Laboratory floods

The almost-total oil recovery obtained in slim tube experiments is an unrealistic measure of the oil recovery that can be obtained from oil reservoirs or even from laboratory floods of parallel cores that have different permeabilities. Roughly, a parallel-core flood might recover half of the fraction of oil obtained from a slim tube experiment, and a field flood might do well to recover half of the fraction of oil obtained in parallel-core floods (6). 

Design of field projects using surfactants selected in Step 7 and a combination of laboratory floods at reservoir conditions, computer simulators, and reservoir history matching. 

One of these branches is the evolution of current pore-level flow models into computerized simulators for testing with laboratory floods in artificial and natural porous media, followed by the development and the use of field-scale simulators for designing field tests. 

Several different laboratory floods were performed with Wilmington crude before the field test began, to supplement previous laboratory experiments with the chosen surfactant(5-7). In these studies significant increases in oil recovery were obtained with the use of surfactant (e.g., an increase from 23% OOIP without surfactant, to 35% with). 

Parsons, R. W., "Microwave Attenuation—A New Tool for Monitoring Saturations in Laboratory Flooding Experiments", SPE J. August 1975, pp. 302-310. 

It is very important in a laboratory flood or in analysing fluids in the field to have an accurate and reproducible method for detecting and assaying polymers. There are certain methods that can be used that are common to both polymers, such as radiolabelling (Szabo, 1975 Sorbie et al, 1987d) and total organic carbon (TOC) assays. However, the most common methods of assay for xanthan and HPAM use the particular chemistry of the molecules involved. In the following sections the chemical methods of analysis that have been used to detect xanthan and polyacrylamide are described. The use... 

Polymer adsorption at a liquid/solid interface is a very well-established phenomenon and has an enormous associated literature (Lipatov and Sergeeva, 1974 Parfitt and Rochester, 1983). On the evidence from porous medium flow experiments it appears that mechanical entrapment is also a reasonably well-established mechanism for polymer retention in flow through porous media. Hydrodynamic retention is a rate-dependent effect which is rather less well understood. However, this retention mechanism is not a very large contributor to the overall levels of polymer retention in porous media and, although interesting, is probably not a very important effect in field-scale polymer floods. The important point to note is that it must be understood sufficiently well in laboratory floods so that core flood results can be interpreted correctly concerning polymer adsorption and entrapment retention mechanisms. 

Field retention values are compared to polymer retention values determined in laboratory flood tests on packs of crushed reservoir core material and surface sands. As a general trend, polymer losses observed in laboratory tests are higher than those experienced in field applications. Possible interpretations are discussed. 

The success or failure of a polymer project depends on various parameters such as mobility ratio, recovery factor at the beginning of polymer flooding, and rock wettability. An essential parameter in this connection Is polymer loss in the reservoir during flooding, which may be due to adsorption, filtration, polymer retained in fluids not produced, polymer trapped in dead-end pores, or polymer clinging to rock material, among other factors. This paper presents a comparison of the retention values obtained in laboratory flood tests and actual polymer losses in selected field projects. 

This estimate indicates that dispersion of the trailing edge may be considerably less significant in a field flood than in a laboratory flood. 

If die absence of the connate water bank in the laboratory floods reflects a polymer flood mechanism or characteristic independent of scale, then the oil recovery predicted by the numerical model is conservative. 

An alternative to this process is low (<10 N/m (10 dynes /cm)) tension polymer flooding where lower concentrations of surfactant are used compared to micellar polymer flooding. Chemical adsorption is reduced compared to micellar polymer flooding. Increases in oil production compared to waterflooding have been observed in laboratory tests. The physical chemistry of this process has been reviewed (247). Among the surfactants used in this process are alcohol propoxyethoxy sulfonates, the stmcture of which can be adjusted to the salinity of the injection water (248). 

One more variation to the many methods proposed for sulfur extraction is the fire-flood method. It is a modem version of the Sickian method, by which a portion of the sulfur is burned to melt the remainder. It would be done in situ and is said to offer cost advantages, to work in almost any type of zone formation, and to produce better sweep efficiency than other systems. The recovery stream would be about 20 wt % sulfur as SO2 and 80 wt % elemental sulfur. The method was laboratory-tested in the late 1960s and patents were issued. However, it was not commercially exploited because sulfur prices dropped. 

