Method for the tertiary recovery of petroleum by flooding with hot water and an aqueous alkaline solution
This is a continuation-in-part of U.S. Pat. Application No. 760,433, filed Jan. 18, 1977, now abandoned. 
    
    
     It is known that the recovery of mineral oil deposits, and more particularly of highly viscous petroleum may be improved by flooding with hot water. The hot water heats up the deposits, whereby the viscosity of the oil is reduced and the flowability of the oil is increased. Alkaline solutions, by changing the pH in the alkaline range, effect a reduction of the interfacial oil/water tension, whereby the petroleum is detached from the surfaces of the pores of the rock and an oil-water emulsion is formed which enhances the effect of displacement and thus increases the degree to which the oil is removed. 
     A method of recovering hydrocarbons from an underground formation containing hydrocarbon by means of steam flooding is known from German laid-open Pat. No. 2,323,261, which method comprises admitting into the warm formation a mixture of steam and a small quantity of an agent which obviously is to serve the purpose of reducing the interfacial tension between condensed steam and said immiscible hydrocarbons. Also a solution of NaOH with a concentration of about from 0.1 to 0.5% by weight combined with 0.1 to 0.5% quinoline is to be used for reducing the interfacial tension. This mode of carrying out the work has the drawback that for recovering the petroleum, steam is required which must be energy-enriched; furthermore, the addition of NaOH, for example, together with quinoline or other substances is needed to reduce the interfacial tension. This mode of operation poses the danger that the emulsion thus formed may become unstable, and the uniform distribution in the steam of those substances reducing the interfacial tension may be controlled with difficulty only. 
     It is the object of the present invention to utilize the heat stored in the carrier bed after the flooding with hot water for the flooding with alkaline, water-soluble materials, and to utilize it, in addition to effect emulsion formation, by reducing the oil viscosity due to the heating of the carrier bed, thus improving the removal of the oil while at the same time maintaining the stability of the emulsion in the carrier bed. 
     A prejudice exists in this technical field against the flooding with soda lye because if Ca-- and Mg-- ions are present in the water of the deposits, hydroxides will be precipitated which may clog the deposits, and because Ca-- and Mg-- ions will render those materials ineffective which act interfacially. Surprisingly, it was found that Ca-- and Mg-- ions present in the water of the deposit will not limit the performance of the present invention even if contained in said water in higher concentrations. 
     Now, a method for the tertiary recovery of petroleum by hot water flooding or by flooding with alkaline, water-soluble materials has been found which is characterized in that after the flooding with hot water, soda lye is admitted at ambient temperature as the flooding agent into the deposit which has been heated up by the hot water, and in that upper temperature limit is adjusted only to such a degree that the resulting emulsion formed from the petroleum together with the soda lye will practically remain stable. 
     It was found further that the temperature of the deposit, when it is above that temperature at which the emulsion is forming from the petroleum and the alkaline, water-soluble materials, may be reduced by interrupting the hot water flooding, or by admitting cold water, to such a temperature at which the forming emulsion will practically remain stable. 
     It was found further that the flooding with soda lye is carried out continuously preferably with a soda lye concentration within the range of 0.05 to 10% by weight per total weight of solution. 
     It was found further that the flooding with soda lye is preferably carried out discontinuously. 
     It was found further that after a cushion of alkaline solution, flooding is carried out with water as the flooding agent. 
     It was found further that the present method is applied also to deposits containing Ca-- and Mg-- ions in the water of the deposit. 
    
    
     The method of the present invention is explained further with the help of examples 1 and 2 without being limited to said examples. 
     The model deposits were natural sandstone granules obtained from a quarry. These granules were saturated with crude petroleum and a salt water conforming to the water of a deposit. 
     
                       TABLE                                                       
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                Example 1                                                 
                         Example 2                                        
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Rock Stratum                                                              
Length            26.5 cm    26.5 cm                                      
Diameter          5.17 cm    5.17 cm                                      
Pore Volume (PV)  115.0 ml   109.3 ml                                     
Permeability for Salt Water                                               
                  2380 md    2300 md                                      
Porosity          20.7%      19.6%                                        
Crude Oil                                                                 
Density at 40°  C.                                                 
                  0.894 kg/l 0.894 kg/l                                   
Viscosity at 40°  C.                                               
                  220 cP     230 cP                                       
Salt Water                                                                
Density at 40°  C.                                                 
                  1.089 kg/l 1.089 kg/l                                   
Viscosity at 40°  C.                                               
                  0.92 cP    0.92 cP                                      
Concentrations: NaCl                                                      
                  106 g/l    106 g/l                                      
CaCl.sub.2        27 g/l     27 g/l                                       
MgCl.sub.2        4 g/l      4 g/l                                        
Flooding                                                                  
Step 1                                                                    
Salt Water                                                                
Temperature of the                                                        
                  40° 40°  C.                               
carrier bed                                                               
Quantity          2,430 ml   2,620 ml                                     
Step 2                                                                    
Salt Water                                                                
Temperature of the                                                        
                  80° 80°  C.                               
carrier bed                                                               
Quantity          1,150 ml   1,480 ml                                     
Step 3a                                                                   
NaOH                                                                      
Concentration     4% by weight                                            
                             8% by weight                                 
Temperature of the                                                        
                  80° 80°  C.                               
carrier bed                                                               
Quantity          115 ml     22 ml                                        
Step 3b                                                                   
Salt Water                                                                
Temperature of the                                                        
                  40° 40°   C.                              
carrier bed                                                               
Quantity          700 ml     1,250 ml                                     
Remaining oil saturation                                                  
in % of pore volume                                                       
Step 1            47.2%      48.5%                                        
Step 2            45.8%      46.8%                                        
Step 3            21.2%      25.4%                                        
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     These examples show how according to the method of the present invention, the remaining oil saturation is reduced after the hot water flooding from 45.8 and 46.8% to 21.2 and 25.4%, respectively. 
     A comparative test carried out under conditions comparable to those of example 2 and comprising the use of NaOH with a concentration of 8% by weight and no heating of the carrier bed to 80° C. showed a remaining oil saturation of 41.7%.