The Significance of Wettability in Tight Oil Exploration and Development

oil and gas resources depletion, unconventional oil and gas resources are getting more and more attention, and have become a major contributor to the global oil and gas production growth over the past five years (Zou et al., 2012; Jia et al., 2014). After shale gas, the tight oil in the North America has get a major breakthrough in exploration and development. The tight oil is a kind of oil which accumulates in the reservoir such as dense sandstone, dense carbonate whose overburden pressure matrix permeability is less than or equal to 0.1×10μm (air permeability is less than 1×10μm)(NPC,2011; Zou et al., 2014). Preliminary evaluation shows that: tight oil resources are very rich in China, the favorable exploration area is about 18×10 km, the amount of geological resources are between 74×10 t and 80×10 t, the recoverable resources are between 20?0 t and 25×10 t (Zou et al., 2015). At present, in China, many reserves area in which the the amount of geological resources are between 5×10 t and 10×10 t have been discovered in the Triassic Yanchang Formation of Erdos Basin, Permian Lucaogou Formation of Junggar Basin, Qingshankou Formation of Songliao Basin and Fuyang oil layer; there are also many important discovery in the dense sandstone and dense carbonate of Bohai Bay area and Sichuan Basin (Jia et al., 2012; Pang et al., 2012; Cao et al., 2014; Zou et al., 2015). Compared with marine tight oil in the North America, the tight oil reservoirs in China have the strong heterogeneity, the poor distribution stability and whose enrichment process, occurrence state and flow regularity are more complex. Compared with the conventional reservoir, the tight oil reservoir have a more poor physical properties and was more difficult to be evaluated with traditional analysis and measurement method. At present, many scholars have carried out a lot of work on the space fine characterization of micro/nano pore system in the tight oil reservoir, but they are rare that the study of wettability-the surface properties of the Micro/ Nano pore system which have important significance in the mechanism research of tight oil enrichment, occurrence and flow. Therefore it is necessary to enhance the tight oil reservoir wettability study on the influencing factor and quantitative characterization to find out how it effects exploration and development of tight oil reservoir. Wetting refers to the phenomenon when liquid contact solid the liquid will spread along the solid surface (Materials Science and Technology Noun (defining version ), 2010). Wettability is a tendency of expansion or adhesion that the liquid is to solid surface when the liquid is in one mixed phase fluid, and it is one of the most important properties of surface properties of solid surface. For example air and water, if the solid surface is hydrophilic, water will spontaneously derive the air and spread on the solid surface, such as the tillandsia usneoides and sphagnum absorb water through their leaf with the upper hydrophilic (Koch et al., 2009); if the solid surface is hydrophobic, water is not easy to spread out in the solid surface, such as, water on the lotus leaf surface spontaneously gathered into a ball and is easy to rolling off (Barthlott et al., 1997). Study on the wettability of rock mainly plays a role in three aspects in the exploration and development of Oilfield: