Shale Acid Fracturing: Geomechanical Effects and Fracture Propagation

Shovkun, Igor; Espinoza, D. Nicolas

doi:10.1061/9780784480779.238

Cited by 5 publications

(9 citation statements)

References 5 publications

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“…Many faults are already close to a state of critical equilibrium between formation fluid pressures and in situ stresses, in which small perturbations can induce fault slip . Mineral dissolution in the reservoir rock can promote horizontal stress relaxation, and stress transfer to adjacent faults …”

Section: Discussionmentioning

confidence: 99%

“…49,50 Mineral dissolution in the reservoir rock can promote horizontal stress relaxation, and stress transfer to adjacent faults. 21,22 Despite some drawbacks from mineral dissolution, CO 2 -induced rock alteration may exhibit self-healing mechanisms. Mineral precipitation from exsolution along fault leakage paths has shown to reduce porosity, and therefore permeability, in the rock matrix (Entrada Sandstone fault gouge rock and Salt Wash Sandstonealso at Crystal Geyser) and in fractures.…”

Section: Large-scale Implicationsmentioning

confidence: 99%

“…The potential effect of the reacted ‘skin’ on the bulk strength of the core would be limited, rendering traditional rock mechanics tests, such as unconfined compressive strength testing, triaxial testing and elastic wave velocity measurement, ineffective. Micromechanics tests such as the indentation test and the scratch test offer a practical alternative by preferentially probing the reacted region …”

Section: Introductionmentioning

confidence: 99%

“…[15][16][17][18][19] Changes in mechanical properties can trigger strains and stress changes within and around the altered rock with undesirable implications for caprock integrity and well-casing integrity. Mineral dissolution imparts changes similar to those induced by reservoir cooling or depletion 20,21 with the extent of alterations depending on rock fabric, and the availability of reactive mineral phases and CO 2 . Laboratory experiments and coupled chemo-mechanical models show that mineral dissolution can result in a decrease in horizontal effective stress, potentially resulting in either compaction-driven shear failure or stress intensification in the caprock.…”

Section: Introductionmentioning

confidence: 99%

“…Micromechanics tests such as the indentation test and the scratch test offer a practical alternative by preferentially probing the reacted region. [13][14][15][16][17][18][19][20][21][22][23][24] Laboratory derived dissolution rate equations, rate constants, and activation energies from batch experiments with minerals and rocks can be used to describe the dissolution for a given mineral in a distinct rock type, but the laboratory-derived mineral dissolution rates can be orders of magnitude faster than those observed in the field. 12 Experiments using mineral powders are useful as a first step toward investigation of mineral reaction mechanisms and kinetics, while giving the advantage of shorter run times.…”

Section: Introductionmentioning

confidence: 99%

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CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

et al. 2017

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The injection of carbon dioxide (CO2) into geological formations results in a chemical re‐equilibration between the mineral assemblage and the pore fluid, with ensuing mineral dissolution and re‐precipitation. Hence, target rock formations may exhibit changes of mechanical and petrophysical properties due to CO2 exposure. We conducted batch reaction experiments with Entrada Sandstone and Summerville Siltstone exposed to de‐ionized water and synthetic brine under reservoir pressure (9–10 MPa) and temperature (80°C) for up to four weeks. Samples originate from the Crystal Geyser field site, where a naturally occurring CO2 seepage alters portions of these geologic formations. We conducted micro‐scratch tests on rock samples without alteration, altered under laboratory conditions, and naturally altered over geologic time. Scratch toughness and hardness decrease as a function of exposure time and water salinity up to 52% in the case of Entrada and 87% in the case of Summerville after CO2‐induced alteration in the laboratory. Imaging of altered cores with SEM‐EDS and X‐ray microCT methods show dissolution of carbonate and silica cements and matrix accompanied by minor dissolution of Fe‐oxides, clays, and other silicates. Parallel experiments using powdered samples confirm that dissolution of carbonate and silica are the primary reactions. The batch reaction experiments in the autoclave utilize a high fluid to rock volume ratio and represent an end member of possible alteration associated with CO2 storage systems. These types of tests serve as a pre‐screening tool to identify the susceptibility of rock facies to CO2‐related chemical‐mechanical alteration during long‐term CO2 storage. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 99%

Section: Large-scale Implicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

et al. 2017

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Effect of polyacrylamide friction reducer on calcite dissolution rate at 25 °C and implication for hydraulic fracturing

Walkinshaw

Belshaw

et al. 2021

Journal of Natural Gas Science and Engineering

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Hydraulic fracturing is widely used to create cracks and increase the size and connectivity of existing fractures, leading to higher permeability of shale rocks and production of unconventional hydrocarbon sources. The main chemicals used in hydraulic fracturing fluids can initiate fractures in shale reservoirs by acid induced carbonate dissolution, and minimise energy loss during the pumping process by friction reducer enhanced fluid viscosity. Here, using batch reactor experiments we investigate the effect of non-ionic polyacrylamide polymer (friction reducer) on the dissolution rate of calcite in acidic solutions (0.2 M buffer solution of sodium acetate/acetic acid) at 25 °C. The results demonstrate that polyacrylamide (from 0 to 30 mg) slows down the dissolution rate by a factor of 4. Hydrogen bonding and surface complexation between non-ionic polyacrylamide and calcite potentially trigger an adsorption mechanism that protects calcite from dissolving.This research provides new insights into friction reducer (polyacrylamide) influenced pore generation, enabling engineers to optimise the fracturing fluid design (amount of polyacrylamide) and to consider suitable actions to prevent the polymer from having a negative impact on productivity.

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A Critical Review of the Physicochemical Impacts of Water Chemistry on Shale in Hydraulic Fracturing Systems

Khan

Spielman-Sun

Jew

et al. 2021

Environ. Sci. Technol.

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Hydraulic fracturing of unconventional hydrocarbon resources involves the sequential injection of a high-pressure, particle-laden fluid with varying pH’s to make commercial production viable in low permeability rocks. This process both requires and produces extraordinary volumes of water. The water used for hydraulic fracturing is typically fresh, whereas “flowback” water is typically saline with a variety of additives which complicate safe disposal. As production operations continue to expand, there is an increasing interest in treating and reusing this high-salinity produced water for further fracturing. Here we review the relevant transport and geochemical properties of shales, and critically analyze the impact of water chemistry (including produced water) on these properties. We discuss five major geochemical mechanisms that are prominently involved in the temporal and spatial evolution of fractures during the stimulation and production phase: shale softening, mineral dissolution, mineral precipitation, fines migration, and wettability alteration. A higher salinity fluid creates both benefits and complications in controlling these mechanisms. For example, higher salinity fluid inhibits clay dispersion, but simultaneously requires more additives to achieve appropriate viscosity for proppant emplacement. In total this review highlights the nuances of enhanced hydrogeochemical shale stimulation in relation to the choice of fracturing fluid chemistry.

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Shale Acid Fracturing: Geomechanical Effects and Fracture Propagation

Cited by 5 publications

References 5 publications

CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

Effect of polyacrylamide friction reducer on calcite dissolution rate at 25 °C and implication for hydraulic fracturing

A Critical Review of the Physicochemical Impacts of Water Chemistry on Shale in Hydraulic Fracturing Systems

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Shale Acid Fracturing: Geomechanical Effects and Fracture Propagation

Cited by 5 publications

References 5 publications

CO2‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

CO2‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

Effect of polyacrylamide friction reducer on calcite dissolution rate at 25 °C and implication for hydraulic fracturing

A Critical Review of the Physicochemical Impacts of Water Chemistry on Shale in Hydraulic Fracturing Systems

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CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

CO₂‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing