Based On Spontaneous Imbibition Impact Evaluation Method Of Tight Reservoir Wettability

The wettability of rock is the key factor in deciding the distribution and flow of reservoir fluids in rock pore,which has an important influence on oil-gas production,oil recovery and the interaction between fracturing fluid and reservoir.It is basic to have intimate knowledge of wettability of rock in oil-gas field development.Tight oil and gas reservoir is a kind of unconventional reservoir which has extremely low pore permeability and unique mineral constitution for which the evaluation method of wettability in conventional reservoir is not applicable for that in tight oil and gas reservoir.In this research,the interaction between imbibing fluid and reservoir is mainly considered and theoretical and experimental research methods are combined to analysis the specific physical properties of tight reservoir(JiLin tight sandstone reservoir)deficiency and correction method of regular droplet wettability measuring method.A method using imbibiting rate to represent wettability’s influence on flow of oil and gas is presented and the influence rule of pore wettability on flow of fluid is measured of which the micro-mechanism is analyzed.A set of conclusions is acquired:Tight oil and gas reservoir has strong spontaneous imbibiting ability which has an important effect on contact angle acquired using droplet wettability measuring method.Therefore,the wettability is both influenced by rock surface properties and its imbibiting features and changes over time.Porous medium’s spontaneous imbibiting rule is taken into consideration to correct imbibiting amount and its influence on contact angle and the measurement accuracy of surface wetting angle is enhanced.Wettability is the key factor influencing imbibiting flow of fluid in rock matrix pore which directly reflects fluid migration in pores.From the perspective of fluid migration,rock spontaneous imbibiting experiment is conducted.Combined with classic Handy model,equivalent pore wettability is presented and a method evaluating wettability quantificationally using spontaneous imbibiting curve is developed.Experimental research discovers that clay,Total Organic Carbon(TOC)and ions in fluids have important influence on rock wettability.The pore wettability in reservoir changes as a result of that clay absorbs water and organic materials which influences the spontaneous imbibiting amount and rate.Reservoir wettability is sensitive to TOC and a little amount of TOC can change rock wettability obviously.The influence of ions on pore fluid migration is monitored by Low Field Nuclear Magnetic Resonance(NMR)and the ion species and its content are showed to have important influence on wettability.Imbibition of solution with low valence and low degree of mineralization promote wettability to change-low degree of mineralization water drive.Imbibiting fluid changes Zeta potential and structure of double electrode layer resulting in thickening of water film on the surface of pores and then the wettability on the surface of rock is changed.