Relative permeabilities.pdf

Wettability The wettability defines how a fluid adheres to the surface (or rock in the reservoir) when there are two fluids present, e.g. water and air. The angle measured through the water is the "contact angle". If it is less than 90° the rock is water wet; greater than 90° the rock is oil wet. M...

Wettability The wettability defines how a fluid adheres to the surface (or rock in the reservoir) when there are two fluids present, e.g. water and air. The angle measured through the water is the "contact angle". If it is less than 90° the rock is water wet; greater than 90° the rock is oil wet. Most reservoir rocks are water wet. 1  oil water Rock surface θ Strongly Strongly water - wet Neutral oil - wet 0 90 180 2 Irreducible Water Saturation  In a formation the minimum saturation induced by displacement is where the wetting phase becomes discontinuous.  In normal water-wet rocks, this is the irreducible water saturation, Swirr.  Large grained rocks have a low irreducible water saturation compared to small-grained formations because the capillary pressure is smaller. July 20, 3 2024  Capillary Pressure  It is the pressure difference between two immiscible fluids , the non-wetting and wetting phases , across the interface , when the two fluids are at equilibrium in a capillary tube or a porous medium : Pc = Pnwt – P wt  Capillary pressure can be positive or negative depending on the wettability preference. For water wet reservoirs , the capillary pressure is positive.  Capillarity in a porous medium is the rise of water above the free water level into the hydrocarbon zone 4  Capillary Forces Pc = capillary pressure.  = surface tension. q = contact angle. rcap = radius of capillary tube.  In a simple water and air system the wettability gives rise to a curved interface between the two fluids.  This experiment has a glass tube attached to a reservoir of water.  The water "wets" the glass. This causes the pressure on the concave side (water) to exceed that on the convex side (air). This excess pressure is the capillary pressure. 5  Capillary Forces and Rocks  In a reservoir the two fluids are oil and water which are immiscible hence they exhibit capillary pressure phenomena.  This is seen by the rise in the water above the point where the capillary pressure is zero. The height depends on the density difference and the radius of the 6 capillaries. 7 Laboratory Capillary Pressure Measurement Capillary Pressure Threshold pressure OWC FWL 0 Swir 1 Water Saturation 8  July 20, Dr. Gamal Et Toam 9 2024  July 20, Dr. Gamal Et Toam 10 2024  July 20, Dr. Gamal Et Toam 11 2024  July 20, Dr. Gamal Et Toam 12 2024  July 20, Dr. Gamal Et Toam 13 2024  July 20, Dr. Gamal Et Toam 14 2024  July 20, Dr. Gamal Et Toam 15 2024 Effect of Wettability on Relative Permeability Water Wet Oil Wet Connate Water > 20 % < 15 % Saturation Water Saturation @ Which Relative Permeabilities > 50 % < 50 % Are Equal Relative Permeability to Water @ Maximum Water < 30 % > 50 % Saturation July 20, 2024 16  Swirr irreducible water saturation It is the maximum water saturation one can sustain without having water flow occur.  Swc connate water saturation It is the water saturation existing in the reservoir at discovery. It can be greater or equal to Swirr. 17 Relative Permeability Experiment 18 EXAMPLE A core sample has a bulk volume of 120 cc and a porosity of 25 %. Initially it has a water saturation of 20 %. Water is forced through the sample to simulate a water drive recovery. When there is no oil movement from the core , a total of 15 cc of oil is obtained. Calculate the following : a. The expected oil recovery by water drive. b. The residual oil saturation. C. The water saturation @ end of the test. 19  SOLUTION  Vp Pore volume = 30 cc Vb Vp Initial water volume = 0.2x 30 = 6 cc 0.25  120 Initial oil volume = 24 cc a – oil recovery by water drive = 15/24 = 62.5 % b – residual oil volume = 24 – 15 = 9 cc Residual oil saturation = 9/30 = 30 % c – water saturation @ end of the test = 70 % 20  Wettability July 20, Dr. Gamal Et Toam 21 2024 WHICH WILL GIVE HIGHER OIL RECOVERY: OIL WET RESERVOIRS OR WATER WET RESERVOIRS ? WHY ? July 20, Dr. Gamal Et Toam 22 2024  Effect of Wettability on Oil Recovery Oil recovery is strongly 90 affected by wettability Ultimate 80 Oil Recovery , % PV For oil wet reservoirs : 1. Water breakthrough occurs 70 much earlier. Breakthrough 2. The recovery at water B.T. is small. 60 3. Significant amount of oil can be produced following 50 0 0.2 0.4 0.6 0.8 1.0 water B.T. Water wet Oil wet Cos θ July 20, Dr. Gamal Et Toam 23 2024 Capillary Pressure – Cont. σos σws Po Pw σos σws At equilibrium , the total forces acting on the interface should be equal to zero ; P  r   2r   P  r  2r   0 2 2 o ws w os P  P  2  / r o w os ws  os ws   ow cos P c  2 cos / r cap Surface tension Contact angle Radius of the capillary July 20, Dr. Gamal Et Toam 24 2024 In the oil reservoir , the capillary pressure at elevation h above the free water level is : Po  P w  g.h.  w   o  Height above FWL Transition Zone Pc Pc Po Pw OWC FWL Sw Dr. Gamal Et Toam July 20, 2024 Sw25 Interfacial and surface tension Surface tension (ST) is term used when  characterising the forces between a liquid and a gas. Interfacial Interfacial tension (IFT) is term used for tension the forces between two different liquids. In reservoirs there are three interfaces:  oil-gas (ST), water-gas (ST), and oil-water (IFT). In this course, we will use IFT (symbol=)  in a general sense – for any fluid combination Surface tension Needle “floating” in water July 20, Oil and Water Dr. Gamal Et Toam 26 2024 Interfacial Tensions and a Solid Surface When a drop of one immiscible fluid is immersed in another and comes to rest on a solid surface, the shape of the resulting interface is governed by the balance of adhesive and cohesive forces. OIL WATER  SOLID SURFACE The surface area at the fluid-fluid contact is minimized by the interaction of these forces: Cohesive forces at the fluid-fluid interface Adhesive forces at the solid-fluid interface July 20, Dr. Gamal Et Toam 27 2024 CONTACT ANGLE The angle between the fluid and solid phases is called the contact angle. Contact angles are always measured in the denser fluid phase. If  < 90° the fluid is said to “wet” the surface. If  > 90° the fluid is said to be “non-wetting”. OIL or AIR AIR MERCURY  WATER  SOLID SURFACE adhesion > cohesion  “wetting” cohesion > adhesion  “non-wetting” Water “wets” glass, mercury is “non-wetting” on a glass surface. Interfacial tension creates a curved interface between two immiscible fluids. Adhesive Tension = σ cos θ ; we will use this when discussing Dr. Gamal Et Toam July 20,capillary pressure 28 2024 WETTABILITY The wettability of a rock refers to the contact angle for the oil-brine interface. If  < 90° the reservoir is said to be “water-wet”. If  > 90° the reservoir is said to be “oil-wet”. In oilfield terminology: 0° - 70° strongly water-wet 70° - 110° intermediate wettability 110° - 180° strongly oil-wet Wettability is affected by many factors including:  fluid compositions  mineral surface properties  microbial activity  Dr. temperature Gamal Et Toam and pressure July 20, 2024 29  WATER-WET OIL-WET Oil Oil   WATER WATER July 20, Dr. Gamal Et Toam 30 2024  WATER-WET OIL-WET Air OIL Oil OIL    WATER  WATER  < 90 WATER WATER  > 90 SOLID (ROCK) SOLID (ROCK) FREE WATER OIL GRAIN GRAIN OIL RIM BOUND WATER FREE WATER 31 Ayers, 2001  Some Practical aspects of wettability General classification of rock wettability: Water-wet Oil-wet Intermediate Fractional wettability : Rocks are having many minerals with different chemical properties which leads to different types of wettabilities in different pores. Mixed wettability: larger pores are oil-wet and smaller pores are water-wet. This is associated with the initial invasion of pores with oil. At this stage, oil preferably invades the larger pores and later on asphaltene components deposit on the rock surface to form an oil-wet rock. July 20, Dr. Gamal Et Toam 32 2024 IMPLICATIONS OF WETTABILITY Oil recovery under waterflooding is affected by the wettability of the  system. A water-wet system will exhibit greater oil recovery under waterflooding.  