Lithology permeability

Similarly to porosity, permeability values have been constrained according to the expected range of permeability values obtained from lithologies. Permeability ranges and first modes corresponding to each seismic facies for the different geographical locations are given in Table 2. 

If appropriate, correlation panels may contain additional information such as depositional environments, porosities and permeabilities, saturations, lithological descriptions and indications of which intervals have been cored. 

Airflow may be impeded by lithological barriers or travel preferentially through high-permeability channels (or fractures). 

RELATIVELY HIGH-PERMEABILITY LITHOLOGY (CHIEFLY USCS SOIL TYPE SP)... 

In a recent ocean hydrate formation state-of-the-art summary, Trehu et al. (2006) listed the effects of fluid flow and sediment lithology. Ocean hydrate deposits are distributed on a spectrum between two types in ocean sediments (1) focused high flux (FHF) gas hydrates, and (2) distributed low flux (DLF) gas hydrates. In FHF hydrates the gas comes from a large sediment volume channeled through a high-permeability sand to the point of hydrate formation, and these hydrates are typically in the upper tens of meters of the sediment. In contrast, the DLF hydrates are generated near where the hydrates are formed, and fluid flow is responsible for movement of the gas within the gas hydrate occurrence zone (GHOZ). 

Lithology may exercise a primary control of hydrate deposition, resulting from permeability, faults, and traps. 

There are several major problems with the described approach. First, the geological maps are prepared by stratigraphic units, and the lithology has to be inferred. In any case, stratigraphic units include, in most cases, alternations of various rock types, often with a wide range of permeabilities. It is almost impossible to translate a geological map into permeability units. 

Fig. 9. Permeability versus capillary entry pressure. Entry pressure increases with decreasing permeability. The regression line drawn through the data was derived for a range of lithologies by Ibrahim et al. (1970) (Watts, 1987 Antonellini and Aydin, 1995). The relationship appears to hold for the cataclastic faults as well. Some of the deviations from the regression are due to uncertainties in the thickness of the deformation bands and slip planes, which lead to overestimated fracture permeabilities of up to one order of magnitude.

Fig. 3. Plot of displacement pressure against permeability for a wide range of undifferentiated lithologies (including shale, limestone and anhydrite) measured under in situ conditions. Dataset of Ibrahim et al. (1970).

Development of geopressure suggests that fluid movement is retarded both vertically and horizontally. This can be due to rapid burial of low-permeability sediments, rapid enough to prevent compaction water to leave the system, or lithology change, or both. Some of the important mechanisms that cause geopressure are ... 

In summary, the new technique developed at BP uses a proprietary transformation that relates velocity directly to effective stress, temperature and gross lithology, takes account of the major causes of overpressure in clastic basins (namely, undercompaction, clay dehydration and diagenesis, buoyancy and charging of fluids in dipping, permeable beds), and predicts effective stress directly, which is the most fundamental quantity for pressure prediction. 

Water-table level b.l.s. (m) Total thickness (m) and lithology of poorly permeable layer (a, b, c) ... 

Decrease in COj induced when fluids migrate to high permeability, underpressured lithologies, such as at interface between mudstones and sandstones, or along fault zones that are connected to underpressured zones. The precipitation of calcite can thus be envisaged as follows ... 

Dunn, T.L. (1995) Anisotropy and Spatial Variation of Relative Permeability and Lithologic Character of Ten-sleep Sandstone Reservoirs in the Bighorn and Wind River Basins, Wyoming. 2nd Annual Technical Report for United States Department of Energy contract no. DE-AC22-93BC14897, 114 pp. 

Aquifer layers in the underground are built up of unconsolidated formations, such as gravel, sand or silt, or semi-consolidated or fissured hard rock formations that are permeable enough to store and transmit noticeable quantities of groundwater. Therefore, the geological conditions, in particular the lithological composition, the bedding... 

Deterministic permeability models. Application of the above principles to high temperature stable isotopes was pioneered by Norton and Taylor (1979) in their models of isotopic alteration of the Skaergaard layered intrusion and its host rocks. They used discreet zones and layers to which they assigned individual permeability values. Cartwright (1997) presented two-dimensional cases in which he modeled individual high permeability networks (fractures). Cook et al. (1997) used multiple, constant permeability zones to model the distribution of lithologies in the Alta stock area (see detailed discussion below). The advantage of this approach is that the calculated stable isotope patterns can be compared directly with measured patterns provided the permeability structure is adequately known. Permeability is also a function of time. Bolton et al. 

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