Abstract:Shale rocks are an integral part of petroleum systems. Though, originally viewed primarily as source and seal rocks, introduction of horizontal drilling and hydraulic fracturing technologies have essentially redefined the role of shale rocks in unconventional reservoirs. In the geological setting, the deposition, formation and transformation of sedimentary rocks are characterised by interactions between their clay components and formation fluids at subsurface elevated temperatures and pressures. The main drivi… Show more
“…The Caney Shale is a largely unexploited but potentially economically viable unconventional petroleum formation found within the South-Central Oklahoma Oil Province (SCOOP). − This formation was regarded a source and seal formation, accounting for its present relatively unexploited status. ,,, The target for drilling in the area in the past has been the Woodford Shale, which directly underlies the Caney Shale. Though the Caney Shale is replete with recoverable hydrocarbon resources, research and exploration activity undertaken on this formation is limited.…”
Interactions between rock minerals and hydraulic fracturing
fluids
directly impact the geochemical and geomechanical properties of shale
formations. However, the mechanisms of geochemical reactions in shale
unconventional reservoirs remain poorly understood. To investigate
the geochemical reactions between shale and hydraulic fracturing fluids,
a series of batch reactor experiments were undertaken. Three rock
samples with different mineralogical compositions and three fluid
samples of different compositions [deionized water, deionized water
+ 2% potassium chloride (KCl), and deionized water + 0.5% choline
chloride (C5H14ClNO)] were used. Experiments
were undertaken at reservoir temperature and atmospheric pressure.
Elemental compositions of effluents after 1, 3, 7, 14, and 28 days
were analyzed using inductively coupled plasma mass spectrometry.
Medical computed tomography scanning and X-ray fluorescence spectroscopy
were conducted on the entire core to help upscale results obtained
from rock–fluid interaction experiments. Geochemical modeling
using a reactive simulator, TOUGHREACT, was undertaken to corroborate
experimental results. Results show that a lower pH triggered high
dissolution rates in the rock samples, especially the carbonate components.
As the pH increased, the rate of dissolution declined significantly,
though for most cases dissolution still continued. The observed dissolved
silica concentrations were much higher than the quartz solubility,
suggesting that much of the silica originated from more soluble silica
polymorphs and possibly desorption from clay mineral exchange sites.
The concentration of most elemental species in solution increased,
but aluminum (Al) and magnesium (Mg) concentrations declined rapidly
following initial entry into solution. Geochemical modeling corroborated
the conclusions regarding mineral dissolution and precipitation observed
from experiments, notably the dissolution of calcite and pyrite in
the reacted shale samples, the likely presence of silica polymorphs
such as opal, chalcedony, or amorphous silica in these samples, and
the reduction of Al and Mg concentrations in solution by precipitation
of secondary aluminosilicate phases. The de-flocculation of clay minerals
during reaction implies fines migration after hydraulic fracturing.
This is detrimental to reservoir productivity as clay fines are displaced
and lodged within the micro- and nanofractures created during fracturing.
The immediate consumption of Al and Mg also has implications on blockage
of hydrocarbon pathways due to precipitation of new minerals in these
locations.
“…The Caney Shale is a largely unexploited but potentially economically viable unconventional petroleum formation found within the South-Central Oklahoma Oil Province (SCOOP). − This formation was regarded a source and seal formation, accounting for its present relatively unexploited status. ,,, The target for drilling in the area in the past has been the Woodford Shale, which directly underlies the Caney Shale. Though the Caney Shale is replete with recoverable hydrocarbon resources, research and exploration activity undertaken on this formation is limited.…”
Interactions between rock minerals and hydraulic fracturing
fluids
directly impact the geochemical and geomechanical properties of shale
formations. However, the mechanisms of geochemical reactions in shale
unconventional reservoirs remain poorly understood. To investigate
the geochemical reactions between shale and hydraulic fracturing fluids,
a series of batch reactor experiments were undertaken. Three rock
samples with different mineralogical compositions and three fluid
samples of different compositions [deionized water, deionized water
+ 2% potassium chloride (KCl), and deionized water + 0.5% choline
chloride (C5H14ClNO)] were used. Experiments
were undertaken at reservoir temperature and atmospheric pressure.