July 20, Dr. Gamal Et Toam 33 2024 WATERFLOOD DISPLACEMENT WATER WET RESERVOIR OIL WET RESERVOIR July 20, Dr. Gamal Et Toam 34 2024  CONTACT ANGLE – HYSTERESIS IN WATER-WET RESERVOIR i > d Water Oil i Oil d Water Solid Surface Solid Surface Wetting phase is displacing Non-wetting phase is non-wetting phase displacing wetting phase (imbibition) (drainage) July 20, Dr. Gamal Et Toam 35 2024 CAPILLARY PRESSURE The effect of interfacial tension is to create a finite pressure difference between immiscible fluids called the capillary pressure: Pc = Pnw - Pw where Pw and Pnw refer to the wetting and non-wetting phases. Capillary pressure depends on the properties of the fluids and solid surfaces, wa and coswa, and the tube (i.e., pore throat) radius, r. When adhesion > cohesion, adhesive forces draw the fluid up the tube until they are balanced by the weight of the fluid column. When cohesion > adhesion, cohesive forces drag fluid down the tube until they are balanced by the weight of the head difference forcing fluid upwards. Dr. Gamal Et Toam July 20, 2024 36  CAPILLARY PRESSURE In a reservoir at initial conditions, an equilibrium exists between buoyancy forces and capillary forces. These forces determine the initial distribution of fluids, and hence the volumes of fluid in place. July 20, Dr. Gamal Et Toam 37 2024 CAPILLARY RISE z Po Pc Pw 2r oil h oil water P water P Po  P   o gh Pw  P   w gh Water rises in a capillary tube radius, r, to a height, h. The downward-acting buoyant pressure is: Po  Pw  Dgh The downward pressure on the water is resisted by the interfacial tension at the contact around the diameter of the tube. Laplace Equation (effect of interface curvature on DP across interface): 2 cos Po  Pw  r Equilibrium requires that IFT-driven force balances buoyancy-driven 2 cos 2024 July 20, force, Dr. Gamal Et hence: Toam 38 Pc  Po  Pw   Dgh r CAPILLARY RISE July 20, Dr. Gamal Et Toam 39 2024 Jahn et al., 1998 TYPICAL INTERFACIAL PROPERTIES   Fluid-Fluid System* Contact Interfacial Angle Tension (Deg) (N/m) Air-Mercury 140 0.485 Methane-Brine 0 0.072 40oAPI Oil-Brine 0 0.015 These results were obtained for a quartz solid surface. July 20, Dr. Gamal Et Toam 40 2024 TYPICAL INTERFACIAL PROPERTIES For pore-throat diameters from 1mm to 1 mm, we obtain the following capillary pressures: Pore throat dia. (mm) 1 10 100 1000 Fluid-Fluid System Pc (kPa) Methane-Brine 288 28.8 2.88 0.29 40oAPI Oil-Brine 60 6.0 0.60 0.06 July 20, Dr. Gamal Et Toam 41 2024 Rise of Wetting Phase Varies with Capillary Radius 1 2 3 4 OIL WATER July 20, Dr. Gamal Et Toam 42 2024 Ayers, 2001 OIL-WATER TRANSITION ZONE volume of phase x Dr. Gamal Et Toam July 20, Saturation of phase x is defined as: 2024 S x 43 pore volume Jahn et al., 1998  OIL-WATER TRANSITION ZONE Pc OIL hc OIL + WATER ho WATER Sw At elevations greater than the capillary head, hc, the oil saturation is (1 - Swi). At the OWC,Dr.hGamal o, the water saturation is 1. Between ho and hcJuly Et Toam the 20, saturations vary 2024 44 continuously through the capillary transition zone.  