Reservoir Rock Mechanics, Boundary Tension & Wettability PDF

RESERVOIR ROCK MECHANICS BOUNDARY TENSION & WETTABILITY 20TH July-3RD August 2019 l SCHOOL OF CHEMICAL & ENERGY ENGINEERING l FACULTY OF ENGINEERING SUMMER SCHOOL: OIL & GAS LEARNING EXPERIENCE 2019 www.utm.my Innovative · Entrepreneurial · Global www.utm.my Innovative · Entrepreneurial · Global...

RESERVOIR ROCK MECHANICS BOUNDARY TENSION & WETTABILITY 20TH July-3RD August 2019 l SCHOOL OF CHEMICAL & ENERGY ENGINEERING l FACULTY OF ENGINEERING SUMMER SCHOOL: OIL & GAS LEARNING EXPERIENCE 2019 www.utm.my Innovative · Entrepreneurial · Global www.utm.my Innovative · Entrepreneurial · Global BOUNDARY (INTERFACIAL) TENSION Boundary Tension www.utm.my Innovative · Entrepreneurial · Global 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). Surface tension = liquid and gas phase Interfacial tension = liquid & liquid phase (immiscible contact) Interfacial tension www.utm.my Innovative · Entrepreneurial · Global Interfacial tension exist when two phase are present. It is the force that holds the surface of a particular phase together and is a function of pressure, temperature and the composition of each phase. The tension of a water-hydrocarbon system varies from approximately 72 dynes/cm for water/gas system, 20 to 40 dynes/cm for water/oil system at atmospheric conditions. www.utm.my Innovative · Entrepreneurial · Global αgw = surface tension between gas and water αgo = surface tension between gas and oil αwo = interfacial tension between water and oil αws = interfacial tension between water and solid αos = interfacial tension between oil and solid αgs = interfacial tension between gas and solid Measurement www.utm.my Innovative · Entrepreneurial · Global There are various methods to measure surface tension of a liquid. One of the method consists of a platinum ring placed over the surface of liquid. Measuring the force required to separate the ring from the surface by over coming the surface tension of the water adhered to the ring as it is lifted. How Its Relate www.utm.my Innovative · Entrepreneurial · Global www.utm.my Innovative · Entrepreneurial · Global WETTABILITY SUMMER SCHOOL: OIL & GAS LEARNING EXPERIENCE 2019 Wettability Definition www.utm.my Innovative · Entrepreneurial · Global 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 www.utm.my Innovative · Entrepreneurial · Global Why Study Wettability www.utm.my Innovative · Entrepreneurial · Global 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 presence 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 hydrocarbon recovery Wetting Fluid www.utm.my Innovative · Entrepreneurial · Global • 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 partially water-wet. Non Wetting www.utm.my Innovative · Entrepreneurial · Global • 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 Adhesion Tension www.utm.my Innovative · Entrepreneurial · Global Adhesion tension is expressed as the difference between two solid-fluid interfacial tensions. Contact Angle www.utm.my Innovative · Entrepreneurial · Global The contact angle, θ, measured through the denser liquid phase, defines which fluid wets the solid surface. Oil Oil θ αos αow Water Oil αws αos AT = adhesion tension (milli-Newtons/m or dynes/cm) θ = contact angle between the oil/water/solid interface measured through the water (degrees) αos = interfacial energy between the oil and solid (milli-Newtons/m or dynes/cm) αws = interfacial energy between the water and solid (milli-Newtons/m or dynes/cm) αow = interfacial tension between the oil and water (milli-Newtons/m or dynes/cm ) Water Wet www.utm.my Innovative · Entrepreneurial · Global Water θ ΧΤos ΧΤws ΧΤws > ΧΤos ΧΤow Solid Oil ΧΤos 0° < θ < 90° If θ is close to 0°, the rock is considered to be “strongly water-wet” Oil Wet www.utm.my Innovative · Entrepreneurial · Global Water αos αos > αws θ αws αow Oil αos 90° < θ < 180° If θ is close to 180°, the rock is considered to be “strongly oil-wet” www.utm.my Innovative · Entrepreneurial · Global www.utm.my Innovative · Entrepreneurial · Global OIL-WET WATER-WET OIL Air θ θ FREE WATER θ < 90° θ OIL Oil WATER SOLID (ROCK) GRAIN BOUND WATER WATER WATER OIL OIL RIM θ > 90° θ WATER SOLID (ROCK) GRAIN FREE WATER Wettability Classification www.utm.my Innovative · Entrepreneurial · Global 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. • Occurs where oil with polar organic compounds invades a water-wet rock saturated with brine. MEASUREMENT Most common measurement techniques • Contact angle measurement method • Amott method • United States Bureau of Mines (USBM) Method www.utm.my Innovative · Entrepreneurial · Global RESERVOIR ROCK MECHANICS CAPILLARY PRESSURE 20TH July-3RD August 2019 l SCHOOL OF CHEMICAL & ENERGY ENGINEERING l FACULTY OF ENGINEERING SUMMER SCHOOL: OIL & GAS LEARNING EXPERIENCE 2019 www.utm.my Innovative · Entrepreneurial · Global SUMMER SCHOOL: OIL & GAS LEARNING EXPERIENCE 2019 Introduction www.utm.my Innovative · Entrepreneurial · Global • Capillary pressure is important in reservoir engineering because it is a major factor controlling the fluid distributions in a reservoir rock. • Observable in the presence of two immiscible