Synthesis Of Betaine Type Surfactants And Basic Research On The Application In Oilfield

In the molecules of betaine surfactant, cationic and anionic groups coexist. In its water solution, the micelle shape and absorption behaviors on oil-water and solid-liquid interfaces could vary with the salinity and pH value, which results in the special abilities to thicken water phase, decrease interfacial intension of oil-water and reverse the wettability. Therefore, the betaine surfactant could be used as the thickener for fracturing fluid, diverting agent for acidizing and displacement agent for oil, et al.Five kinds of surfactants, i.e. octadecyl betaine(CBET-18, CBETXN-12, CBETXN-18 P CBETXN-22 J and CBETXN-22S), were synthesized in order to investigate the ability of betaine to thicken acid-used, reverse the wettability and self-diverting. Results showed that in terms of the ability to thicken acid-used, CBET-18 is the best while CBETXN-18 is the weakest when the concentrations are equivalent. However, CBETXN-18 is easier to dissolve in fresh acid than CBET-18. A diverting agent for acidizing taken CBETXN-18 as host agent and CBET-18 as supplementary agent is thus preferable. The high levels of betaine in acid-used tend to absorb on the surface of carbonatite, which could lead to the reversion of wettability on the surface of carbonatite. But since betaine and surface of carbonatite are both negative charged, the absorption between the two is not so strong. Moreover, the wettability of rock surface could be recovered by using the salt water. Overall, betaine would have no effect on the production after acidification. The parallel core evaluation experiments of steering acid found that as for the parallel core with permeability ratio lower than 5, the steering acid could enter into low permeable core and acidize it effectively, but as for that with permeability ratio being 10, the acid could not enter into the rocks and hence would not present the reversion performance. The above studies are instructive to the application of betaine to the steering acid.The oil-water interfacial intension between CBETXN-18 and four kinds of conventional heavy oils with different properties were measured. It indicated that CBETXN-18 could significantly lower the interfacial tension(10-3 mN m-1) with concentration ranges from 0.01%~0.1%. Furthermore, sand filling tube model and microscopic oil displacement simulation showed that when the aforementioned system with ultralow interfacial tension was used to displace heavy oil, obvious fingering and serious absorption of betaine on the silica sand occurred, which caused the poor oil displacement. Further studies found that addition of polymers that could improve the oil-water mobility ratio and alkali lignin that could weaken the absorption behavior and strengthen the emulsifiability of betaine would generate an efficient heavy oil displacement system.Based on the theory of regulating the boundary layer by changing the wettability of the solid surface, this paper also studied on the effect of betaine surfactants in reducing the injection pressure and enhancing oil recovery in low permeability oilfield. The wettability of the sandstone surface can be converted into lipophilicity from hydrophilicity by amphoteric surfactant!CBETXN-18 in low concentration, exhibiting a stronger ability of wettability alteration. However, amphoteric surfactant!CBETXN-18 can only reduce the oil-water interfacial tension of the crude oil with low acid value to the magnitude of 0.1 mN m-1. The liquidity experimental evaluation shows that, when CBETXN-18 was injected into the ultra-low permeability oil-core, the antihypertensive rate was only about 10%; when the CBETXN-18 above 10 pv was injected into oily core, the buck rate can reach to 20%~30%. In the paper, a composite system with extra-low interfacial tension was constructed by CBETXN-18 and small amount of alkanolamide. It is founded that, its antihypertensive behavior in the ultra-low permeability cores is similar to CBETXN-18. Above all, the performance of decreasing injection pressure and increasing injection of surfactants in ultra-low permeability cores is obvious.