, frac-sand proppant shows an embedment of only 60.4 µm at its maximum load capacity of 40 MPa, and frac-sand proppant undergo severe crushing beyond this stress level. In addition, ceramic proppant shows an embedment of only 121.5 µm at a very high-stress level of 120 MPa during its first loading curve. However, upon reaching 120 MPa stress levels, both ceramic proppant and the proppant contacting granite interface may be expected to undergo severe damage. This can be predicted due to the higher embedment-stress gradient depicted by the ceramic proppant during its second loading curve. According to the results, during the second loading curve exhibited by ceramic proppant, embedment values of 293.5 (368% increment compared to the embedment observed in the first loading cycle), 404.3 (407%), 459.1 (388%), 536.8 (388.8%), 558.6 (359.4%), and 587.6 µm are obtained at stress levels of 40, 60, 80, 100, 120, and 140 MPa, respectively. In the following section, a detailed analysis of the evolution of ceramic and frac-sand proppant crushing and embedment in granite formations with increasing stress levels is provided with the assistance of numerically-modelled DEM simulations.
Fig. 10a Compressive stress variation with numerical steps for ceramic proppant-granite formation, b Compressive stress variation with numerical steps for frac-sand proppant-granite formation, and c comparison of proppant embedment and compressive stress for different proppant types in granite formation rock
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3.2.2
Fracture evolution during ceramic proppant crushing and embedmentIn this section, the mechanisms of ceramic proppant embedment and crushing, fracture generation, propagation, and coalescence during proppant embedment and crushing under increasing stress conditions are discussed. Figure 11 shows the DEM-simulated fracture evolution results for ceramic proppant interaction with the granite formation. According to Fig. 11, during the initial loading stage, tensile fractures appear near the proppant-top loading platen contact interface. In addition, the gradual and slow indentation of ceramic proppant into the granite formation during the initial loading phase induces shear fractures near the proppant-rock contact area. The generation of shear fractures on the granite formation rock upon the interaction of ceramic proppant may be due to ceramic proppant rotation and sliding on the stiff granite surface. This ceramic proppant behaviour of sliding on stiff granite formations can be clearly seen in the first row of Fig. 11. As described in Sect. 3.1.1, a higher ceramic proppant embedment of 323 µm was observed in soft siltstone formations even at very low stress of 50 MPa. However, due to the stiff, brittle nature of granite formations, even at very high stress of 100 MPa, ceramic proppant embedment of only 110 µm was detected. Nevertheless, at higher stress levels up to 100 MPa, constant interaction between high-strength ceramic proppant and very stiff granite rock leads to significant asperity changes within the proppant as well as within the rock surface. To accurately visualise the asperity damage in the proppant assembly, the DEM results of the fracture propagation pattern of the proppant are presented in the third and fourth rows of Fig. 11. According to the results, upon reaching 100 MPa, the cluster of particles starts to fragment. Further increment of loading up to 120 MPa causes additional tensile fractures to initiate from the top and bottom contact regions of the ceramic proppant. Importantly, upon reaching 123 MPa, rock particle spalling from the granite surface can be detected. Similar to the findings described in Sect. 3.1.2, with the initiation of particle spalling from the rock surface, ceramic proppants tend to embed into the formation at a higher rate, eventually causing significant damage to the granite near the contact with the ceramic proppant. The sudden unloading phase identified after reaching 123 MPa in Fig. 10a is due to the initiation of particle spalling from the granite surface. However, with the further increase in loading, the phenomenon of particle spalling increases substantially, leading to a rapid increment in the rate of proppant embedment, as detected in the second loading curve. In addition, simultaneously to the proppant embedment process, a significant increase in proppant fragmentation can be observed during the second loading curve, as illustrated in the fourth row of Fig. 11. Upon reaching 100 MPa during the second loading curve, a substantial number of tensile-dominant fractures can be seen near the top and bottom contact points of the ceramic proppant. However, further increase in loading up to 140 MPa permits the sudden propagation of distinct vertical split fractures converging from the top and bottom of the ceramic proppant contact points, making the ceramic proppants mechanically unstable to withstand any additional load.
Fig. 11Fracture evolution pattern of numerically-simulated ceramic proppant when interacting with granite formations
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3.2.3
Fracture evolution during frac-sand proppant crushingAs described in Sect. 3.2.1, frac-sand proppants undergo a dominant crushing mechanism in granite formations when exposed to elevated stress conditions, which is shown in Fig. 12. According to the results, upon initial compression of sand proppant, stress concentrates at the proppant contact points with top loading platen and rock that act as flaw initiation zones [11]. As a result, a significant number of tensile-dominant fractures initiate within the sand proppant assembly, even at low stress of 20 MPa. Further increase in stress to 30 MPa results in major diametrical cracks propagating and converging from the top to the bottom of the sand proppant assembly. Moreover, as the sand approaches its failure strength, sand granules start to form fractures with the rapid propagation of multiple cracks. On the verge of sand proppant failure, two major fractures can be observed almost perpendicular to each other, with additional micro-cracks coalesced from the two tensile fracture planes. A similar fracturing mechanism was identified by Zhao et al. [64] by analysing the single sand fracture mechanism using X-ray micro-tomography (see Fig. 13). Note that the current DEM simulations were performed based on the assumption that sand proppants are perfectly spherical. The realistic fracturing mechanism of non-spherical sand particles may slightly differ in terms of the number of fragments created.
Fig. 12Fracture evolution pattern of numerically-simulated frac-sand proppant when interacting with granite formation
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Fig. 13Fracture patterns of sand particles subjected to compression [64]
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3.3
Single ceramic proppant interaction with saturated siltstone formations3.3.1
Impact of rock-saturation condition on mechanism of proppant embedmentAccording to the results reported in Sects. 3.1.1 and 3.2.1, the occurrence of proppant embedment is noteworthy even in dry siltstone and granite formations. In realistic hydraulic fracturing reservoir conditions, formation rocks are often exposed to various types of reservoir and fracture fluids over a long period. Therefore, in such circumstances, the impact of proppant embedment may be even critical and have a noteworthy impact on oil/gas recovery from sedimentary-based unconventional reservoir formations. Therefore, this section quantifies the effect of ceramic proppant embedment in siltstone formations exposed to different saturation conditions (30 days water-saturated siltstone, 30 days NaCl (25%) saturated siltstone, 30 days oil-saturated siltstone). DEM simulations of compressing a single proppant on a rock face were conducted to understand the influence of reservoir/fracture fluid saturation on proppant embedment. The simulation results under different saturation conditions are compared with the simulation results of dry-intact siltstone specimens with ceramic proppant. In this section, the type of proppants is limited to ceramic, as the effect of proppant embedment becomes critical when using ceramic proppant compared with less-stiff sand proppant. The embedment into formation rock by a single proppant was calculated using Eq. 1.
Figure 14a represents the embedment obtained from DEM simulations for different saturated siltstone formations with increasing stress levels. It is evident that regardless of the saturation condition, fracture/reservoir fluid saturation of siltstone formation rock has a significant impact on the increment of proppant embedment compared with dry-intact siltstone formation. A maximum ceramic proppant embedment of 613 µm was detected for water-saturated siltstone formation rock at 50 MPa stress level, while, under similar stress conditions, dry-intact proppant showed an embedment of only 323 µm. In addition, for both dry-intact and water-saturated siltstone formations, maximum stress-level to withstand embedment was 50 MPa. For 25% NaCl saturated and oil-saturated siltstone specimens, the maximum stress level that could withstand embedment further reduced to 25 and 20 MPa, respectively. Beyond the maximum stress levels, significant damage was experienced by the formation rock due to ceramic proppant embedment, and the formation rock is no longer able to withstand any further increase in stress. Proppant embedment in dry-intact siltstone formation shows a reduction in its increment rate upon reaching 10 MPa stress. In contrast, for the water-saturated, 25% NaCl-saturated and oil-saturated siltstone specimens, a higher incremental rate in proppant embedment can be detected with increasing stress levels. For instance, even at a very low confining stress of 20 MPa, high proppant embedment amounts of 323.9 (33% increment compared to embedment in dry-intact siltstone at 20 MPa), 426.1 (74% increment), and 625.7 µm (155.6% increment) are shown by water-saturated, 25% NaCl saturated, and oil-saturated siltstone specimens, respectively.