CAPILLARY PRESSURE CURVES Swi Soi The process of decreasing the wetting phase saturation is called drainage. The process of decreasing the non- Pc wetting phase saturation is called DRAINAGE imbibition. The imbibition and drainage paths are different. This effect is called hysteresis. IMBIBITION 0 0  Sw  1 1  So  0 July 20, Dr. Gamal Et Toam 45 2024 The Pc intercept is called the displacement pressure ASYMPTOTIC (IRREDUCIBLE) SATURATIONS The asymptotic minimum value of water saturation, Swi, is known as the irreducible water saturation or the connate water saturation. This represents the saturation at which there is no connected water in the pore space. The residual water exists only as droplets (oil-wet) or films coating the grains (water-wet). Water can no longer be driven out of the rock by hydraulic means. The asymptotic minimum oil saturation on the imbibition curve, Soi, is known as the irreducible oil saturation. This is the saturation at which the oil phase becomes discontinuous. The residual oil exists only as droplets (water-wet) or films coating the grains (oil- wet). Oil can no longer be driven out of the rock by hydraulic means. July 20, Dr. Gamal Et Toam 46 2024 IRREDUCIBLE SATURATIONS For water-wet reservoirs Swi is typically 20-25% (max. 40-50%). Soi is typically 15-20%. For oil-wet reservoirs Swi is usually 10-15% (min. 25%. The maximum oil saturation is 1-Swi and the minimum is Soi. The difference between the maximum and minimum oil saturations is the fractional pore volume that can flow  Movable Oil Saturation. The ratio of the movable oil saturation and the maximum oil saturation (1- Swi) is called the withdrawal efficiency (We). We = (1 - Swi - Soi) / (1 - Swi) For a typical water wet reservoir: We = (1 -.22 -.20)/(1 -.22) = 0.58 / 0.78 = 74% For a typical oil wet reservoir: Dr. Gamal Et Toam July 20, 47 We = (1 -.12 -.35)/(1 -.12) = 0.53 / 0.88 =202460%  OIL-WATER TRANSITION ZONE Pc OIL hc OIL + WATER ho WATER Sw At elevations greater than the capillary head, hc, the oil saturation is (1 - Swi). At the OWC,Dr.hGamal o, the water saturation is 1. Between ho and hcJuly Et Toam the 20, saturations vary 2024 48 continuously through the capillary transition zone. Review Effect of sorting on porosity Well sorted :  = 32% Poorly sorted :  = 17% Grains of two sizes :  = 12.5% July 20, Dr. Gamal Et Toam 49 2024  Poor sorting results in reduction in porosity () Rise of Wetting Phase Varies with Capillary Radius 1 2 3 4 OIL WATER July 20, Dr. Gamal Et Toam 50 2024 Ayers, 2001 CAPILLARY PRESSURE CURVE SHAPES The curves a,b,c have identical irreducible water saturations c Pc (Swi) and displacement pressures (Pd) but very different b saturation profiles as a result of pore-size distribution. a Pd 0 0 Sw So 0 a - well-sorted b - poorly-sorted Capillary pressures measured under c - veryJulypoorly 20, sorted Dr. Gamal Et Toam 51 drainage conditions. 2024  Reminder: This is what real pores and pore throats look like! PT = PORE THROAT P - PORE July 20, Dr. Gamal Et Toam 52 2024 Reservoir Seal Seal Fault (impermeable) Oil/water contact (OWC) Migration route Seal Seal Hydrocarbon Reservoir accumulation rock in the reservoir rock Top of maturity Dr. Gamal Et Toam Source rock July 20, 2024 53 Reservoir Seal The seal for a reservoir is usually provided by a water wet zone  with low (but finite) permeability Typically a shale  Darcy’s Law would indicate that with a finite permeability,  gravity effect alone would cause petroleum to pass upward through the seal due to density difference, over a long (geologic) time period For multiple phases flowing, flow is controlled by pressure,  gravity, and capillary pressure Effect of displacement pressure of the seal halts upward migration of  petroleum in the trap Displacement pressure of the seal can limit the total height of reservoir  July 20, Dr. Gamal Et Toam 54 2024 AVERAGING CAPILLARY PRESSURE DATA USING THE LEVERETT J-FUNCTION The Leverett J-function was originally an attempt to  convert all capillary pressure data to a universal curve A universal capillary pressure curve does not exist  because the rock properties affecting