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1 RESISTIVITY LOGGING AND INTERPRETATION CORE Invasion and the Borehole Environment Part 1 LEARNING OBJECTIVES By the end of this lesson, you will be able to: Explain mud filtrate invasion and describe the borehole environment in terms of resistivity State the resistivities in each zone within the borehole environment Discuss the distribution of fluids in a hydrocarbon reservoir List three or more types of drilling muds and identify whether their respective filtrates are low or high resistivity Explain the effect of temperature on resistivity of a NaCl saltwater solution 1

2 SATURATION PROFILE: HYDROCARBON-BEARING ROCK SATURATION PROFILE: HYDROCARBON-BEARING ROCK 2

3 SATURATION PROFILE: INVADED ROCK SATURATION PROFILE: INVADED ROCK 3

4 SATURATION PROFILE: INVADED ROCK SATURATION PROFILE: INVADED ROCK 4

5 SATURATION PROFILE: INVADED ROCK INVASION EFFECTS Drill Mud Cake Thickness Depth of Invasion Trip Drill Rate of Invasion , ,000 Minutes after Penetration After Dewan, 1983, Fig. 1-5, p. 11 5

6 INVASION EFFECTS After Dewan, 1983, Fig. 1-5, p. 11 Drill INVASION EFFECTS Mud Cake Thickness Depth of Invasion Trip Rate of Invasion Invasion Depth Typical: 1 2 ft. ( m) Drill Range: ft ( m) , ,000 Depth of Invasion increases quickly in the first few minutes. Rate of Invasion starts fast; slows once mud cake forms. Mud Cake Thickness grows steadily; knocked off when drillpipe is tripped in. Minutes after Penetration Drill Mud Cake Thickness Depth of Invasion Trip Drill Rate of Invasion , ,000 Minutes after Penetration After Dewan, 1983, Fig. 1-5, p. 11 6

7 THE BOREHOLE ENVIRONMENT THE BOREHOLE ENVIRONMENT 7

8 THE BOREHOLE ENVIRONMENT THE BOREHOLE ENVIRONMENT Flushed zone Flushed zone 8

9 THE BOREHOLE ENVIRONMENT THE BOREHOLE ENVIRONMENT Flushed zone Flushed zone 9

10 THE BOREHOLE ENVIRONMENT THE BOREHOLE ENVIRONMENT Zone of transition or annulus Uninvaded zone 10

11 THE BOREHOLE ENVIRONMENT (Bed Thickness) THE BOREHOLE ENVIRONMENT (Bed Thickness) Uninvaded zone Uninvaded zone 11

12 THE BOREHOLE ENVIRONMENT (Bed Thickness) THE BOREHOLE ENVIRONMENT Uninvaded zone 12

13 THE BOREHOLE ENVIRONMENT LEARNING OBJECTIVES By You the now end of can: this lesson, you will be able to: Explain mud filtrate invasion and describe the borehole environment in terms of resistivity State the resistivities in each zone within the borehole environment Discuss the distribution of fluids in a hydrocarbon reservoir List three or more types of drilling muds and identify whether their respective filtrates are low or high resistivity Explain the effect of temperature on resistivity of a NaCl saltwater solution 13

14 INVASION AND THE BOREHOLE ENVIRONMENT PART 2 ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water R w R t, R o S w 14

15 ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content R w R t, R o S w Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water R w R t, R o S w 15

16 ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content R w R t, R o S w Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water R w R t, R o S w 16

17 ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water ZONES IN AND AROUND THE BOREHOLE Zone Dimension Fluid Content R w R t, R o S w Fluid Resistivity Rock Resistivity Bed h R t Adjacent Bed Borehole d h Mud R m Mud Cake h mc R s Water Saturation Flushed d i Mud Filtrate R mf R xo S xo Uninvaded Connate Water R w R t, R o S w 17

18 INVASION OF BOREHOLE WALL Borehole wall INVASION OF BOREHOLE WALL Minimize mud filtrate invasion 18

19 INVASION OF BOREHOLE WALL Mud Cake Quality Properties of the mud Amount of overbalance (pressure) Time INVASION OF BOREHOLE WALL Tools affected: Filtrate Invasion Properties of the mud (API Fluid Loss) Time Porosity and permeability API Fluid Loss The amount of fluid (in cc) through a standard millipore filter with 100 lbs differential pressure in 30 mins 10 cc for water-based muds 4 cc for oil-based muds Resistivity Density: porosity calculation requires mud filtrate density Sonic: can be corrected using Gassmann equation 19

