In layered reservoir

PERMEABILITY IN LAYERED RESERVOIRS FIELD EXAMPLES AND MODELS ON THE EFFECTS OF HYDROFRACTURE PROPAGATION... 

Brenner, S.L. Gudmundsson, A. 2001. Permeability development during hydrofracture propagation in layered reservoirs. Norges Ge-ologiske Unders0kelse Bulletin 439 pp. 71-77. 

Bioturbation, due to the burrowing action of organisms, may connect sand layers otherwise separated by clay laminae, thus enhancing vertical permeability. On the other hand, bioturbation may homogenise a layered reservoir resulting in an unproducible sandy shale. 

Shallow marine/ coastal (clastic) Sand bars, tidal channels. Generally coarsening upwards. High subsidence rate results in stacked reservoirs. Reservoir distribution dependent on wave and tide action. Prolific producers as a result of clean and continuous sand bodies. Shale layers may cause vertical barriers to fluid flow. 

In abnormally pressured reservoirs, the continuous pressure-depth relationship is interrupted by a sealing layer, below which the pressure changes. If the pressure below the seal is higher than the normal (or hydrostatic) pressure the reservoir is termed overpressured. Extrapolation of the fluid gradient in the overpressured reservoir back to the surface datum would show a pressure greater than one atmosphere. The actual value by which the extrapolated pressure exceeds one atmosphere defines the level of overpressure in the reservoir. Similarly, an underpressured reservoir shows an pressure less than one atmosphere when extrapolated back to the surface datum. 

Reservoir pressure is measured in selected wells using either permanent or nonpermanent bottom hole pressure gauges or wireline tools in new wells (RFT, MDT, see Section 5.3.5) to determine the profile of the pressure depletion in the reservoir. The pressures indicate the continuity of the reservoir, and the connectivity of sand layers and are used in material balance calculations and in the reservoir simulation model to confirm the volume of the fluids in the reservoir and the natural influx of water from the aquifer. The following example shows an RFT pressure plot from a development well in a field which has been producing for some time. 

In stacked reservoirs, such as those found in deltaic series, it is common to find that some zones are not drained effectively. Through-casing logs such as thermal neutron and gamma ray spectroscopy devices can be run to investigate whether any layers with original oil saturations remain. Such zones can be perforated to increase oil production at the expense of wetter wells. 

If gas export or disposal is a problem gas re-injection into the reservoir may be an alternative, although this implies additional compression facilities. Gas production may be reduced using well intervention methods similar to those described for reducing water cut, though in this case up-dip wells would be isolated to cut back gas influx. Many of the options discussed under water treatment for multi-layered reservoirs apply equally well to the gas case. 

Oil reservoirs are layers of porous sandstone or carbonate rock, usually sedimentary. Impermeable rock layers, usually shales, and faults trap the oil in the reservoir. The oil exists in microscopic pores in rock. Various gases and water also occupy rock pores and are often in contact with the oil. These pores are intercoimected with a compHcated network of microscopic flow channels. The weight of ovedaying rock layers places these duids under pressure. When a well penetrates the rock formation, this pressure drives the duids into the wellbore. The dow channel size, wettabiUty of dow channel rock surfaces, oil viscosity, and other properties of the cmde oil determine the rate of this primary oil production. 

Natural Gas Natural gas is a combustible gas that occurs in porous rock of the earth s crust and is found with or near accumulations of crude oil. It may occur alone in separate reservoirs, but more commonly it forms a gas cap entrapped between petroleum and an impervious, capping rock layer in a petroleum reservoir. Under high-pressure conditions, it is mixed with or dissolved in crude oil. Natural gas termed dry has less than 0.013 dmVm (0.1 gaLlOOO fF) of gasoline. Above this amount, it is termed wet. 

Oil production requires pressure from compressed gas or water to expel oil to the surface. There arc three main types of rcsci voir drives to flush oil to wells dissolved gas drive, gas-cap drive, and water drive. With a gas drive, the oil in the reservoir is saturated with dissolved gas. As pressures fall with oil production, the gas escapes from solution, expands, and propels oil to the surface. Hence it is important to control gas production so it remains available to remove the oil. With a gas-cap drive, the upper part of the reseiwoh is filled with gas, and oil lies beneath it. As oil is withdrawn, the compressed gas expands downward, pushing oil to the well bore. As with a dissolved gas drive, gas production from the gas cap should be restricted to maintain reservoir pressure to expel the oil. Finally, with a water drive, the oil lies above a layer of water. The compressed water... 

