Alkaline flooding applications

Effect of Ca2. In many reservoirs the connate waters ontain substantial quantities of divalent ions (mostly Ca . In alkaline flooding applications at low temperatures, the presence of divalent ions leads to a drastic increase in tensions r35,36]. Kumar et al. f371 also found that Ca and Mg ions are detrimental to the interfacial tensions of sulfonate surfactant systems. Detailed studies at elevated temperatures appear to be non-existent. 

Hawkins, B. F., K. C. Taylor and H. A. Nasr-El-Din, Mechanisms of Suer-factant and Polymer Enhanced Alkaline Flooding Application to David Lloydminster and Wainright Sparky Fields, JCPT 33, 52-63 (1994). 

Recent research and field tests have focused on the use of relatively low concentrations or volumes of chemicals as additives to other oil recovery processes. Of particular interest is the use of surfactants as CO (184) and steam mobility control agents (foam). Also combinations of older EOR processes such as surfactant enhanced alkaline flooding and alkaline-surfactant-polymer flooding have been the subjects of recent interest. Older technologies polymer flooding (185,186) and micellar flooding (187-189) have been the subject of recent reviews. In 1988 84 commercial products polymers, surfactants, and other additives, were listed as being marketed by 19 companies for various enhanced oil recovery applications (190). 

Both nonionic and anionic surfactants have been evaluated in this application (488,489) including internal olefin sulfonates (487, 490), linear alkylxylene sulfonates (490), petroleum sulfonates (491), alcohol ethoxysulfates (487,489,492). Ethoxylated alcohols have been added to some anionic surfactant formulations to improve interfacial properties (486). The use of water thickening polymers, either xanthan or polyacrylamide to reduce injected fluid mobility mobility has been proposed for both alkaline flooding (493) and surfactant enhanced alkaline flooding (492). Crosslinked polymers have been used to increase volumetric sweep efficiency of surfactant - polymer - alkaline agent formulations (493). 

Field Application. Field trials of classical alkaline flooding have been disappointing. Mayer et al. (60) indicated that only 2 of 12 projects had significant incremental oil recovery North Ward Estes and Whittier with 6-8 and 5-7% pore volume, respectively. Estimated recovery from the Wilmington field was 14% with a classical alkaline flooding method (61). However, post-project evaluation of that field indicated no improvement over water-flooding (62). 

This section compares different alkalis used in alkaline flooding and discussed their application advantages and disadvantages. 

Alkaline flooding is also called caustic flooding. Alkalis used for in situ formation of surfactants include sodium hydroxide, sodium carbonate, sodium orthosilicate, sodium tripolyphosphate, sodium metaborate, ammonium hydroxide, and ammonium carbonate. In the past, the first two were used most often. However, owing to the emulsion and scaling problems observed in Chinese field applications, the tendency now is not to use sodium hydroxide. The dissociation of an alkali results in high pH. For example, NaOH dissociates to yield OH" ... 

The theories of alkaline flooding and polymer flooding alone are discussed in their respective chapters. This chapter focuses on the interaction and synergy between alkali and polymer. It also presents a field application. 

Chapter 10 on alkaline flooding lists emnlsiflcation as one important mechanism in oil recovery. Experiments showed that if the color of produced fluid was dark brown, and the water color was dark yellow, the oil was emulsified. In these experiments, the oil recovery was in the range of 18 to 22%. If water and oil came out of the core alternately, and the water was clear, the oil was not emulsified. In these cases, the oil recovery was in the range of 14 to 16% (Cheng et al., 2001). In other words, emulsification increased the oil recovery factor by abont 5%. Many wells in Daqing ASP applications showed that if the produced fluids were more emulsifled, the decrease in water cut would be higher. 

Recently we have carried out laboratory tests (17, 18, 19) in which the sodium silicate was added directly to a dilute surfactant solution to recover oil. Such a process would be akin to alkaline flooding processes where a dilute surfactant is formed in-situ. In this case however the crude is lighter and does not contain the natural acids necessary to form surfactants in-situ. Therefore surfactant is injected and protected or enhanced by the sodium silicate such that a low tension waterflood is assured. Such a system is less complex and therefore more widely applicable than micellar/polymer techniques thus filling the void between the alkaline and micellar/polymer EOR processes. 

An unexpected Residual Oil Saturation (ROS) ring was observed after the application of the Polymer Augmented Alkaline Flooding (PAAF) process in linear and radial Berea sandstone cores. No information about the previous observations of this effect has been found in the literature. Such an effect was not observed in cores flooded with either alkaline solution or polymer solution alone. Thus, the formation of the ROS ring was attributed to the interaction between the alkaline/polymer blend solution and chasing fresh polymer solution at their transitional interface. 

Consequently, such an idea led to the development of a new EOR process called the "first version of Polymer Augmented Alkaline Flooding" (PAAF). In the application of this process an alkaline solution slug is injected to mobilize the residual oil, which is the oil mechanically entrapped and/or sticking on the pore walls. The alkaline solution slug is chased by a fresh polymer slug, which provides the improved mobility control and volumetric sweep efficiency to enhance oil recovery ... 

Mungan, N. "Enhanced Oil Recovery Using Water as a Driving Fluid, Part 5 - Alkaline Flooding Field Applications , World Oil, Vol. 193, No. 1, July 1981, pp 181-190. 

Mobility and leachability of diflubenzuron in soils is low, and residues are usually not detectable after 7 days. In water, half-time persistence (Tb 1/2) is usually less than 8 days and lowest at elevated temperatures, alkaline pH, and high sediment loadings (Fischer and Hall 1992) (Table 17.2). Increased concentrations of diflubenzuron in soils and waters are associated with increased application frequency, flooding of treated supratidal areas, wind drift, and excessive rainfall (Cunningham 1986). 

Most of the concepts in this polymer reprint collection are applicable to surfactant and alkaline-surfactant-polymer floods, in which mobility control is essential. Again, space limitations prevented the inclusion of papers that focus on mobility control during chemical floods. 

The general applicability of these ideas was perhaps first pointed out in the classic articles of Flood and Forland (1947) where the stability properties of a wide variety of oxyanions were correlated with the nature of the cation. Since the decomposition reaction in such cases can be viewed as the production of a smaller or more basic fragment ion plus a more molecular species, the reaction obviously will be enhanced by a more acidic or polarizing cation. For example, the stability of the COs " ion with respect to decomposition to oxide and CO2 decreases with a decrease in atomic number and hence size in either the alkali metal or the alkaline earth metal series, whereas the stability progressively decreases even more with the smaller ions Mg +, Mn +, Cd +, Pb +, Ag+, Zn +, and Fe +. Of course, the relative stabilities of the product oxides must also be considered in a quantitative comparison. Electrostatically the process can be viewed as a competition between the formation of the more stable oxide lattice (plus CO2) and the lower lattice energy of the carbonate plus the bond energy associated with CO2 + CO,3. The elimination of oxide plus SO3... 

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