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1、WETTABILITY ALTERATIONKai Lang Huang, China University of Petroleum, Beijing Campus (CUP)AbstractWettability of rocks is a combined character reflecting the interaction between the rock mineral and the reservoir fluids, as important as other parameters such as porosity, the permeability, the saturat
2、ion, and the pore pressure. Wettability alteration, refers to the reversal of wettability of rock from oil-wet to water-wet or from water-wet to oil-wet similarly, making a great contribution to enhancing oil recovery, caused by the injected soluble surfactants mainly researched in this paper. When
3、the formation is water-wet, a large amount of oil can be drive out. This paper mainly research the mechanisms for wettability alteration, and its application in EOR and what type and kind of surfactants can be used to improve oil recovery. IntroductionWettability is evaluated by measuring water-oil
4、contact angles, when measured at different stages, different angle can obtain thus indicating the rock is oil-wet or water-wet. The term “wettability alteration”, also called “wettability reversal” refers to reversal of the wettability of a solid surface where surface-active substances are adsorbed.
5、 For example sand, are water-wet originally, but when the rock core was saturated with surface-active substance, due to adsorption, sand grain can become oil-wet. Similarly, for some rock, oil-wetting originally can also undergo a wettability alteration. Wettability alteration can take place during
6、active production stage and also depending on the variations of surface properties of grains and fluid compositions changes across the reservoir.It has been recognized that half of the worlds known oil reservoir are in carbonate reservoirs. Many of these carbonate reservoir are naturally fractured,
7、however most carbonate reservoirs(about most 80%) are oil-wet or mix-wet , thus if the formation is water-wet , the positive capitally forces helps in imbibing water into the matrix and expelling the oil out, enhancing the oil recovery by the wettability alteration during surfactant flooding or Surf
8、actant-polymer flooding in carbonate reservoirs. Hence fractured reservoir with high low matrix permeability need EOR technique to achieve maximum production, dilute surfactants with appropriated amounts are developed to dramatically improve the oil recovery from the fractured carbonates.The mechani
9、sm of the wettability alteration Wettability is a major factor in controlling the location, flow, and distribution of fluids in a reservoir. Polar crude oil components can be adsorb on mineral surfaces and alter their wetting properties. Its essential to recognize that the polar components of the cr
10、ude oils can be adsorb by several distinct mechanisms, depending on factors that include brine composition and the solvent quality of the oil for its asphaltenes. Its recognized that there exit four types of mechanical interaction. ( I ) polar interaction that predominate in the absence of a water f
11、ilm between oil and solid, ( ii ) surface precipitation .dependent mainly on crude oil solvent properties with respect to the asphaltenes, ( iii ) acid/base interaction that control surface charge at oil/water and solid/water interfaces, ( iv ) ion binding or specific interactions between charged si
12、tes and higher high valence ions. Fig a clearly shows the mechanism of the function of surfactant, it indicates that molecules of the anionic surfactant (red circles show) can be adsorb by several distinct mechanisms into the interface, while the polar components of the crude oil are also be adsorb
13、into the interface, during the spontaneous imbibition of anionic surfactants into the oil-wet carbonate, active surfactants reduce the contact angle thus alert the wettability of the rock, the capillary pressure as driving force, increase the oil production.The Effect of Wettability alteration As sa
14、turation is one of the key parameters in the calculations of the volumetric estimates of hydrocarbon reserves.it appears that all the physical properties that are related to the saturation are affected by the rocks wettability. For instance, capillary pressure curves behave differently depending on
15、the degree of wettability as depicted in fig.2 for the both water-and oil-wet rocks. In the formation the wettability affect many parameter, when the wettability reverse it will definitely cause great effect on the reservoir. Here list the relationship between the rock physical parameters (porous pl
16、ate capillary pressure. Nuclear Magnetic Resonance electrical resistivity, acoustic velocity etc.)And saturation measurements under laboratory conditions. When the wettability reverse, it will cause great change the parameters calculation for the formation.Wettability depends on the brine, oil and mineral compositions as well as temperature and other factors, if the wettability is altered to water-wet, large amount of oil can be recovered through spo