capillary pressures in reservoir have extreme variation with lithology (rock type) BUT, Leverett’s J-function has proven valuable for  correlating capillary pressure data within a lithology. July 20, Dr. Gamal Et Toam 55 2024 DEFINITION OF LEVERETT J-FUNCTION J S w   C Pc k  cos   J-Function is DIMENSIONLESS, for a particular rock type: Same value of J at same wetting phase saturation for any unit system, any two fluids, any exact value of k, (k/)1/2 is proportional to size of typical pore throat radius (remember k can have units of length2) C is unit conversion factor (to make J(Sw) dimensionless) Dr. Gamal Et Toam July 20, 2024 56 = 1 if we use SI units for Pc,  and k EXAMPLE J-FUNCTION FOR WEST TEXAS CARBONATE 10.00 9.00 Jc Jmatch 8.00 Jn1 Jn2 7.00 Jn3 6.00 J-function 5.00 4.00 3.00 2.00 1.00 0.00 July 20, 0.00 Et Toam 0.10 Dr. Gamal 0.20 0.30 0.40 0.50 0.60 0.70 57 0.80 0.90 1.00 2024 Water saturation, fraction USE OF LEVERETT J-FUNCTION J-function is useful for averaging capillary pressure data  from a given rock type from a given reservoir J-function can sometimes be extended to different  reservoirs having the same lithologies Use extreme caution in assuming this can be done  J-function is usually not an accurate correlation for  different lithologies If J-functions are not successful in reducing the scatter  in a given set of data, this suggests that you are dealing with a variation in rock type July 20, Dr. Gamal Et Toam 58 2024 Pc(Sw) Depends on k, Core Pore Petrophysical Gamma Ray Flow Core Lithofacies Plugs Types Data Log Units  vs k Capillary Pressure High Quality 5 4 3 Function moves up and right, and becomes less “L” 2 shaped as reservoir quality decreases July 20, Low Quality Dr. Gamal Et Toam 59 2024 1  Note variation in pore properties and permeability within a formation July 20, Dr. Gamal Et Toam 60 2024 Modified from Jordan and Campbell, 1984, vol. 1 LEVERETT J-FUNCTION FOR CONVERSION OF Pc DATA  C Pc k  C Pc k J(Sw )       σ cosθ   Lab  σ cosθ   Reservoir July 20, Dr. Gamal Et Toam 61 2024 Boundary Tension and Wettability 62 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 with the  rock, and with each other July 20, Dr. Gamal Et Toam 63 2024  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) July 20, Dr. Gamal Et Toam 64 2024  BOUNDARY (INTERFACIAL) TENSION Imbalanced molecular forces at phase boundaries GAS Boundary contracts to minimize size Cohesive vs. adhesion forces  LIQUID GAS SOLID Cohesive force Adhesion force Molecular Interface (imbalance of forces) LIQUID (dense phase) July 20, Dr. Gamal Et Toam 65 2024 Modified from PETE 311 Notes 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 Oil, water, and/or gas are the fluids July 20, Dr. Gamal Et Toam 66 2024  WHY STUDY WETTABILITY? Understand physical and chemical interactions between Individual fluids and reservoir rocks Different fluids with in a reservoir Individual fluids and reservoir rocks when multiple fluids are present Petroleum reservoirs commonly have 2 – 3 fluids (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 July 20, Dr. Gamal Et Toam 67 2024  DEFINITION OF ADHESION TENSION Adhesion tension is expressed as the difference between two solid-fluid  interfacial tensions. AT   os   ws    ow cos  A negative adhesion tension indicates 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 July 20, Dr. Gamal Et Toam 68 the solid surface 2024  CONTACT ANGLE Oil ow Oil  Water Oil os ws os Solid The contact angle, , measured through the denser liquid phase, defines which fluid wets the solid surface. 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 =Dr.interfacial July 20, Gamal Et Toamenergy between the water and solid, milli-Newtons/m or dynes/cm 2024 69 ow = interfacial energy (interfacial tension) between the oil and water, milli-Newtons/m or dynes/cm WETTING PHASE FLUID 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.  