Liquid bromine produces a mild cooling sensation on first contact with the skin. This is followed by a sensation of heat. If bromine is not removed immediately by flooding with water, the skin becomes red and finally brown, resulting in a deep bum that heals slowly. Contact with concentrated vapor can also cause bums and bflsters. Eor very small areas of contact in the laboratory, a 10% solution of sodium thiosulfate in water can neutralize bromine and such a solution should be available when working with bromine. Bromine is especially hazardous to the tissues of the eyes where severely painfiil and destmctive bums may result from contact with either Hquid or concentrated vapor. Ingestion causes severe bums to the gastrointestinal tract (62,63). 

Direct Scale-Up of Laboratory Distillation Ljficiency Measurements It has been found by Fair, Null, and Bolles [Ind. Eng. Chem. Process Des. Dev., 22, 53 (1983)] that efficiency measurements in 25- and 50-mm (1- and 2-in-) diameter laboratory Oldersbaw columns closely approach tbe point efficiencies [Eq. (14-129)] measured in large sieve-plate columns. A representative comparison of scales of operation is shown in Fig. 14-37. Note that in order to achieve agreement between efficiencies it is necessaiy to ensure that (1) tbe systems being distilled are tbe same, (2) comparison is made at tbe same relative approach to tbe flood point, (3) operation is at total reflux, and (4) a standard Oldersbaw device (a small perforated-plate column with downcomers) is used in tbe laboratoiy experimentation. Fair et al. made careful comparisons for several systems, utibzing as large-scale information tbe published efficiency studies of Fractionation Research, Inc. 

Flooding and Loading Since flooding or phase inversion normally represents the maximum capacity condition for a packed column, it is desirable to predict its value for new designs. The first generalized correlation of packed-column flood points was developed by Sherwood, Shipley, and Holloway [Ind. Eng. Chem., 30, 768 (1938)] on the basis of laboratory measurements primarily on the air-water system. 

Available in metal only, low pressure drop, low HETP, flooding limit probably higher than Raschig rings. Not much literature data available. Used mostly in small laboratory or semi-plant studies. 

On a laboratory scale it has been shown that IOS can be used in LDLs [8], in HDPs [8-10], and in various other cleaning formulations. On the industrial side, IOS has been applied as a cosurfactant in caustic flooding formulations to enhance oil recovery [11]. 

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

The state of the art in chemical oil recovery has been reviewed [1732]. More than two thirds of the original oil remains unrecovered in an oil reservoir after primary and secondary recovery methods have been exhausted. Many chemically based oil-recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil-recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. The problem lies in the inadequacy of laboratory experiments and the limited knowledge of reservoir characteristics. Field test performances of polymer, alkaline, and micellar flooding methods have been examined for nearly 50 field tests. The oil-recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined in the literature [1732]. 

G. Ma. Laboratory study on polymer flooding in oil reservoir with high salinity. Oil Gas Recovery Technol, 3(2) I,1, 33,1996. 

J. P. Salanitro, M. P. Williams, and G. C. Langston. Growth and control of sulfidogenic bacteria in a laboratory model seawater flood thermal gradient. In Proceedings Volume, pages 457-467. SPE Oilfield Chem Int Symp (New Orleans, LA, 3/2-3/5), 1993. 

Wettability is defined as "the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids" (145). Rock wettability can strongly affect its relative permeability to water and oil (145,172). Wettability can affect the initial distribution of fluids in a formation and their subsequent flow behavior. When rock is water-wet, water occupies most of the small flow channels and is in contact with most of the rock surfaces. The converse is true in oil-wet rock. When the rock surface does not have a strong preference for either water or oil, it is termed to be of intermediate or neutral wettability. Inadvertent alteration of rock wettability can strong alter its behavior in laboratory core floods (172). 

As part of the studies undertaken in our laboratory it was necessary to be able to determine quantitatively the surfactant present in large numbers of samples (> 100 per week) arising, for example, from core flooding experiments. The chosen method needed to be rapid to reduce analysis time, and to require little manipulation of the sample to reduce errors. In this paper we report the development of a method for the determination of anionic surfactants based upon autotitration and comment on the physico-chemical basis of the technique. 

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