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Determining osmotic pressure in Niobrara chalk and Codell sandstone using high-speed centrifuge
Uzun, Ilker Ozan
Uzun, Ilker Ozan
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2018
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2020-01-02
Abstract
Low salinity waterflooding is an emerging enhanced oil recovery (EOR) technique that has attracted the attention of the oil industry. However, the classical application of waterflooding in unconventional shale reservoirs is impractical because of the nanoscale dimension of the matrix pores. Salinity contrast across shale matrix blocks leads to osmotic pressures which expels oil from tight shale. This thesis exploited this phenomenon to measure osmotic pressure in shale core plugs. Typically, all the unconventional shale reservoirs produce hydrocarbon after hydraulic fracture stimulation. The stimulation treatment is performed using slick water and some gel components. A large percentage of this injected fluid is trapped inside the pores and cannot be produced. The findings and results of this thesis can be used to investigate the osmotic effect of the hydraulic fracturing fluids in tight shale formations. This thesis includes measurement of osmotic pressure using ultra-high-speed centrifuge experiments and calculation of membrane efficiency for unconventional Niobrara chalk and Codell sandstone formations. The laboratory experiments show that the low-salinity brine is imbibed into the core samples in greater quantities compared to that of high-salinity brine. The brine imbibition is measured by displacement and production of resident oil in the core. Measured membrane efficiency of Niobrara B-Chalk, with permeability of 0.0022-0.0099 md, is 75 % of perfect membrane. Accounting for chalk solubility in brine within the pores should reduce the membrane efficiency to about 50%. Similarly, measured membrane efficiency of Codell sandstone, with permeability of 0.0085-0.0105 md, is 2.4 % of the perfect membrane.
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