Gas-driven subcritical crack propagation during the conversion of oil to gas

Fan, Zhihua; Jin, Z.-H.; Johnson, Scott E.

doi:10.1144/1354-079311-030

Cited by 21 publications

(16 citation statements)

References 30 publications

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“…Such slow crack propagation, also called subcritical crack growth, is responsible for brittle creep in rocks [Brantut et al, 2013[Brantut et al, , 2014Rutter, 1976;Croizé et al, 2010]. Understanding the role of subcritical cracking in rock deformation is also relevant for prospecting and exploitation of hydrocarbons [Fan et al, 2012] and geothermal resources [Ghassemi, 2012], and for the long-term stability of geological reservoirs where CO 2 could be permanently stored [Rohmer et al, 2014]. Finally, microfractures that develop in rocks through subcritical crack growth modify the elastic, strength, and fluid transport properties of these rocks [Anders et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

et al. 2016

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Chemically activated processes of subcritical cracking in calcite control the time‐dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5–7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in calcite single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10−9–10−2 m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for calcite saturated solutions, the energy necessary to fracture calcite is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in calcite than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5–7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of calcite. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.

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Section: Introductionmentioning

confidence: 99%

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

et al. 2016

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“…Fracture extension also occurs from the tensile and not the compressive stress concentrations under both tensile and compressive loading. Fan et al (2012) stated that microcracks induced by the excess oil/gas pressure may propagate and form an interconnected fracture network. This indicates also that during production, different pressure regimes could change characteristics of fractures.…”

Section: Fracture Simulation Methods For Carbonate Rocksmentioning

confidence: 99%

“…It also might create fractures which make connections between vugs, while cracks could be widened and/or become fractures. Fan et al (2012) investigated mechanism of fracture propagation by a linear elastic model. They have shown that critical crack propagation takes place if the intensity of the induced stress reaches the fracture toughness of the reservoir rock.…”

Section: Fracture Simulation Methods For Carbonate Rocksmentioning

confidence: 99%

Naturally fractured hydrocarbon reservoir simulation by elastic fracture modeling

Soleimani

2017

Pet. Sci.

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Accurate fluid flow simulation in geologically complex reservoirs is of particular importance in construction of reservoir simulators. General approaches in naturally fractured reservoir simulation involve use of unstructured grids or a structured grid coupled with locally unstructured grids and discrete fracture models. These methods suffer from drawbacks such as lack of flexibility and of ease of updating. In this study, I combined fracture modeling by elastic gridding which improves flexibility, especially in complex reservoirs. The proposed model revises conventional modeling fractures by hard rigid planes that do not change through production. This is a dubious assumption, especially in reservoirs with a high production rate in the beginning. The proposed elastic fracture modeling considers changes in fracture properties, shape and aperture through the simulation. This strategy is only reliable for naturally fractured reservoirs with high fracture permeability and less permeable matrix and parallel fractures with less cross-connections. Comparison of elastic fracture modeling results with conventional modeling showed that these assumptions will cause production pressure to enlarge fracture apertures and change fracture shapes, which consequently results in lower production compared with what was previously assumed. It is concluded that an elastic gridded model could better simulate reservoir performance.

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“…Changes of pore pressure can result simply from burial and uplift processes during basin subsidence. In hydrocarbon reservoirs, pore pressure is commonly increased by oil and gas generation (see, for example, introductory discussion of Fan et al 2012).…”

Section: Summary Of the Numerical Testsmentioning

confidence: 99%

Effective stress history and the potential for seismicity associated with hydraulic fracturing of shale reservoirs

Harper

2014

JGS

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The influence of effective stress history on reservoir stability and the response to hydraulic fracturing are simulated for two hypothetical shale reservoirs. It is numerically demonstrated that the effective stress history influences the present-day stability of faults and natural fractures. Any assumption of a homogeneous stress state is shown to be unrealistic in the majority of fractured shale reservoirs. The simulations demonstrate that, depending upon the effective stress history, shear displacements can be induced by stress changes associated with stimulation without a change of fluid pressure in the destabilized fractures. Elastoplastic shale and other fractured reservoirs are shown to have a memory of past geomechanical states. These numerical findings demonstrate the value of interpreting reservoir effective stress history when planning fluid injection. A previous case history is summarized to illustrate the overwhelming dependence of stress history analyses on a wide spectrum of earth science disciplines. It also illustrates the application of stress history analyses to activities other than hydraulic fracturing. The current inexperience of effective stress history description means that new approaches must be identified to optimize the necessary multidisciplinary investigations.

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Gas-driven subcritical crack propagation during the conversion of oil to gas

Cited by 21 publications

References 30 publications

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

Naturally fractured hydrocarbon reservoir simulation by elastic fracture modeling

Effective stress history and the potential for seismicity associated with hydraulic fracturing of shale reservoirs

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