Fig. 14a Proppant embedment variation with siltstone saturation condition, and b siltstone Young&#;s modulus and UCS variation with saturation conditions
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During hydraulic fracturing, various forms of fracturing fluids can be injected to rock formations. These fluids include slickwater, cross-linked, visco-elastic surfactant, oil-based, acid-based, alcohol-based, emulsion-based, and form-based fluids [20, 54]. The interaction of formation rocks with injected fracture fluids can result in the softening of fracture surfaces and weakening of formation rock due to the reduction in the rock&#;s Young&#;s modulus [33]. Importantly, the effect of rock&#;s Young&#;s modulus on proppant embedment has been subjected to extensive study by a number of authors [2, 11, 67]. According to these authors, the decrease in Young&#;s modulus of a formation leads to a substantial increase in proppant embedment. Therefore, in order to accurately quantify proppant embedment with fracture fluid interaction in the current DEM analysis, Young&#;s modulus variations in calibrated siltstone assemblies are presented in Fig. 14b. In addition, the mechanical strength variation (unconfined compressive strength) of each calibrated saturated-siltstone formation is illustrated in the same figure. According to the results, the reduction in the Young&#;s modulus and the UCS of the calibrated saturated-siltstone show an inverse correlation to ceramic proppant embedment, consistent with the findings of Alramahi and Sundberg [2] and Zheng et al. [67]. In reality, siltstone saturation with different fracture/reservoir fluids can lead to several microstructural and mineralogical alterations in rock specimens. The experimentally-tested siltstone specimens used for the DEM calibration process in the present study have mainly kaolinite and quartz-rich mineralogical compositions. In addition, the experimentally-tested siltstone specimens have higher volume pore structures with porosities ranging up to 20%. Therefore, the saturation of siltstone specimens causes significant strength degradation to its microstructure, as clay minerals and cement materials interact with surrounding water bodies by means of absorption, ion exchange, and swelling mechanisms [63]. In addition, the existence of a large volume pore structure within siltstone specimens further accelerates fracture surface softening. Furthermore, the interaction of NaCl with the kaolinite and quartz minerals of siltstone leads to mineral corrosion, causing formation softening and strength weakening [16, 53]. Similarly, with the interaction of oil and siltstone, the organic compounds present in oil reduce siltstone&#;s mechanical stability due to chemical weathering [6].
3.3.2
Proppant embedment-induced formation rock damageIn this section, we evaluate proppant embedment-induced formation rock damage in saturated siltstone specimens. Figure 15 shows the DEM results of fracture damage in calibrated siltstone assemblies at their respective maximum failure stress. In addition, the tensile and shear fractures generated during proppant embedment-induced formation damage are separately recorded. Figure 16 represents the variation of tensile and shear fracture counts produced by DEM-calibrated rock assemblies under different saturation conditions. Similar to the findings reported in the previous sections, significant formation damage occurs in the process of proppant embedment, and the extent of formation damage is greater in saturated siltstone specimens than dry siltstone specimens. According to Fig. 15, in the DEM simulation with dry siltstone, proppant embedment at the maximum stress (50 MPa) shows a single major fracture generated from the proppant indented location, propagating to the rock model boundary. With the effect of saturation of siltstone specimens, fractures tend to propagate in multiple directions at the onset of the respective failure stress. In addition, the fractures propagated in multiple directions coalesce from the proppant-indented location, forming a fracture network within all the saturated siltstone specimens. Therefore, it is evident that asperity damage in saturated siltstone specimens is substantially greater, which can negatively affect oil/gas recovery. Moreover, according to Fig. 16, the total induced fracture count increases to , , in water-saturated, 25% NaCl saturated, and oil-saturated specimens, respectively, compared with dry siltstone specimens ( fracture counts). The higher fracture counts portrayed by oil-saturated siltstone specimens correlate to the higher embedment shown by the ceramic proppant even at a very low-stress level. In addition, the fracture mechanism illustrated by all the simulated siltstone specimens shows a tensile-dominant fracturing mode. The small number of shear fractures shown by all the specimens may result from frictional slip between fracture surfaces during fracture propagation and coalescence.