Obviously, these examples do not cover all possible management options, but they highlight the fact that a sound knowledge of the hydrodynamics is of paramount importance for a proper water quality oriented management. Reservoirs are very dynamic systems that often stratify in a multilayered fashion to produce layers of water with huge differences in their residence time [60]. In impaired reservoirs, the best option is to increase residence time of anoxic layers, and reduce it for surface water. The presence of outlets at different depths is essential in reservoirs devoted to water supply. 

In the commonest form of microbiological assay used today, samples to be assayed are applied in some form of reservoir (porcelain cup, paper dise or well) to a thin layer of agar seeded with indicator organism. The drug diffuses into the medium and after incubation a zone of growth inhibition forms, in this case as a circle around the reservoir. All other factors being constant, the diameter of the zone of inhibition is, within limits, related to the concentration of antibiotic in the reservoir. 

Isocratic linear development is the most popular mode of chromatogram development in analytical and preparative planar chromatography. It can be easily performed in horizontal chambers of all types. The mobile phase in the reservoir is brought into contact with the adsorbent layer, and then the movement of the eluent front takes place. Chromatogram development is stopped when the mobile phase front reaches the desired position. Usually 20 X 20 cm and 10 X 20 cm plates are applied for preparative separations, and this makes the migration distance equal to about 18 cm. Due to the fact that the migration distance varies with time according to the equation Z, = (Z, c, and t are the distance of the solvent front traveled, constant,... 

Volumetric sweep efficiency is determined by the permeability and wettability distribution in the reservoir and by the properties of injected fluids. Waterflooding characteristically exhibits poor volumetric sweep efficiency. The more expensive the injection fluid, the more important it is to have a high volumetric sweep efficiency so that the injected fluid contacts and thus mobilizes a larger volume of oil. High permeability streaks or layers (thief zones) and natural or induced rock fractures can channel the injected fluid through a small portion of the reservoir resulting in a low volumetric sweep efficiency. 

Carbon cpntent of reservoirs atmosphere (SJ, biosphere (Nb), mixed layer (N,J, and ocean (N0J. R is the t4C concentration of C in the reservoir and atmospheric concentration is defined as 100 percent. The I4C concentrations are corrected for isotopic fractionation to a common 8,3C = —25 per mil. K is the eddy diflusivity, and S,aC is the i3C concentration deviation from a standard. 

Aravamudhan, Rahman, and Bhansali. [70] developed a micro direct ethanol fuel cell with silicon diffusion layers. Each silicon substrate had a number of straight micropores or holes that were formed using microelec-tromechanical system (MEMS) fabrication techniques. The pores acted both as microcapillaries/wicking structures and as built-in fuel reservoirs. The capillary action of the microperforations pumps the fuel toward the reaction sites located at the CL. Again, the size and pattern of these perforations could be modified depending on the desired properties or parameters. Lee and Chuang [71] also used a silicon substrate and machined microperforations and microchannels on it in order to use it as the cathode diffusion layer and FF channel plate in a micro-PEMFC. 

Buccal dosage forms can be of the reservoir or the matrix type. Formulations of the reservoir type are surrounded by a polymeric membrane, which controls the release rate. Reservoir systems present a constant release profile provided (1) that the polymeric membrane is rate limiting, and (2) that an excess amoimt of drug is present in the reservoir. Condition (1) may be achieved with a thicker membrane (i.e., rate controlling) and lower diffusivity in which case the rate of drug release is directly proportional to the polymer solubility and membrane diffusivity, and inversely proportional to membrane thickness. Condition (2) may be achieved, if the intrinsic thermodynamic activity of the drug is very low and the device has a thick hydrodynamic diffusion layer. In this case the release rate of the drug is directly proportional to solution solubility and solution diffusivity, and inversely proportional to the thickness of the hydrodynamic diffusion layer. 

The software sends location information to the laser/mirror system, which then directs light energy to specific regions of a thin layer of photoreactive chemical (UV curable formulation) present on a movable platform in the reservoir. Simultaneously, the information package directs the system to lower the platform slowly with the cured slice of the object into the reservoir. ... 

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