Elemental compositions of effluents after 1, 3, 7, 14, and 28 days
were analyzed using inductively coupled plasma mass spectrometry.
Medical computed tomography scanning and X-ray fluorescence spectroscopy
were conducted on the entire core to help upscale results obtained
from rock–fluid interaction experiments. Geochemical modeling
using a reactive simulator, TOUGHREACT, was undertaken to corroborate
experimental results. Results show that a lower pH triggered high
dissolution rates in the rock samples, especially the carbonate components.
As the pH increased, the rate of dissolution declined significantly,
though for most cases dissolution still continued. The observed dissolved
silica concentrations were much higher than the quartz solubility,
suggesting that much of the silica originated from more soluble silica
polymorphs and possibly desorption from clay mineral exchange sites.
The concentration of most elemental species in solution increased,
but aluminum (Al) and magnesium (Mg) concentrations declined rapidly
following initial entry into solution. Geochemical modeling corroborated
the conclusions regarding mineral dissolution and precipitation observed
from experiments, notably the dissolution of calcite and pyrite in
the reacted shale samples, the likely presence of silica polymorphs
such as opal, chalcedony, or amorphous silica in these samples, and
the reduction of Al and Mg concentrations in solution by precipitation
of secondary aluminosilicate phases. The de-flocculation of clay minerals
during reaction implies fines migration after hydraulic fracturing.
This is detrimental to reservoir productivity as clay fines are displaced
and lodged within the micro- and nanofractures created during fracturing.
The immediate consumption of Al and Mg also has implications on blockage
of hydrocarbon pathways due to precipitation of new minerals in these
locations.
“…The dissolution of Mn can lead to the formation of amorphous hydrous silica and alumina, which can potentially clog pores within the matrix and fractures, leading to a reduction in permeability [37]. The safe limit for Mn in drinking water is 0.05 ppm, which is exceeded in all samples (average DI water: 4.10 ppm, FF: 4.85 ppm) [36,38]. The presence of high levels of Mn in the effluents could potentially have adverse effects on human health and the environment.…”
Section: The Minor Elements Foundmentioning
confidence: 99%
“…Cobalt can occur in shale formations as a component of clay minerals such as illite and smectite. The dissolution of Co could lead to the formation of amorphous hydrous silica and alumina, which could potentially clog pores within the matrix and fractures, leading to a reduction in permeability [38]. Cobalt is not considered to be a major environmental or health concern, and there is no established safe limit for Co in drinking water [39].…”
The Marcellus shale is an unconventional reservoir of significant economic potential with Total Organic Carbon (TOC) ranging from 1 to 20%. Hydraulic fracturing is used to extract the shale’s resources, which requires large amounts of water and can result in mineral-rich flowback waters containing hazardous contaminants. This study focuses on a geochemical analysis of the flowback waters and an evaluation of the potential environmental impacts on water and soil quality. Drilled core samples from different depths were treated with lab-prepared hydraulic fracturing fluids. Rock samples were analyzed using Energy Dispersive Spectroscopy (EDS), while effluents’ chemical compositions were obtained using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). A comparison of results from drilled core samples treated with additives for hydraulic fracturing to those treated with deionized (DI) water confirms that, as expected, the major elements present in the effluent were Ca, Ba, and Cl in concentrations greater than 100 µg/L. The most concerning elements in the effluent samples include As, Ca, Cd, Pb, Se, S, K, Na, B, Mo, and Mn, with Cd and Cr values averaging 380 and 320 µg/L, respectively, which are above safe limits. Se concentrations and high levels of Ca pose major safety and scaling concerns, respectively. We also compared Marcellus shale drilled core samples’ geochemical reactivity to samples collected from an outcrop.
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