fluids in contact with each other in capillary-like tubes. • The small pores in a reservoir rock are similar to capillary tubes and they usually containing two immiscible fluid phases in contact with each other. • This interface arises from two immiscible fluid cause by interfacial tension effects. • In the presence of two immiscible fluids, one of them preferentially wets the tube surface and it is called the “wetting” fluid, the other fluid is the “non-wetting” fluid. www.utm.my Innovative · Entrepreneurial · Global The pressure difference existing across the interface separating two immiscible fluids in capillaries (e.g. porous media). Pc = pnwt - pwt Where: Pc = capillary pressure Pnwt = pressure in nonwetting phase pwt = pressure in wetting phase One fluid wets the surfaces of the formation rock (wetting phase) in preference to the other (non-wetting phase). Gas is always the non-wetting phase in both oilgas and water-gas systems. Oil is often the non-wetting phase in water-oil systems. Air / Water System ∆ h θ www.utm.my Innovative · Entrepreneurial · Global Air Water • Considering the porous media as a collection of capillary tubes provides useful insights into how fluids behave in the reservoir pore spaces. • Water rises in a capillary tube placed in a beaker of water, similar to water (the wetting phase) filling small pores leaving larger pores to non-wetting phases of reservoir rock. www.utm.my Innovative · Entrepreneurial · Global The height of water in a capillary tube is a function of: • Adhesion tension between the air and water • Radius of the tube • Density difference between fluids 2 αaw cosθ 1′h = r g 1′πaw This relation can be derived from balancing the upward force due to adhesion tension and downward forces due to the weight of the fluid (see ABW pg 135). The wetting phase (water) rise will be larger in small capillaries. Height of water rise in capillary tube, cm Interfacial tension between air and water, αaw dynes/cm = Air/water contact angle, degrees θ r = Radius of capillary tube, cm g = Acceleration due to gravity, 980 cm/sec2 Density difference between water and air, gm/cm3 1′πaw = Contact angle, θ, is measured through the more dense phase (water in this case). 1′h = = www.utm.my Innovative · Entrepreneurial · Global 1 2 AIR WATER 3 4 www.utm.my Innovative · Entrepreneurial · Global 1′h pa1 pw1 Air pa2 pw2 Water Water rise in capillary tube depends on the density difference of fluids. Pa2 = pw2 = p2 pa1 = p2 - πa g 1′h pw1 = p2 - πw g 1′h Pc = pa1 - pw1 = πw g 1′h - πa g 1′h = 1′π g 1′h www.utm.my Innovative · Entrepreneurial · Global • Combining the two relations results in the following expression for capillary tubes: 2 χρaw cos θ Pc = r Oil/Water System www.utm.my Innovative · Entrepreneurial · Global From a similar derivation, the equation for capillary pressure for an oil/water system is 2 χρow cos θ Pc = r Pc = Capillary pressure between oil and water χρow = Interfacial tension between oil and water, dyne/cm θ = Oil/water contact angle, degrees r = Radius of capillary tube, cm www.utm.my Innovative · Entrepreneurial · Global DRAINAGE Drainage Pd Mobility of nonwetting fluid phase increases as nonwetting phase saturation increases • Fluid flow process in which the saturation of the wetting phase increases • Mobility of wetting phase increases wetting phase saturation increases as Si = irreducible wetting phase saturation Sm 0.5 Swt • Four Primary Parameters Imbibition 0 Fluid flow process in which the saturation of the nonwetting phase increases IMBIBITION Pc Si • Sm = 1 - residual non-wetting phase saturation 1.0 Pd = displacement pressure, the pressure required to force non-wetting fluid into largest pores λ = pore size distribution index; determines shape Drainage Drainage Fluid flow process in which the saturation of the nonwetting phase increases. Examples: Hydrocarbon (oil or gas) filling the pore space and displacing the original water of deposition in water-wet rock Waterflooding an oil reservoir in which the reservoir is oil wet Gas injection in an oil or water wet oil reservoir Pressure maintenance or gas cycling by gas injection in a retrograde condensate reservoir Evolution of a secondary gas cap as reservoir pressure decreases www.utm.my Innovative · Entrepreneurial · Global Imbibition Process Imbibition • Fluid flow process in which the saturation of the wetting phase increases. • Mobility of wetting phase increases as wetting phase saturation increases. Examples: Accumulation of oil in an oil wet reservoir. Waterflooding an oil reservoir in which the reservoir is water wet. Accumulation of condensate as pressure decreases in a dew point reservoir. www.utm.my Innovative · Entrepreneurial · Global Pc vs. Sw Function Reflect to reservoir quality www.utm.my Innovative · Entrepreneurial · Global Permeability Effect www.utm.my Innovative · Entrepreneurial · Global 20 Capillary Pressure 16 Decreasing Permeability, Decreasing λ 12 C B A 8 4 0 0 0.2 0.4 0.6 Water Saturation 0.8 1.0 Capillary pressure, psia Grain Size Distribution Well-sorted Poorly sorted Decreasing λ Water saturation, % www.utm.my Innovative · Entrepreneurial · Global www.utm.my Innovative · Entrepreneurial · Global