Fluid flow permeability barriers

A permeable reactive barrier (PRB) is defined as an in situ method for remediating contaminated groundwater that combines a passive chemical or biological treatment zone with subsurface fluid flow management. Treatment media may include zero-valent iron, chelators, sorbents, and microbes to address a wide variety of groundwater contaminants, such as chlorinated solvents, other organics,... 

The present hydrogeological framework of the sedimentary basin, which is characterized by the distribution, thickness and dip of porous and permeable hydrogeological units (aquifers/potential carrier-reservoir rocks, e.g. sands, sandstones, carbonates, fractured rocks) and poorly permeable hydrogeological units (aquitards/potential barrier rocks, e.g. shales, evaporites), and the location of geological structures and tectonic elements of importance for subsurface fluid flow, e.g. permeable or impermeable faults, unconformities... 

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) ... 

In Mesozoic sandstones on Tampen Spur and Haltenbanken, normal faults are usually characterized by grain reorientation and enrichment of clay minerals which suggest that ductile deformation dominates. Abundant quartz cement is only observed along these faults associated with stylolites. Open fractures were not present in the sandstones from Tampen Spur and Haltenbanken. Fractures in these sediments therefore normally represent permeability barriers for fluid flow. 

Calcite cementation in the Zia Formation has greatly reduced potential reservoir/aquifer quality. Most permeable units are extensively cemented with phreatic calcite. Many tabular units are often laterally extensive, forming significant barriers to vertical fluid flow and conceivably resulting in compartmentalization of the reservoir/aquifer. 

Haszeldine et al., 1992 Macaulay et al., 1993). In a number of studies particular attention has been paid to extensive calcite-cemented intervals present in many oilfields of the northern North Sea, as they may constitute permeability barriers to fluid flow. 

Fracturing and fault compartmentalization of sandstones fundamentally affects reservoir properties and may significantly influence the fluid migration pathways in a basin (Knipe, 1993). Open fractures may form high-permeability conduits, whereas cement-sealed fractures form barriers to fluid flow. Seismic, petrophysical and reservoir performance data allow regional (field-scale) effects of faulting on fluid flow to be constrained. However, much fracturing and associated cementation may occur at sub-... 

It has been stated that a filter medium is a porous (or at the very least semi-permeable) barrier placed across the flow of a suspension to hold back some or all of the suspended material. If this barrier were to be very thin compared with the diameter of the smallest particle to be filtered (and perforated with even sized holes), then all the filtration would take place on the upstream surface of the medium. Any particle smaller than the pore diameter would be swept through the pores, and any particle larger than that (assuming the particles to be rigid) would remain on the upstream surface. Some of the larger particles, however, would be of a size to settle into the individual pores and block them. The medium surface would gradually fill with pores blocked in this way, until the fluid flow reduced to below an acceptable level. At this point filtration would be stopped and the medium surface would be brushed or scraped clean (although many automatic filters have their surface continuously brushed or scraped). 

Grouted barriers use a variety of fluids injected into a rock or soil mass, which is set in place to reduce water flow and strengthen the formation. Grouted barriers are seldom used for containing groundwater flow in unconsolidated materials around hazardous waste sites because they cost more and have lower permeability than bentonite slurry walls. Nevertheless, they are suited to sealing voids in rock for waste sites remediation. 

Figure 1.2 Schematic representation of the pathway of elementary reaction ij in the traditional energetic coordinates with the activation barrier (a) and in the coordinates of thermodynamic rushes h of reactants (b). in the latter case, the reaction can be represented as a flow of a fluid between two basins separated by a membrane with permeability e-,j the examples are given for the left-to-right and right-to-left reactions (cases 1 and 3, respectively) case 2 illustrates the thermodynamically equilibrium system.

In contrast to operations discussed in all previous chapters where separation is the result of different phases in contact having different compositions, membrane separation is achieved by a membrane, or a barrier that is preferentially permeable to different species. The outcome is a process where fluids (gas or liquid) of different compositions flow on each side of the membrane. 

Loss of confinement resulting from the creation of a borehole can lead to wellbore failure. The weight of the drilling fluid provides some of the support (for the wellbore) which was originally provided by the drilled out material. However, when drilling under an overbalance condition in shales without an effective flow barrier present at the wellbore wall, invasion of the mud filtrate into the formation may occur. Due to the saturation and low permeability of shales, a small volume of mud filtrate penetrating the formation will result in a considerable increase in pore pressure near the wellbore wall. The increase in pore pressure reduces the effective mud support and can lead to a less stable wellbore condition. 

---