Permeability fault

Figure 8.6 Temispack reconstruction of the present-day distribution of overpressures induced by compaction disequilibrium for two assumed conditions of fault permeability a. faults are assumed to be permeable b. faults are assumed to be impermeable (arrows Darcy velocity) (from Burrus et al., 1991, Geological Society Special Publication no. 59, Fig. 7, p. 97. Reprinted by permission).

If a fault is hydrocarbon-wet or the pressure difference across it exceeds the capillary entry pressure, it will leak and become a permeability barrier to flow. The probability that a hydro carbon column will be retained by a permeability barrier over geological time is a function of the rate of flow through the fault. In the case of Darcy flow, the rate of flow (Q) per unit area is proportional to the pressure gradient (AF/Ax) across the fault, the fault permeability (/c), and inversely proportional to the fluid viscosity (a) ... 

INVESTIGATING THE RELATIONSHIP BETWEEN FAULT PERMEABILITY AND EFFECTIVE STRESS USING CONSTRAINTS FROM RESERVOIR INDUCED... 

This research uses observations of reservoir induced seismicity (RIS) at A u reservoir. NE Brazil, to investigate the spatial and temporal evolution of effective stress in the region and its relationship to fault permeability. A u reservoir was constructed in 1983 and has a capacity of 2.4 x lO m maintained by a 34 m high earth-filled dam constructed on Precambrian shield. Annual reservoir variation is 3-6 m which results in annual seismic activity due to a proposed mechanism of pore pressure diffusion (Ferreira et al. (1995), do Nascimento et al. (2003a)). Digital data at A u... 

Keywords reservoir structures, faults, folds, depositional environments, diagenesis, geological controls, porosity, permeability... 

Compaction reduces porosity and permeability. As mentioned earlier during the introduction of growth faults. If the expulsion of pore water is prevented, overpressures may develop. 

Combination tra/ s—sedimentary trap features that result from both stratigraphic and structural mechanisms. There can be many combinations for stratigraphic and structural traps. An example of such a trap would be a reef feature overlaying a porous and permeable sandstone, but in which the sequence has been faulted (see Figure 2-54). Without the fault, which has provided an impregnable barrier, the hydrocarbons would have migrated further up dip within the sandstone. 

Other wells in the same field had shown a limestone reservoir of fair permeability, with major tectonic faults and some associated fissures. Well data were provided by the operator. The low value of the wellbore storage demonstrates no coupling of the well with secondary porosity. However, the operator suspected the presence of some kind of fault not far from Well B, whose production test was unusual. He decided to acidize in an attempt to establish communication. 

Macroscopic dispersion, on the other hand, arises from heterogeneities on a scale larger than individual pores and grains. Such heterogeneities include laminae, layers, and formations of contrasting permeability fractures larger than the microscopic ones already considered and karst channels, joints and faults. Dispersion of this sort is sometimes referred to as differential advection. 

Solubility trapping refers to the C02 that dissolves into the brine. The C02-brine solution has a density greater than brine alone, preventing buoyant flow of the C02 toward the surface, even along high-permeability vertical pathways such as faults. 

Caine, J. S., Evans, J. P. Forster, J. P. 1996. Fault zone architecture and permeability structure. Geology, 24, 1025-1028. 

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

Site 997 was drilled at the crest of the Blake-Bahama Ridge (where the strongest BSR occurs) at 450 mbsf. One large solid piece of gas hydrate was recovered from approximately 331 mbsf at a suspected small fault plane. However, the presence of more disseminated hydrates was inferred over a zone from approximately 180 to 450 mbsf. It was indicated that gas hydrate development may be extensive at this location, possibly acting as a means of sealing with permeability and porosity reduction. 

Figure 7.25 shows the position of five Leg 204 drill sites. The off-summit Site 1245 intersects an unusual horizon marked A extending from about 1600 to 1400 m (although not shown here, this fault does extend to the summit). This silty sand horizon is important because its porosity and permeability allows for rapid... 

The cold seeps of methane migration along the geologic faults or permeable stratigraphic horizons provide concentrations in excess of... 

Fig. 3.8 A fault has placed a high conducting aquifer against an igneous rock of low permeability. Water ascends along the fault zone, forming a line of springs. Only part of the faults are open and conduct groundwater flow others are clogged by compression and/or mineralization.

Zhang C. F., Tullis T. J., and Scruggs V. J. (2001) Implications of permeability and its anisotropy in a mica gouge for pore pressures in fault zones. Tectonophysics 335, 37-50. 

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