Chapter 2 Origin of abnormal formation pressures

Chilingar, George V.; Robertson, John O.; Rieke, Herman H.

doi:10.1016/s0376-7361(02)80023-1

Cited by 13 publications

(16 citation statements)

References 28 publications

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“…Excess pressure can be generated by several mechanisms. For example, artesian aquifers and petroleum reservoirs may be highly pressured due to impermeable seals and the buoyancy of the fluids (de Marsily, 1986;Chilingar et al, 2002;Deming, 2002).…”

Section: Hydrofracture Emplacement Hydrofracture Initiationmentioning

confidence: 99%

“…Fluid overpressure, as defined here, is not to be confused with an abnormal pore formation pressure. Such confusion may occur because in part of the literature the hydrostatic pressure is regarded as normal, a lower formation pressure is referred to as subnormal, and a higher formation pressure as supernormal (Selley, 1998) or overpressure (Hubbert and Rubey, 1959;Chapman, 1981;Dahlberg, 1994;Chilingar et al, 2002).…”

Section: Fluid Overpressure Of Hydrofracturesmentioning

confidence: 99%

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Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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Fractures generated by internal fluid pressure, for example, dykes, mineral veins, many joints and man-made hydraulic fractures, are referred to as hydrofractures. Together with shear fractures, they contribute significantly to the permeability of fluid reservoirs such as those of petroleum, geothermal water, and groundwater. Analytical and numerical models show that-in homogeneous host rocks-any significant overpressure in hydrofractures theoretically generates very high crack tip tensile stresses. Consequently, overpressured hydrofractures should propagate and help to form interconnected fracture systems that would then contribute to the permeability of fluid reservoirs. Field observations, however, show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts and do not form vertically interconnected networks. The most important factors that contribute to hydrofracture arrest are discontinuities (including contacts), stiffness changes between layers, and stress barriers, where the local stress field is unfavorable to hydrofracture propagation. A necessary condition for a hydrofracture to propagate to the surface is that the stress field along its potential path is everywhere favorable to extension-fracture formation so that the probability of hydrofracture arrest is minimized. Mechanical layering and the resulting heterogeneous stress field largely control whether evolving hydrofractures become confined to single layers (stratabound fractures) or not (non-stratabound fractures) and, therefore, if a vertically interconnected fracture system forms. Non-stratabound hydrofractures may propagate through many layers and generate interconnected fracture systems. Such systems commonly reach the percolation threshold and largely control the overall permeability of the fluid reservoirs within which they develop.

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Section: Hydrofracture Emplacement Hydrofracture Initiationmentioning

confidence: 99%

Section: Fluid Overpressure Of Hydrofracturesmentioning

confidence: 99%

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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“…Abnormal fluid pressures occur in low-permeability formations where the ability to gain or drain water is less than changes that have occurred in the fluid or pore volumes. The causes of this phenomenon might be physical, chemical or both (Chilingar et al 2002) and they may be unique for every sedimentary basin (Matusevich et al 1997). Defining the causes of abnormal pressure and its progress with time is important in defining groundwater movement and solute transport over a long time scale especially for nuclear waste disposal.…”

Section: Introductionmentioning

confidence: 99%

Impacts of Pleistocene glacial loading on abnormal pore‐water pressure in the eastern Michigan Basin

Khader

Novakowski

2014

Geofluids

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The hydromechanical effects of Pleistocene glacial loading on the Michigan Basin are assessed using numerical analysis based on coupled stress and pore-water pressure. The two-dimensional model domain included the Basin cross section and extended 10 km into the Precambrian. In the analysis, we considered the effects of the number of glacial loading cycles, the presence and connectedness of a deep Cambrian aquifer, the direction of glacial advance, the effect of a wet versus dry glacier/soil interface, topographic effects, density-driven flow effects, and lithosphere flexure on the development of anomalous pressures. The modeling results were compared with data collected from highly instrumented wells completed in the eastern margin of the Basin. The present-day results define regions of significant underpressure in the upper Ordovician and lower Silurian formations characterized by very low hydraulic conductivity and regions of overpressure where hydraulic conductivity is higher. To achieve the degree of underpressure observed in the instrumented wells using the model, a specific loading cycle applied over 100 000 years was repeated four times. As the number of loading cycles increased, the Paleozoic formations reached a state where the underpressures remain constant. Our results also illustrate the difference in poroelastic modeling between the application of mechanical loads on the land surface and the application of an equivalent hydraulic head, where the latter developed overpressures rather than the observed underpressures. The modeling also shows that the overpressures observed in the Cambrian formations are most likely to be the result of density-driven flow. Finally, the simulations show that the effects of lithosphere flexure in the hydromechanical models results in the development of lateral stresses that generate overpressures rather than underpressures in the southern half of the domain. As there are no suitable observation points, these results remain unconfirmed, and further study is warranted.

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“…Abnormal fluid pressures, which can be defined as a variation in fluid pressure relative to hydrostatic pressure, are frequently encountered in subsurface environments, at a wide range of depths and geological settings [ Chilingar et al , 2002]. Interpretation of the origin of abnormal pressures enables information to be obtained on the hydrodynamics in the studied formation [ Neuzil , 1995].…”

Section: Introductionmentioning

confidence: 99%

Natural conditions for more limited osmotic abnormal fluid pressures in sedimentary basins

Trémosa

Gonçalvès

Matray

2012

Water Resources Research

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[1] Chemical osmosis is considered a plausible cause of abnormal pressures in shale formations of sedimentary basins. A set of experimental data on chemical osmosis was recently obtained for different shales, mainly in the framework of studies on radioactive waste repositories in deep argillaceous formations. Based on these data, large, osmotically induced overpressures up to tens of MPa were predicted by Neuzil and Provost [2009] under appropriate conditions. However, such large overpressures have not been found in sedimentary basins such that the reasons for this disparity between predictions and observations need to be clarified. Accordingly, two natural causes for lower than expected osmotic pressure were investigated: the effect of the complex composition of natural waters, including both monovalent and divalent cations, on the osmotic efficiency and the resulting abnormal pressures, and the presence of steady state rather than transient-state salinity distributions. For this purpose, an electrical triple-layer model accounting for multi-ionic solutions was developed and used to calculate the osmotic efficiency at different proportions of monovalent and divalent cations. The calculated decrease of the osmotic efficiency when Ca 2þ is introduced in a Na þ -clay system yields a noticeable decrease in the ability of the shale to generate overpressures. A discussion addresses the generation of abnormal pressures at steady state conditions found in sedimentary basins, i.e., with a linear distribution of the concentration across the formation. The persistence of moderate overpressures was predicted because of the nonlinearity associated with the dependence of the chemo-osmotic efficiency on the concentration and the porosity. Finally, a case study of the moderate excess hydraulic head measured in the Toarcian/Domerian argillaceous formation of Tournemire (SE of France) was investigated. The analysis indicated an osmotic origin for the excess head and illustrated the influence of the pore water composition.

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Chapter 2 Origin of abnormal formation pressures

Cited by 13 publications

References 28 publications

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Impacts of Pleistocene glacial loading on abnormal pore‐water pressure in the eastern Michigan Basin

Natural conditions for more limited osmotic abnormal fluid pressures in sedimentary basins

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