1、Boundary Tension and Wettability,Immiscible Phases,Earlier discussions have considered only a single fluid in the pores porosity permeability Saturation: fraction of pore space occupied by a particular fluid (immiscible phases)Sw+So+Sg=1 When more than a single phase is present, the fluids interact
2、with the rock, and with each other,DEFINITION OF INTERFACIAL TENSION,Interfacial (boundary) tension is the energy per unit area (force per unit distance) at the surface between phases Commonly expressed in milli-Newtons/meter (also, dynes/cm),BOUNDARY (INTERFACIAL) TENSION,Modified from PETE 311 Not
3、es,DEFINITION OF WETTABILITY,Wettability is the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids. Wettability refers to interaction between fluid and solid phases.,Reservoir rocks (sandstone, limestone, dolomite, etc.) are the solid surfaces
4、Oil, water, and/or gas are the fluids,WHY STUDY WETTABILITY?,Understand physical and chemical interactions betweenIndividual fluids and reservoir rocksDifferent fluids with in a reservoirIndividual fluids and reservoir rocks when multiple fluids are presentPetroleum reservoirs commonly have 2 3 flui
5、ds (multiphase systems)When 2 or more fluids are present, there are at least 3 sets of forces acting on the fluids and affecting HC recovery,DEFINITION OF ADHESION TENSION,Adhesion tension is expressed as the difference between two solid-fluid interfacial tensions.,A negative adhesion tension indica
6、tes that the denser phase (water) preferentially wets the solid surface (and vice versa).An adhesion tension of “0” indicates that both phases have equal affinity for the solid surface,CONTACT ANGLE,The contact angle, q, measured through the denser liquid phase, defines which fluid wets the solid su
7、rface.,AT = adhesion tension, milli-Newtons/m or dynes/cm) = contact angle between the oil/water/solid interface measured through the water, degrees os = interfacial energy between the oil and solid, milli-Newtons/m or dynes/cm ws = interfacial energy between the water and solid, milli-Newtons/m or
8、dynes/cm ow = interfacial energy (interfacial tension) between the oil and water, milli-Newtons/m or dynes/cm,Wetting phase fluid preferentially wets the solid rock surface. Attractive forces between rock and fluid draw the wetting phase into small pores. Wetting phase fluid often has low mobile. At
9、tractive forces limit reduction in wetting phase saturation to an irreducible value (irreducible wetting phase saturation). Many hydrocarbon reservoirs are either totally or partially water-wet.,WETTING PHASE FLUID,Nonwetting phase does not preferentially wet the solid rock surface Repulsive forces
10、between rock and fluid cause nonwetting phase to occupy largest pores Nonwetting phase fluid is often the most mobile fluid, especially at large nonwetting phase saturations Natural gas is never the wetting phase in hydrocarbon reservoirs,NONWETTING PHASE FLUID,WATER-WET RESERVOIR ROCK,Reservoir roc
11、k is water - wet if water preferentially wets the rock surfaces The rock is water- wet under the following conditions: ws osAT 0 (i.e., the adhesion tension is negative)0 90If is close to 0, the rock is consideredto be “strongly water-wet”,WATER-WET ROCK,Adhesive tension between water and the rock s
12、urface exceeds that between oil and the rock surface.,0 q 90,OIL-WET RESERVOIR ROCK,Reservoir rock is oil-wet if oil preferentially wets the rock surfaces. The rock is oil-wet under the following conditions: os ws AT 0 (i.e., the adhesion tension is positive) 90 180If is close to 180, the rock is co
13、nsidered to be “strongly oil-wet”,OIL-WET ROCK,90 q 180,The adhesion tension between water and the rock surface is less than that between oil and the rock surface.,From Amyx Bass and Whiting, 1960; modified from Benner and Bartel, 1941,INTERFACIAL CONTACT ANGLES, VARIOUS ORGANIC LIQUID IN CONTACT WI
14、TH SILICA AND CALCITE,GENERALLY,Silicate minerals have acidic surfacesRepel acidic fluids such as major polarorganic compounds present in some crude oilsAttract basic compoundsNeutral to oil-wet surfaces,Carbonate minerals have basic surfacesAttract acidic compounds of crude oilsNeutral to oil-wet s
