Permeability zones

In some cases when drilling fluids invade a very low permeability zone, pressure equalisation in the formation can take a considerable time. The pressure recorded by the tool will then be close to the pressure of the mud and much higher than the true formation pressure. This is known as supercharging. Supercharging pressures indicate tight formation, but are not useful in establishing the true fluid pressure gradient. 

Permeability. Permeable zones can be identified with the resistivity measurements made with different radius of investigation. A departure between the curves of deep and shallow investigation is a qualitative indication of permeability. 

Equivalent mud weight 14 Ib/gal. The mud specific weight should be increased to 14.5 Ib/gal to avoid a kick in the next permeable zone. 

Cold groundwaters descend to the permeable zones. Mixing of the deep fluids with the cold waters brings about a rapid decrease in temperature and there by results in the precipitation of Fe-rich chlorite of about 0.5 of Fe/Fe - - Mg ratio. 

Differential pressure sticking occurs when the drill pipe becomes imbedded in the mud wall cake opposite a permeable zone. The difference between the hydrostatic pressure in the drill pipe and the formation pressure holds the pipe in place, resulting in a sticking pipe. Differential sticking may be prevented, and a stuck drill bit may be freed, using an oil-mud or an oil- or water-based surfactant composition. 

Oil recovery can also be affected by extreme variations in rock permeability, such as when high-permeability thief zones between injectors and producers allow most of the injected drive fluid to channel quickly to producers, leaving oil in other zones relatively unrecovered. A need exists for a low-cost fluid that can be injected into such thief zones (from either injectors or producers) to reduce fluid mobility, thus diverting pressure energy into displacing oil from adjacent lower-permeability zones. 

The foam, having a viscosity greater than the displacing medium, will preferentially accumulate in the well-swept and/or higher permeability zones of the formation. The displacing medium is thus forced to move into the unswept or underswept areas of the formation. It is from these latter areas that the additional oil is recovered. However, when a foam is used to fill a low oil content area of the reservoir, the oil contained therein is, for all practical purposes, lost. This is because the foam functions to divert the displacement fluid from such areas [1574-1576]. 

Selective plugging of highly permeable zones by injecting slime-forming bacteria followed by sucrose solution that turns on the production of extracellular slimes... 

Silicate gel enhances the sweep efficiency of a waterflood, gasflood, or steamflood operation by reducing the permeability of the high-permeability zones. Weak acids may be added to control gel generation rate [377]. 

T. P. Lockhart and G. Burrafato. Method and composition for reducing the permeability of a high permeability zone in an oil reservoir. Patent EP 390280, 1990. 

Asymmetric membranes have a tight, low-permeability, retentive zone that performs the desired separation and a more open, high-permeability zone that provides mechanical strength to the overall membrane. This structure is particularly critical to the economic viability of reverse-osmosis membranes. Asymmetric membranes operated in TFF mode must have the tight side facing the feed channel so that particles are retained on its surface and can be acted upon by the tangential flow. Asymmetric membranes operated in NFF mode can... 

Figure 18.24 2" 1 SPEproblem with 15 permeability zones and using all measure-...

Layer True Permeability Zone Estimated Permeability Standard Deviation (%)... 

Figure 18.26 Observed and calculated bottom-hole pressure and reservoir pressures at layers 7 and 8 for the 2" SPE problem using 7 permeability zones [reprinted from the Journal of the Canadian Petroleum Technology with permission].

The soil used in the experiment was a low plasticity sandy material with a PI of about 11%. The variations in hydraulic conductivity probably reflected zones of material that contained more sand in some places and more clay in others. Tests have been performed on a couple of liners in the field where liquid flowing into the soil liners has been dyed and traced by cutting a cross section or trench through the liner. The result seems to indicate that dyed liquid finds a defect in the top lift, moves down and spreads along a more permeable zone between lifts finds another defect, moves downward, spreads finds another defect and so forth. 

The use of polyethylene glycol ethers in a process in which a high viscosity emulsion is formed on contact with residual crude oil has also been tested as a means of plugging thief zones using surfactants (248-250). Precipitation of sodium pectate when fresh water solutions contact brine has been proposed as a method of plugging high permeability zones (251). 

Electrostatic repulsion of the anionic carboxylate groups elongates the polymer chain of partially hydrolyzed polyacrylamides increasing the hydrodynamic volume and solution viscosity. The extensional viscosity is responsible for increased resistance to flow at rapid flow rates in high permeability zones (313). The screen factor is primarily a measure of the extensional (elonga-tional) viscosity (314). The solution properties of polyacrylamides have been studied as a function of NaCl concentra-tion and the parameters of the Mark-Houwink-Sakaruda equation calculated... 

Other experiments are planned to study the location, distribution and resuscitation of ultramicrobacteria in large three-dimensional sandpacks. Such studies will allow a more realistic approximation of reservoir conditions than the unidirectional core studies. We do not consider that the ultramicrobacteria will reach or grow in areas where residual oil is located. Selective plugging involves blocking the high permeability zones already drained of oil. We consider that the injection of ultramicrobacteria will be carried, like waterflood operations, to the areas of the strata already drained of oil and permit them to disperse through pore spaces and resuscitate in these areas. 

A field experiment in a migration study of technetium in the form of TcOj was carried out by Landstrom et al. [64] who injected Tc and radioactive 82Br (non-sorbing tracer) in a highly permeable zone at a borehole. After 10 hours, breakthrough of the tracer was measured, but no retardation, i.e. no reduction of Tc, was observed in comparison with 82Br. 

Above the water table, groundwater can also occur in perched aquifer conditions. In these instances, groundwater occurs in relatively permeable soil that is suspended over a relatively low permeability layer of limited lateral extent and thickness at some elevation above the water table. Perched groundwater occurrences are common within the vadose zone high-permeability zones overlie low-permeability zones of limited lateral extent in unconsolidated deposits. However, perched conditions can also occur within low-permeability units overlying zones of higher permeability in both unconsolidated and consolidated deposits. In the latter case, for example, a siltstone or clay stone overlies jointed and fractured bedrock such that groundwater presence reflects the inability of the water to drain at a rate that exceeds replenishment from above. 

Liquid phase migration and retention — NAPL held suspended by the water table or capillary fringe or perched above low permeability zones (water wet soil) in the unsaturated zone. 

Air sparging Injects air below the water table and captures it above the water table to extract volatile contaminants and promote biodegradation Can be inefficient in low-permeability zones and complex geologic settings Typically limited to depths less than 30 ft Multicomponent mixtures can adversely affect extractability... 

Steam-enhanced extraction Injects steam above and/or below water table to promote volatilization of contaminants Can be inefficient in low permeability zones or complex geologic settings... 

In situ bioremediation Pumps nutrients through subsurface to promote growth of Can be inefficient in low-permeability zones and complex... 

In situ chemical treatment Injects chemicals to transform contaminants in place Inefficient in low-permeability zones and complex geologic... 

For over a decade, LNAPL occurrence has been investigated beneath an active refinery site in southern California. Numerous monitoring wells along with LNAPL samples have been used to evaluate the extent and character of LNAPL occurrence. LNAPL was found to occur as five pools. The main pools each consist of individual accumulations of distinct product types occurring under both perched and water table conditions. Two different recovery and mitigation strategies have been utilized. In relatively high permeability zones, a system of two-pump recovery wells was used to recover fluids recovered water is reinjected without treatment. In relatively low permeability zones, a system of one-pump recovery wells was used. In the latter case, recovered water is treated prior to disposal. 

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