Attractive forces limit reduction in wetting phase  saturation to an irreducible value (irreducible wetting phase saturation). Many hydrocarbon reservoirs are either totally or  Dr. Gamal Et Toam partially water-wet. July 20, 2024 70  NONWETTING PHASE FLUID Nonwetting phase does not preferentially wet  the solid rock surface Repulsive forces 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 July 20, Dr. Gamal Et Toam 71 2024  WATER-WET RESERVOIR ROCK Reservoir rock is water - wet if water preferentially  wets the rock surfaces The rock is water- wet under the following conditions:  ws > os  AT < 0 (i.e., the adhesion tension is negative)  0 <  < 90  If  is close to 0, the rock is considered Dr. Gamal Et Toam to be “strongly water-wet” July 20, 72 2024 WATER-WET ROCK ow Oil  Water os ws os Solid 0 <  < 90 Adhesive tension between water and the rock surface exceeds that between oil and the rock surface. July 20, Dr. Gamal Et Toam 73 2024  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 <  < 180  If  is close to 180, the rock is considered to be “strongly oil-wet” July 20, Dr. Gamal Et Toam 74 2024 OIL-WET ROCK ow Water Oil  os ws os Solid 90 <  < 180 The adhesion tension between water and the rock surface is less than that between oil and the rock surface. July 20, Dr. Gamal Et Toam 75 2024  INTERFACIAL CONTACT ANGLES, VARIOUS ORGANIC LIQUID IN CONTACT WITH SILICA AND CALCITE WATER SILICA SURFACE WATER CALCITE SURFACE July 20, Dr. Gamal Et Toam 76 2024 From Amyx Bass and Whiting, 1960; modified from Benner and Bartel, 1941  GENERALLY, Silicate minerals have acidic surfaces Repel acidic fluids such as major polar organic compounds present in some crude oils Attract basic compounds Neutral to oil-wet surfaces Carbonate minerals have basic surfaces Attract acidic compounds of crude oils Neutral to oil-wet surfaces Tiab and Donaldson, 1996 Caution: these are very general statementsJulyand 20, relations Dr. Gamal Et Toam 77 that are debated and disputed by petrophysicists. 2024  WATER-WET OIL-WET Air OIL Oil OIL    WATER  WATER  < 90 WATER WATER  > 90 SOLID (ROCK) SOLID (ROCK) FREE WATER OIL GRAIN GRAIN OIL Dr. Gamal Et Toam RIM July 20, 78 2024 BOUND WATER FREE WATER Ayers, 2001  WATER-WET OIL-WET Air Oil   WATER WATER July 20, Dr. Gamal Et Toam 79 2024  From Levorsen, 1967 July 20, Dr. Gamal Et Toam 80 2024  July 20, Dr. Gamal Et Toam 81 2024 Brown, G.E., 2001, Science, v. 294, p. 67-69  n = 30 silicate and 25 carbonates n = 161 ls., dol. From Tiab and Donaldson, 1996 CONTACT ANGLE: Triber et al. CONTACT ANGLE: -Water-wet = 0 – 75 degrees -Water-wet = 0 – 80 degrees -Intermediate-wet = 75 – 105 degrees -Intermediate-wet = 80 – 100 degrees -Oil-wet = 105 – 180 degrees -Oil-wet = 100 – 180 degrees July 20, Dr. Gamal Et Toam 82 2024  WETTABILITY IS AFFECTED BY: Composition of pore-lining minerals Composition of the fluids Saturation history July 20, Dr. Gamal Et Toam 83 2024  WETTABILITY CLASSIFICATION Strongly oil- or water-wetting Neutral wettability – no preferential wettability to either water or oil in the pores Fractional wettability – reservoir that has local areas that are strongly oil-wet, whereas most of the reservoir is strongly water-wet - Occurs where reservoir rock have variable mineral composition and surface chemistry Mixed wettability – smaller pores area water-wet are filled with water, whereas larger pores are oil-wet and filled with oil - Residual oil saturation is low July 20, - Occurs where oil with polar organic compounds Dr. Gamal Et Toam 2024 84 invades a water-wet rock saturated with brine  IMBIBITION Imbibition is a fluid flow process in which the saturation of the wetting phase  aterflood increases and the nonwetting phase saturation decreases. (e.g., w of an oil reservoir that is water-wet). Mobility of wetting phase increases as wetting