15、urfaces,Tiab and Donaldson, 1996,Caution: these are very general statements and relations that are debated and disputed by petrophysicists.,WATER-WET,OIL-WET,OIL-WET,WATER-WET,Brown, G.E., 2001, Science, v. 294, p. 67-69,WETTABILITY IS AFFECTED BY:,Composition of pore-lining mineralsComposition of t
16、he fluidsSaturation history,WETTABILITY CLASSIFICATION,Strongly oil- or water-wettingNeutral wettability no preferential wettability to either water or oil in the pores Fractional wettability reservoir that has localareas that are strongly oil-wet, whereas mostof the reservoir is strongly water-wet-
17、 Occurs where reservoir rock have variable mineral composition and surface chemistryMixed wettability smaller pores area water-wetare filled with water, whereas larger pores areoil-wet and filled with oil- Residual oil saturation is low- Occurs where oil with polar organic compoundsinvades a water-w
18、et rock saturated with brine,IMBIBITION,Imbibition is a fluid flow process in which the saturation of the wetting phase increases and the nonwetting phase saturation decreases. (e.g., waterflood of an oil reservoir that is water-wet). Mobility of wetting phase increases as wetting phase saturation i
19、ncreases mobility is the fraction of total flow capacity for a particular phase,WATER-WET RESERVOIR, IMBIBITION,Water will occupy the smallest poresWater will wet the circumference of most larger poresIn pores having high oil saturation, oil rests on a water filmImbibition - If a water-wet rock satu
20、rated with oil is placed in water, it will imbibe water into the smallestpores, displacing oil,OIL-WET RESERVOIR, IMBIBITION,Oil will occupy the smallest poresOil will wet the circumference of most larger poresIn pores having high water saturation, water rests on anoil filmImbibition - If an oil-wet
21、 rock saturated with water isplaced in oil, it will imbibe oil into the smallestpores, displacing watere.g., Oil-wet reservoir accumulation of oil in trap,DRAINAGE,Fluid flow process in which the saturation of the nonwetting phase increases Mobility of nonwetting fluid phase increases as nonwetting
22、phase saturation increases e.g., waterflood of an oil reservoir that is oil-wetGas injection in an oil- or water-wet reservoirPressure maintenance or gas cycling by gas injectionin a retrograde condensate reservoir Water-wet reservoir accumulation of oil or gas in trap,IMPLICATIONS OF WETTABILITY,Pr
23、imary oil recovery is affected by the wettability of the system. A water-wet system will exhibit greater primary oil recovery.,WATER-WET,OIL-WET,IMPLICATIONS OF WETTABILITY,Oil recovery under waterflooding is affected by the wettability of the system. A water-wet system will exhibit greater oil reco
24、very under waterflooding.,From Levorsen, 1967,Effect on waterflood of an oil reservoir?,Water-Wet System,Oil-Wet System,IMPLICATIONS OF WETTABILITY,Wettability affects the shape of the relative permeability curves. Oil moves easier in water-wet rocks than oil-wet rocks.,IMPLICATIONS OF WETTABILITY,M
25、odified from Tiab and Donaldson, 1996,? p. 274,IMPLICATIONS OF WETTABILITY,Water injection, pore volumes,Modified from NExT, 1999,WETTABILITY AFFECTS:,Capillary PressureIrreducible water saturationResidual oil and water saturationsRelative permeabilityElectrical properties,LABORATORY MEASUREMENT OF
26、WETTABILITY,Most common measurement techniques Contact angle measurement method Amott method United States Bureau of Mines (USBM) Method,NOMENCLATURE,AT = adhesion tension, milli-Newtons/m or dynes/cm) = contact angle between the oil/water/solid interface measured through the water (more dense phase
27、), degrees os = interfacial tension between the oil and solid, milli-Newtons/m or dynes/cm ws = interfacial tension between the water and solid, milli-Newtons/m or dynes/cm ow = interfacial tension between the oil and water, milli-Newtons/m or dynes/cm,References,1. Amyx, J.W., Bass, D.M., and Whiti
28、ng, R.L.: Petroleum Reservoir Engineering, McGrow-Hill Book Company New York, 1960. 2. Tiab, D. and Donaldson, E.C.: Petrophysics, Gulf Publishing Company, Houston, TX. 1996. 3. Core Laboratories, Inc. “A course in the fundamentals of Core analysis, 1982. Donaldson, E.C., Thomas, R.D., and Lorenz, P.B.: “Wettability Determination and Its Effecton Recovery Efficiency,” SPEJ (March 1969) 13-20.,
