Experimental Investigation of Proppant Flowback Phenomena Using a Large Scale 
Fracturing Simulator

Goel, Naval; Shah, Subhash

doi:10.2523/56880-ms

“…They observe that packs with width/grain diameter larger than 6 are inherently unstable. Goel et al's5 experimental results indicate that this ratio depends on closure stress, with higher values corresponding to lower closure stresses. All of the above analyses are based on simplified fracture models, where proppant beds are formed horizontally and gravity actually helps keep the proppant in place.Experimental results also show the presence of a critical flow rate through the pack above which the pack becomes unstable.…”

mentioning

confidence: 97%

Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

Daneshy¹

2004

Proceedings of SPE Annual Technical Conference and Exhibition

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TX 75083-3836, U.S.A., fax 01-972-952-9435.Abstract. The vast majority of industrial hydraulic fractures propagate in off-balance mode, where the fracture is not in a single plane, includes many shear fractures and branches, and is shorter and narrower than computed by existing models. Proppant transport, deposition and flowback in these fractures are also substantially different than for single fractures. Presence of shear fractures leads to formation of many randomly distributed tight proppant packs. Many of these are inherently unstable and serve as sources for proppant flowback. But they are also the source for fracture conductivity. Gravity causes formation of proppant beds. These are usually formed at the lower extremities of the fracture. Branches generally trap the proppant and are unlikely sources for flowback. They also add little to productive capacity of the fracture. And, some of the proppant in the fracture is loosely scattered inside it and is free to move when sufficient drag is exerted by fluid flow.The paper places special emphasis on proppant flowback and shows that the three requirements for its occurrence are motion initiation, motion maintenance and infinite conductivity along the return path. Gravity plays a very important role in this process, as does well completion. Tendency for equilibrium between reservoir fluid velocity and deposited proppant results in gradual decrease and eventually stoppage of proppant return at any given flow rate. This equilibrium can be disrupted by sudden increases in flow rate which then triggers instability and proppant flowback.Case histories from actual treatments illustrate and re-enforce the findings of the paper.

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Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

Daneshy¹

2004

SPE Annual Technical Conference and Exhibition

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TX 75083-3836, U.S.A., fax 01-972-952-9435.Abstract. The vast majority of industrial hydraulic fractures propagate in off-balance mode, where the fracture is not in a single plane, includes many shear fractures and branches, and is shorter and narrower than computed by existing models. Proppant transport, deposition and flowback in these fractures are also substantially different than for single fractures. Presence of shear fractures leads to formation of many randomly distributed tight proppant packs. Many of these are inherently unstable and serve as sources for proppant flowback. But they are also the source for fracture conductivity. Gravity causes formation of proppant beds. These are usually formed at the lower extremities of the fracture. Branches generally trap the proppant and are unlikely sources for flowback. They also add little to productive capacity of the fracture. And, some of the proppant in the fracture is loosely scattered inside it and is free to move when sufficient drag is exerted by fluid flow.The paper places special emphasis on proppant flowback and shows that the three requirements for its occurrence are motion initiation, motion maintenance and infinite conductivity along the return path. Gravity plays a very important role in this process, as does well completion. Tendency for equilibrium between reservoir fluid velocity and deposited proppant results in gradual decrease and eventually stoppage of proppant return at any given flow rate. This equilibrium can be disrupted by sudden increases in flow rate which then triggers instability and proppant flowback.Case histories from actual treatments illustrate and re-enforce the findings of the paper.

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Erosion by Proppant: A Comparison of the Erosivity of Sand and Ceramic Proppants During Slurry Injection and Flowback of Proppant

Vincent

¹

,

Miller

²

,

Milton-Tayler³

et al. 2004

SPE Annual Technical Conference and Exhibition

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDuring fracture stimulation treatments, particle-laden slurries may damage pumping equipment and have been shown to erode perforation tunnels. During subsequent flowback operations, minor to severe erosion of surface equipment may be observed if formation sand and/or proppants are produced. This paper compares the erosivity of sand-based and ceramic proppants. This paper will examine the erosion mechanisms and demonstrate that theoretical and laboratory measurements are in agreement that low density ceramic proppants, due to the superior roundness and sphericity, are less erosive than more angular sand products.Real-world results from the oilfield, the waterjet industry, pump and valve manufacturers, and the abrasive industry will be reviewed to substantiate the conclusion that proppant angularity is a dominant parameter that increases erosion in typical pumping and flowback conditions. Impingement tests designed to simulate flowback conditions demonstrate that s ubstituting a spherical lightweight ceramic may reduce wellhead or other impingement surface erosion by up to 95% compared to an angular sand. The highest quality frac sand was nine times more erosive than lightweight ceramic (LWC) in impingement studies. Additional studies utilizing intentionally crushed proppant to increase angularity demonstrate that proppant shape is a dominant factor which controls erosion. Surprisingly, flowback testing has shown that resin coatings applied to proppant have the potential to increase erosion by 15-fold. The authors believe this is partially due to a focusing effect attributed to electrostatic charge. Test alterations with multiphase flow have reduced, but not eliminated, this effect.Slurry abrasion testing has shown that the highest quality frac sands are over 250% as abrasive as LWC. Although frac sands are often specified to withstand several thousand pounds of closure stress, significant sand degradation was observed after exposure to a reciprocating five pound weight. Erosivity and abrasivity of all proppant types were shown to increase with proppant damage. Erosion within chokes was found to be three times higher with sand than with lightweight ceramic.Despite conventional wisdom to the contrary, a number of recent laboratory studies have demonstrated that spherical proppants are less likely to flow back from the fracture as compared to more angular products. All data indicate that equipment erosion occurring during the stimulation treatment and subsequent flowback can be substantially reduced through the use of spherical lightweight ceramic proppants.

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Experimental Investigation of Proppant Flowback Phenomena Using a Large Scale Fracturing Simulator

Cited by 4 publications

References 14 publications

Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

Erosion by Proppant: A Comparison of the Erosivity of Sand and Ceramic Proppants During Slurry Injection and Flowback of Proppant

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