Pore fluid pressure

A series of processes will control the behaviour of C02 in saline aquifer formations. First, the C02 will displace the formation water (brine) originally in place and will lead to a local increase in pore fluid pressure (van der Meer, 1992). The injected C02 will not be distributed evenly, but will finger out, owing to the lower density than the pore waters and the heterogeneities of the aquifer. Doughty et al. (2001) point out that the shape of the C02 plume in the aquifer will be highly site- and case-specific. Carbon dioxide will rise to the top of the aquifer and migrate at the bottom of the... 

Soft biological structures exhibit finite strains and nonlinear anisotropic material response. The hydrated tissue can be viewed as a fluid-saturated porous medium or a continuum mixture of incompressible solid (s), mobile incompressible fluid (f), and three (or an arbitrary number) mobile charged species a, (3 = p,m, b). A mixed Electro-Mechano-Chemical-Porous-Media-Transport or EMCPMT theory (previously denoted as the LMPHETS theory) is presented with (a) primary fields (continuous at material interfaces) displacements, Ui and generalized potentials, ifi ( , r/ = /, e, to, b) and (b) secondary fields (discontinuous) pore fluid pressure, pf electrical potential, /7e and species concentration (molarity), ca = dna/dVf or apparent concentration, ca = nca and c = Jnca = dna/dVo. The porosity, n = 1 — J-1(l — no) and no = no(Xi) = dVj/dVo for a fluid-saturated solid. Fixed charge density (FCD) in the solid is defined as cF = dnF/dV , cF = ncF, and cF = cF (Xf = JncF = dnF/d o. 

Figure 8.26. Pressure and temperature variations in the burial diagenetic realm. A. Static pressure variations most pore fluid pressures plot in the stippled area. B. Depth-temperature plots assuming different geothermal gradients gradients in the shallow crust are generally in the range of 20° to 30° km-1. (After Choquette and James, 1987.)...

Makarov, V.K. and L.J. Morozov, 1980. Hydrodynamic barriers in petroliferous basins of North Africa. International Geology Review, Vol. 22, no. 11, pp. 1286-1290 Mann, D.M. and A.S. Mackenzie, 1990. Prediction of pore fluid pressures in sedimentary basins. Marine and Petroleum Geology, 7, pp. 55-65 Mann, U., 1989. Revealing hydrocarbon migration pathways. Geologische Rundschau 78/1, pp. 337-348... 

Smith, J.E., 1971. The dynamics of shale compaction and evolution of pore-fluid pressures. 

Abnormal pore fluid pressures are known to occur worldwide. By definition these pressures are either higher or lower than the hydrostatic pressure, which is the pressure required to support a column of fluid from subsurface formation to the surface. In this paper, the word geopressure is used to denote those pore pressures which are higher than the hydrostatic pressure. 

According to the Terzaghi principle, the effect of pore fluid pressure (P) and total stress (5) on tensile failure can be described by the Terzaghi effective stress o (Hubbert and Rubey, 1959), given by... 

Subsurface tension fractures will form when the minimum effective stress (CTj) reduces to the tensile strength of the rock (-C,). This will occur when the minimum total stress (S3) is reduced by tectonic dilation, or pore fluid pressure is increased (Watts, 1987). These failure conditions can be summarised as follows ... 

Hydraulic breaching occurs when pore fluid pressure exceeds the total minimum confining stress and the tensile strength of the rock (Eq. (3)). In order to understand how this process works, the difference between pore-pressure build-up within the cap-rocks and underlying reservoir needs to be clarified. 

As indicated by Eq. (3), in order to breach the seal, underlying reservoir pore fluid pressure (Preservoir) must exceed the horizontal total stress (S3) plus the rock strength of the seal (Cj). By combining Eqs. (3) and (7), it can be shown that the condition required for seal breaching by underlying reservoir pressure is as follows ... 

The mass transfer problem may be resolved if eogenetic pore fluids were transmitted locally across the GGF in response to fault-related changes in pore pressure and near-surface hydrology (e.g. Knipe, 1993). The cemented fractures at Ballycastle show clear evidence for elevated pore fluid pressures and hydraulic fracturing, and the pulsed nature of dolomite cementation implies a tectonic drive. Kerr (1987) commented on the likelihood that the GGF was active in the Late Carboniferous/ Permian. Argillaceous coastal plain sediments asso-... 

Mamyrin BA, Tolstikhin IN. (1984) Hehum isotopes in nature. Elsevier, Amsterdam Mann DM, Maekenzie AS (1990) Predietion of pore fluid pressures in sedimentary basins. Marine Petrol Geol 7 55-65... 

In order to predict the T-H-M response of the bentonite, a coupled T-H-M transient analysis was performed with the Finite Element Code FRACON. The governing equations incorporated in the FRACON code were derived from an extension of Biot s (1941) theory of poro-elasticity to include the T-H-M behaviour of the unsaturated FEBEX bentonite. The model formulation(Nguyen, Selvadurai and Armand, 2003) resulted in three governing equations where the primary unknowns are temperature, the displacement vector and the pore fluid pressure, as follows ... 

Relations may be developed to represent the steady pore fluid pressures that develop around a penetrometer under steady penetration, at penetration rate, U. These rtKxlels necessarily employ simple linearized constitutive relations, but incorporate the important influence of a porous medium migrating past the penetrometer tip, albeit in a simplified form. Dislocation models (Elsworth, 1991 1993) may be applied to represent a penetrometer of infinitesimal-radius, but suffer the disadvantage that penetration-induced pressures become singular at the assumed penetrometer tip. The approximate solution for a finite radius penetrometer avoids this shortcoming, as explored in the following. 

A solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a penetrometer that self-embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. Consider a lance falling through the water column that has reached terminal velocity, Uo, and subsequently impacts the soft sediments of the seabed, as illustrated in Figure 5. The non-dimensional pressure, Pd, may be used to define the build-up of pressure following the impact of the penetrometer with the surface of the seabed. The penetrometer impacts the seabed at velocity Uo, represented in dimensionless magnitude as Ud, and decelerates to arrest. Non-dimensional pressures are plotted as the product PdXd, since it is known that the peak pressures, sh-... 

The effects of temperature change on pore fluid pressure (Wang et al., 1996) is given by ... 

For all the processes and mechanisms, the major coupling parameters are stress, pore fluid pressure and temperature. 

Pore fluid pressure is sum of the partial pressures of gas (bubble phase) and liquid phases... 

Smectite group minerals, when present in the petroleum reservoirs, play an important role in the migration of hydrocarbons. At the shallow level of reservoir rocks smectite can exist, but at deeper level the increase of temperatiue transforms it to other minerals. Generally dioctahedral smectites are transformed to illite and trioctahedral smectites are transformed to chlorite, releasing the interlayer water molecules in both cases. That released water increases the pore fluid pressure that may lead to migration of the hydrocarbons. 

Healy, D. 2008. Damage patterns, stress rotations and pore fluid pressures in strike-slip fault zones. Journal of Geophysical Research-Solid Earth 113 1-16. 

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