Discussion About Some Factors Affecting Wettability Alteration

Abstract

Wettability alteration can change some parameters of rocks such as capillary force, permeability and electrical property. The contact angle is the most commonly and classical index of quantitative wettability measurements. According to the contact angel(water as the frame of reference), wettability can be divided into three categories:water-wet, neytrally wet, oil-wet, of which contact angel is from 0 to 75 degree, 75 to 105 degree and 105 to 180 degree, respectively. Water-wet formation is widespread and oil-wet formation is also found, so what on earth make the wettability difference? First, polar compounds in crude oils can make wettability alteration. There is a kind of low molecular weight compounds which contains both hydrophilic functional groups and hydrophobic functional groups. They dissolve in water and attract other crude oil compounds through van der waals. Water film becomes instable so that crude oil contact with formation directly and wettability alteration will occur over time. Second, when temperature and pressure change, it also can be lead to wettability alteration. They make wettability alteration through change of polar compounds properties such as solubility and rheological properties and thermodynamic properties of the surface layer. Apart from that, fluid in formation also can make wettability alteration. If pH and salinity of water become lager, the adsorption forces between crude oils and formation will get smaller and wettability can stay strong water-wet well. When the salinity of water decrease in some carbonate formation, it will occur multicomponent ionic exchange, which make polar compounds called organo-metallic complexes on the mineral surfaces disappeared for chemical reaction. And it also makes the system stay water-wet.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015