phase saturation increases  mobility is the fraction of total flow capacity for a particular phase  July 20, Dr. Gamal Et Toam 85 2024  WATER-WET RESERVOIR, IMBIBITION Water will occupy the smallest pores Water will wet the circumference of most larger pores In pores having high oil saturation, oil rests on a water film Imbibition - If a water-wet rock saturated with oil is placed in water, it will imbibe water into the smallest pores, displacing oil July 20, Dr. Gamal Et Toam 86 2024  OIL-WET RESERVOIR, IMBIBITION Oil will occupy the smallest pores Oil will wet the circumference of most larger pores In pores having high water saturation, water rests on an oil film Imbibition - If an oil-wet rock saturated with water is placed in oil, it will imbibe oil into the smallest pores, displacing water July 20, Dr. Gamal Et Toam 87 e.g., Oil-wet reservoir – accumulation of oil in trap 2024  DRAINAGE Fluid flow process in which the saturation of  the nonwetting phase increases Mobility of nonwetting fluid phase increases as  nonwetting phase saturation increases e.g., waterflood of an oil reservoir that is oil-wet  Gas injection in an oil- or water-wet reservoir  Pressure maintenance or gas cycling by gas injection  in a retrograde condensate reservoir Water-wet reservoir – accumulation of oil or gas in trap  July 20, Dr. Gamal Et Toam 88 2024 IMPLICATIONS OF WETTABILITY Primary oil recovery is affected by the wettability of the system.  A water-wet system will exhibit greater primary oil recovery.  July 20, Dr. Gamal Et Toam 89 2024  WATER-WET OIL-WET Air OIL Oil OIL    WATER  WATER  < 90 WATER WATER  > 90 SOLID (ROCK) SOLID (ROCK) FREE WATER OIL GRAIN GRAIN OIL Dr. Gamal Et Toam RIM July 20, 90 2024 BOUND WATER FREE WATER Ayers, 2001 IMPLICATIONS OF WETTABILITY Oil recovery under waterflooding is affected by the wettability of the  system. A water-wet system will exhibit greater oil recovery under waterflooding.  July 20, Dr. Gamal Et Toam 91 2024  Water-Wet System Oil-Wet System Effect on waterflood of an oil reservoir? July 20, Dr. Gamal Et Toam 92 2024 From Levorsen, 1967 IMPLICATIONS OF WETTABILITY Wettability affects the shape of the relative permeability curves.  Oil moves easier in water-wet rocks than oil-wet rocks.  July 20, Dr. Gamal Et Toam 93 2024  IMPLICATIONS OF WETTABILITY Core Percent Recovery efficiency, percent, Soi no silicone Wettability 1 0.00 0.649 80 2 0.020 0.176 1 3 0.200 - 0.222 2 4 2.00 - 0.250 60 3 5 1.00 - 0.333 ? Curves cut off at Fwd 100 4 p. 274 40 5 20 0 1 2 3 4 5 6 7 8 9 10 11 12 Water injected, pore volumes July 20, Dr. Gamal Et Toam 94 2024 Modified from Tiab and Donaldson, 1996 IMPLICATIONS OF WETTABILITY Squirrel oil - 0.10 N NaCl - Torpedo core (m 33 O W 663, K 0945, Swi 21.20%) Recovery efficiency, percent Spi Squirrel oil - 0.10 N NaCl Torpedo Sandstone core, after remaining in oil for 84 days (m 33.0 W 663, K 0.925, Swi 23.28%) 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 July 20, Dr. Gamal Et Toam Water injection, pore volumes 2024 95 Modified from NExT, 1999  WETTABILITY AFFECTS: Capillary Pressure Irreducible water saturation Residual oil and water saturations Relative permeability Electrical properties July 20, Dr. Gamal Et Toam 96 2024 LABORATORY MEASUREMENT OF WETTABILITY Most common measurement techniques Contact angle measurement method  Amott method  United States Bureau of Mines (USBM) Method  July 20, Dr. Gamal Et Toam 97 2024  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), 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 July 20, Dr. Gamal Et Toam 98 2024  References 1. Amyx, J.W., Bass, D.M., and Whiting, 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. 4. Donaldson, E.C., Thomas, R.D., and Lorenz, P.B.: “Wettability Determination and Its Effect on Recovery Efficiency,” SPEJ (March 1969) 13-20. July 20, Dr. Gamal Et Toam 99 2024