Abstract
Ceramic proppants are determined as material designed for hydraulic fracturing in the shale gas industry. Shale formation is fractured due to pumping the fracturing fluid including proppants into the unconventional well. Ceramic granulates set in the newly created fissures act as a prop and permit the shale gas of flowing up the well. The aim of this research was to study and compare ceramic materials used as proppants. The investigation includes four kinds of industrial proppants in green state obtained in a way of mechanical granulation process without binder and with poly(acrylic–styrene) dispersion in amount of 5 mass% with respect to the powder. Green pellets and afterward sintered granulates with 16/20 and 20/40 mesh were also analyzed and compared. Usefulness of green pellets was estimated basing on bulk density, thermal analysis, thermogravimetry, roundness coefficient and porosity results. Structure, morphology and chemical composition of the green state samples were determined by scanning electron microscopy with energy-dispersive spectroscopy. The sintered proppants were also characterized with X-ray tomography, turbidity and solubility in acid. Mechanical strength of these samples was established during subjection to crush test. The outcomes show a suitability of the studied material and prove chemical composition and grain size influence on the integrity of created fractures and therefore the extraction of the unconventional gas out of the well.
Highlights
Natural gas is one of the most important sources of energy on the global market that reduces CO2 emissions more than twice in case of coal and 40 % lower than oil
It is predicted that global shale gas extraction will increase from 13 % in 2009 up to 23 % in 2035 which is equal to 1.6 bln m3 [3]
X-ray diffraction (XRD) analysis of raw materials used for the proppants production indicated dominating presence of boehmite and kaolinite, and in minor amounts phases of calcite, anatase, rutile and hematite
Summary
Natural gas is one of the most important sources of energy on the global market that reduces CO2 emissions more than twice in case of coal and 40 % lower than oil. A real and promising perspective for replacing conventional resources can be deposits of unconventional natural gas that occurs in shale [1]. This group of hydrocarbons, formed by resources trapped in impervious rocks, demands specific fracturing ways. Standard permeability of conventional deposits totals up 10−3 D (Darcy), while it is much lower on the scale for the shale gas (10−9 D) [2]. Scale of European unconventional reservoirs is thrice smaller (Sweden (1.2 bln m3), Ukraine (1.2 bln m3), France (5.1 bln m3), UK (5 bln m3), Norway (2.4 bln m3), Germany (7–22 bln m3) and Poland (0.8 bln m3)) where deposits occur twice deeper (up to 6 km) in comparison with US shales. Polish shale formations consist of quartz, loamy, silica, marly and bituminous rocks that determine more severe geological and geochemical parameters than American ones [4]
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