Formation-water displacement

FIGURE 6.4 Steam flooding is one of two principal thermal methods for oil recovery and has been commercially applied since the early 1960s. A mixture of steam and hot water is continuously injected into the oil-bearing formation to displace mobilized oil to adjacent production wells. Reprinted with permission from Enhanced Oil Recovery. Copyright 1984 by the National Petroleum Council. 

Earlier corrosion inhibitors limited the maximum strength of the acid to 15% by weight. Improved corrosion inhibitors (see below) have made the use of higher acid concentrations, such as 28% HCl more common. More dilute solutions may initially be injected in sandstone acidizing to reduce the formation of insoluble sodium and potassium fluorosilicates by displacing saline formation water before injection of hydrochloric acid. 

A series of processes will control the behaviour of C02 in saline aquifer formations. First, the C02 will displace the formation water (brine) originally in place and will lead to a local increase in pore fluid pressure (van der Meer, 1992). The injected C02 will not be distributed evenly, but will finger out, owing to the lower density than the pore waters and the heterogeneities of the aquifer. Doughty et al. (2001) point out that the shape of the C02 plume in the aquifer will be highly site- and case-specific. Carbon dioxide will rise to the top of the aquifer and migrate at the bottom of the... 

Although formation waters show a wide range in isotopic composition, waters within a sedimentary basin are usually isotopically distinct. As is the case with surface meteoric waters, there is a general decrease in isotopic composition from low to high latitude settings (Fig. 3.20). Displacements of 5D and 8 0-values from the Meteoric Water Line (MWL) are very often correlated with salinity the most depleted waters in D and O are usually the least saline, fluids most distant from the MWL tend to be the most saline. 

Methanol co-adsorbed with water displaced most of the water on the surface methanol co-adsorbed with oxygen formed surface methoxides stable to 625 K. Oxygen pretreatment of the surface did lead to the formation of a species assigned as formaldehyde, which Henderson proposed to be formed via a disproportionation reaction between two methoxides. Spectroscopic probes of the controlling intermediate were inconclusive [71,72]. 

In a dehydrated state, the frequency corresponding to the PO2 group asymmetric mode of vibration is 1237 run. Upon full hydration (18 to 20 water molecules per lipid) the frequency decreases to 1211 nm because of the formation of hydrogen bonds with the water molecules. When fully hydrated lipids are subjected to a hypertonic shock by the addition of polyethylene glycol (PEG), the frequency increases in 6 nm, indicating a small but significant water displacement from the phosphate regions. 

Whenever ion exchange resins are regarded as insoluble acids, bases or salts, the process of ion exchange can be regarded as salt formation and displacement. The interior of a water-... 

Biogenic degradation of petroleum and its precursors may lead to the production of CAA this can occur at temperatures of up to 82°C, providing oxygen or sulfate and water are present (7.53). and may lead to the production of significant quantities of CAA (2). Water-washing of crude petroleum by relatively-fresh meteoric water may displace CAA from the oil phase to the aqueous phase (8.35). This was tested in a series of experiments (54), however, the compositions of the water washes were fairly dissimilar from those of the formation waters from the same basin (54). The CAA analyzed in this study comprised much less than 1% of the crude petroleum sample and do not represent the total CAA present. By comparison, CAA have been reported up to 3% in some crude oils (55.56). 

Initially, with the completion of development wells, such fields, for a short time, give high yields of oil accompanied by a sharp drop in reservoir pressure. During that stage, the elastic forces of viscous oil and the energy of dissolved gas constitute the principal reservoir drives. Bound formation water also assists in displacing the oil from the reservoir by weakening the forces of molecular adhesion betwen the oil and the rocks. 

The mechanism of displacement of superviscous crudes from reservoirs of different geological characteristics is not yet fully understood. The oil fields subject to this particular study all belong to strata of Miocene age. These reservoirs either do not have any aquifer drive or else their contact with formation water present outside of the oil trap is limited. Therefore, their water drive is weak and they produce essentially by dissolved gas drive. Application of new EOR methods called for detailed study of geological characteristics of the oil field and for the determination of permeabilities of its reservoir rocks. The dominance of the dissolved gas drive and the absence of the aquifer drive in most of the oil fields in question were also taken into account. 

Formation water recovered from the Zybza field was used as the oil-displacing liquid. 

Thus, as Fig. 11 indicates, the viscosity of degassed oil decreases most within the temperature range of 30-12(K C above that range, it decreases only slightly. Fig. 12 shows that coefRcients of oil displacement drop off sharply as oil viscosity increases from 22 to 150 centipoise above that viscosity ran they tend to stabilize. Consequently, in application of thermal EOR methods, oil viscosity exerts great influence on the recovery factor. Moreover, with increase in formation temperature, oil viscosity decreases in much greater degree than the viscosity of formation water. 

When cold water is used, the displacement mechanism basically depends on the surface molecular and capillary processes occurring in the bed. In their turn, these processes are controlled by the properties of the crude, the formation water, and the reservoir rocks. For one thing, the dimension of pore openings is not uniform. Furthermore, there is a great difference between the viscosity of the crude and of the water. Because of these two factors, water can move through the... 

At first the reservoir modeT was saturated with degassed crude oil. Then the oil was displaced from the bed to a fixed degree by formation water. The degree of water invasion of the model was varied by about 10-12% from one experiment to the next, ranging from 14.5 to 75.8% for the entire test series. Once the assigned degree of water encroachment was attained for a particular experiment, the temperature of the formation was stabilized at the desired level by thermostatic controls. The tests were carried out at temperatures of 100°C, 125°C, 150°C, and 200°C. In each case, prior to the temperature stabilization, any hydrodynamic connection and intake into the formation from outside was cut ofr. The reservoir outlet could be opened as required. 

With the temperatures kept constant (at 125°C, 150°C, or 200°C), the oil yield at first increases with the degree of water saturation. Maximum oil recovery, amounting to 53-55%, was attained when the degree of water invasion of the model equaled about 35%. Within these limits of bed saturation by formation water, enough heat is brought in with the steam to convert part of the formation water also to steam. The resultant pressure increase within the bed model, in its turn, favored oil displacement from the porous reservoir. 

The above studies showed that steaming of reservoir or of the near bottomhole zones of the wells has greatest effectiveness when the reservoir saturation by formation water does not exceed 40-50%. At these levels of water invasion, petroleum can be very effectively displaced even at relatively low temperatures of 125-150°C. At higher degrees of water saturation of the formation, the bottomhole zones must be heated to higher temperatures in order to maintain the same oil yield. These higher temperatures are necessary in order to reduce the viscosity of oil in the formation and to increase its phase mobility. 

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