20 INVASION AND THE BOREHOLE ENVIRONMENT PART 3 MUD FILTRATE INVASION porosity (ϕ) = diameter of intrusion (d i ) 20

21 MUD FILTRATE INVASION porosity (ϕ) = diameter of intrusion (d i ) BASIC TYPES OF DRILLING MUD The Mud Circulating System 21

22 BASIC TYPES OF DRILLING MUD The Mud Circulating System BASIC TYPES OF DRILLING MUD Water-Based Mud (WBM) Least expensive Fresh, brackish, or sea water Type of water affects R mf Oil-Based Mud (OBM) More lubricating Made with diesel or crude oil Rarely used for environmental reasons, expense of disposal Saltwater Mud More efficient in some formations NaCl or KCl Synthetic Oil-Based Mud (SOBM) Expensive Used in deep-water drilling Uses food-quality mineral oil 22

23 BASIC TYPES OF DRILLING MUD Properties of Muds Water-based muds (WBM and saltwater) Have water filtrate Rw measured and recorded Oil-based muds (OBM and SOBM) Oil filtrate is not conductive Rm, Rmc, and Rmf are not meaningful Resistivity logging tools with electrodes will not function in OBM WELLSITE MEASUREMENT OF RMF 23

24 Resistivity Logging Tools and Interpretation Core PE TR O SK IL LS LL C RESISTIVITY OF NACI SOLUTIONS 9 pound salt water 1.08 gm/cc NaCl C O PY R IG H T RESISTIVITY OF NACI SOLUTIONS 24

25 CONVERSION TO RESISTIVITY R1 R2 = R mf = ohm.m at depth T1 R2 CONVERSION TO RESISTIVITY Arps Equation R 2 = R 1 [(T )/(T )] o F R 2 = R 1 [(T )/(T )] o C T2 235 ppm TDS 25

26 CONVERSION TO RESISTIVITY Arps Equation R 2 = R 1 [(T )/(T )] o F R 2 = R 1 [(T )/(T )] o C CONVERSION TO RESISTIVITY Arps Equation R 2 = R 1 [(T )/(T )] o F R 2 = R 1 [(T )/(T )] o C 26

27 CONVERSION TO RESISTIVITY Arps Equation R 2 = R 1 [(T )/(T )] o F R 2 = R 1 [(T )/(T )] o C ALPHABET SOUP RESISTIVITIES Water-Based Mud and Formation Fluid R m R mf R mc Resistivity of the drilling mud (qualitative indicator of mud type) Resistivity of the drilling mud filtrate (key parameter) Resistivity of the drilling mud cake (seldom needed) R w Resistivity of the formation water (key parameter) Formation R xo R t R o Resistivity of area flushed by mud filtrate (Flushed Zone) Resistivity of the uninvaded formation (no saturating fluid) Resistivity of the uninvaded formation with 100% water saturation 27

28 ALPHABET SOUP SATURATIONS S xo S w S wi S wirr S o S g ROS S or Water saturation in the Flushed Zone (often mud filtrate saturation) Water saturation in the Uninvaded Zone Initial water saturation Irreducible water saturation Oil saturation in Uninvaded Zone (S o = 1 S w if no gas is present) Gas saturation in Uninvaded Zone (S g = 1 S w in a gas reservoir) Remaining oil saturation Residual oil saturation after water-flood ALPHABET SOUP ARCHIE RELATIONSHIPS Archie I F = R o /R w = formation factor Archie IIF = 1/Φm = formation factor in terms of porosity Φ = porosity m = cementation exponent I = R Archie III R t /R o = resistivity index S w = (1/I) (1/n) = water saturation in terms of resistivity index n = saturation exponent S w = [(R w )/(f m x R t )] 1/n = water saturation (resistivity & porosity) 28

29 FACTORS AFFECTING RESISTIVITY TOOLS Shoulder bed R s Undisturbed Zone R t Shoulder bed R s Flushed (Invaded) Zone R xo Goal of Resistivity Logging LEARNING OBJECTIVES Mud R m You By the should end of this now lesson, be able you will to: be able to: Formation Resistivity Measuring Device Shoulder bed R s Flushed (Invaded) Zone R xo Undisturbed Zone R t Goal of Resistivity Logging Shoulder bed R s Explain mud filtrate invasion and describe the borehole environment in terms of resistivity State the resistivities in each zone within the borehole environment Discuss the distribution of fluids in a hydrocarbon reservoir List three or more types of drilling muds and identify whether their respective filtrates are low or high resistivity Explain the effect of temperature on resistivity of a NaCl saltwater solution 29