Fig. 15Fracture evolution pattern with proppant embedment for saturated siltstone formations
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Fig. 16Tensile and shear fracture count for DEM-simulated saturated rock formations
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It&#;s 4:00 am, there is a test in four hours. You still have to shower, make coffee, feed the dog, get the kids to school, and drive 45 minutes to the testing facility. That leaves you with 13 minutes and 27 seconds to understand proppants.
Don&#;t worry, there is only two things that you must know about proppants and why they work.
Done with at least 6 minutes to spare.
Bad news, the world of proppants can be a lot more complicated than that. Good news, you don&#;t actually have to take that test.
One of the more difficult things about hydraulic fracking is understanding what is actually happening several thousand feet under the ground. Cameras do not work under those harsh conditions, and you definitely cannot send someone down to watch.
The easiest and most cost effective way of understanding things we cannot see is to model key aspects of the environment below the surface of the Earth.
One test mimics the pressures of 2-3 miles of dirt, rocks and water, ISO/API&#;s Proppant Crush-Resistance Test. This puts the proppants under different pressures and checks proppants&#; resilience to these forces.
The test starts by prepping the proppants to make sure there are no particles smaller than a 200 US mesh screen. Then the sample of the proppant is placed onto a smooth steel plate within a cylinder. A piston is used to apply and hold specific pressures for two minutes. These pressures start at 2,000 PSI and step up every 1,000 PSI.
After performing the test, the proppants are sieved to see how many particles pass through the 200 mesh.
What does this show? Before the pressure was applied, the proppant sample was sieved, removing all particles smaller than 200 mesh. If any new particles pass through the 200 mesh sieve after the test, it was due to the proppant literally crumbling under the pressure. When the crushed, pulverized, and destroyed particles surpass 10% of total weight of the sample, the proppant is considered unusable at those pressures.
When the individual grains of the proppant crumble, break, and fail, they leave behind small broken glass-like pieces. These shards block the passage of the oil and gas through the proppant, not allowing the well to produce as much of the commodity as it could. Also, the irregular shape of the shards do not add any strength to the other proppants in the area. Meaning the other particles have to hold more weight. With the increased weight, the greater chance the other particles also crumble, break and fail. It becomes a feedback loop that causes less output in the real world.
Now enter microproppants. Microproppants are particles smaller than US Sieve 140 mesh. What else is smaller than US Sieve 140 mesh? US Sieve 200 mesh.
The ISO/API crush-resistance test removes would be microproppants before it can be evaluated. Making this test as-is, irrelevant to evaluate microproppants. The solution to adjusting ISO/API crush-resistance test would be to lower the sieve size to a US Sieve 270 mesh or 325 mesh depending on the microproppant.
Unfortunately, not everyone that makes decisions on the best proppant for their wells understands the ins and outs of this process. Those that depend heavily on ISO/API&#;s method to discern what is a good or bad proppant when looking at microproppants might miss out because of the bureaucratic nature of depending on specification sheets.
Another quagmire with microproppants as an emerging technology is silica flour. Silica flour is being pushed as a microproppant.
What is silica flour? Silica flour is where silica sand is crushed, pulverized, and destroyed in a milling process. Silica flour is the exact particle that ISO/API&#;s crush-resistance test looks for.
Silica flour fails at proppants&#; first two jobs of holding open the shale and allowing the petroleum to pass through it.
When evaluating possible microproppants, look for wholegrain products. Ask for ISO/API results for the microproppant. If there are no results, it shows that the microproppant cannot pass the tests at any capacity.
Microproppants are a new and exciting development in the oil and gas world, but be careful when deciding what to use for the horizontal wells.
The company is the world’s best ceramic proppant supplier supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.