Laboratory Investigation of Proppant-Pack Conductivity: Eagle Ford and Vaca Muerta Shale
- Abhinav Mittal (University of Oklahoma) | Chandra S. Rai (University of Oklahoma) | Carl H. Sondergeld (University of Oklahoma)
- Document ID
- Unconventional Resources Technology Conference
- SPE/AAPG/SEG Unconventional Resources Technology Conference, 24-26 July, Austin, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. Unconventional Resources Technology Conference
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- 249 since 2007
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Hydraulic fractures act as conduits connecting a wellbore to nanodarcy permeability unconventional reservoirs. Proppants are responsible for enhancing the fracture conductivity and help in maintaining high production rates. This study is focused on the measurement of long-term conductivity of proppant-packs at simulated reservoir temperature and pressure conditions. Various conductivity impairment mechanisms such as proppant crushing, fines migration, embedment, and diagenesis are investigated.
Testing was done using a conductivity cell which allows simultaneous measurement of fracture compaction and permeability. The proppant-pack performance during compression between metal and shale platens was compared. The proppant filled fracture (concentration: 0.75-3 lb/ft2) is subjected to axial load (5000 psi) to simulate closure stress. Brine (3% NaCl + 0.5% KCl) is flowed through the pack at a constant rate (3 ml/min) at 250°F over an extended duration of time (10-60 days). In this study, Ottawa sand proppant was used between platen faces fabricated from Vaca Muerta and Eagle Ford shales.
Testing between metal platens indicated the reduction in permeability with 20/40 mesh Ottawa sand (~30% over 12 days) was less than that of 60/100 mesh Ottawa sand which suffered a 99% reduction in only 4 days.
Measurements with 20/40 mesh Ottawa sand between shale platens were conducted at 1.5 lb/ ft2. Over a duration of 10 days, the Eagle Ford platens proppant-pack exhibits a greater reduction in permeability, in comparison to Vaca Muerta platens. The normalized compaction for Eagle Ford shale platens is 20% more than Vaca Muerta platens, owing to greater proppant embedment. Particle size analysis and SEM images verify proppant crushing, fines migration and embedment as dominant damage mechanisms. These factors are observed to be dependent on the shales being tested. The results suggest a substantial degradation of permeability during the initial 5 days of testing, after which the permeability appears to stabilize. Crushed proppant and dislodged shale surface particles contribute to the fines generated; a greater concentration of fines is observed downstream. For tests between Vaca Muerta platens under similar pressure and temperature conditions and 2lb/ ft2 proppant concentration, over 60 days, the permeability reduced by almost three orders of magnitude. It was also observed that growth of digenetic smectite is accelerated by making the fluid more basic (pH: 10).
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