PVT Concepts (Reservoir Fluids)

Transcription

1 PVT Concepts (Reservoir Fluids) Thomas A. Blasingame, Ph.D., P.E. Department of Petroleum Engineering Texas A&M University College Station, TX (USA) Orientation Phase Behavior Slide 1

2 PVT Concepts (Reservoir Fluids) Self-Evaluation: PVT Concepts 1.Reservoir Fluids: "Black Oil" (p>p b ): B o, μ o, c o are ASSUMED constant "Solution-Gas Drive" (all p): B o, μ o, c o = f(p) "Dry Gas" (p>p d ): B g, μ g, c g = f(p) 2.Diffusivity Equations: "Black Oil" case. "Solution-Gas Drive" case. "Dry Gas" case. Orientation Phase Behavior Slide 2

3 PVT Concepts (Reservoir Fluids) Reservoir Fluids: Schematic Phase Diagrams Generic (single and multi-component cases) Black Oil Solution-Gas Drive Dry Gas "Black Oil" (p>p b ) Properties: B o, μ o, c o (ASSUMED constant) "Solution-Gas Drive" (all p) Properties: B o, μ o, c o "Dry Gas" (p>p d ) Properties: B g, μ g, c g Summary of Fluid Properties and Sources Orientation Phase Behavior Slide 3

4 Schematic Diagram for a Single Component System From: Properties of Petroleum Reservoir Fluids Bursik (1957). Schematic p-t Diagram: Single Component System Note the "Liquid+Vapor" line. Single component systems not of interest, other than for illustration. Orientation Phase Behavior Slide 4

5 Generic Schematic Diagram for a Multi-Component System From: Fundamentals of Reservoir Engineering Calhoun (1953). Schematic p-t Diagram: Multi-Component (Hydrocarbon) System Note the "Bubble Point" and "Dew Point" lines. Location of critical point determines fluid type. Orientation Phase Behavior Slide 5

6 Generic Schematic Diagram for Hydrocarbon Reservoir Fluids From: Fundamentals of Reservoir Engineering Calhoun (1953). (modified to reflect various reservoir fluid cases) Schematic p-t Diagram: Hydrocarbon Reservoir Fluids Names represent conventional nomenclature. Locations of names represent relative locations of these fluid types. Orientation Phase Behavior Slide 6

7 Black Oil p-t Diagram From: Properties of Petroleum Fluids McCain (1990). Schematic p-t Diagram: Black Oil Fluid is typically dark black, brown, or dark green. γ o >40 o API, (GOR) i < 2000 scf/stb, B oi < 2.0 RB/STB, C 7+ > 20 %. Orientation Phase Behavior Slide 7

8 Volatile Oil p-t Diagram From: Properties of Petroleum Fluids McCain (1990). Schematic p-t Diagram: Volatile Oil Fluid is typically dark brown, orange or green. γ o <45 o API, 2000 < (GOR) i < 3300 scf/stb, B oi > 2.0 RB/STB, 12.5 < C 7+ < 20 %. Orientation Phase Behavior Slide 8

9 Retrograde Gas p-t Diagram From: Properties of Petroleum Fluids McCain (1990). Schematic p-t Diagram: Retrograde Gas Fluid is typically light brown, orange, green, or water-white. 45<γ o <60 o API, 3300 < (GOR) i < 150,000 scf/stb, C 7+ < 12.5 %. Orientation Phase Behavior Slide 9

10 Wet Gas p-t Diagram From: Properties of Petroleum Fluids McCain (1990). Schematic p-t Diagram: Wet Gas Fluid is typically very light water-white. (GOR) i > 50,000 scf/stb. Orientation Phase Behavior Slide 10

11 Dry Gas p-t Diagram From: Properties of Petroleum Fluids McCain (1990). Schematic p-t Diagram: Dry Gas No fluid is produced at surface or in the reservoir. Orientation Phase Behavior Slide 11

12 "Black Oil" Fluid Properties (Various) "Black Oil" PVT Properties: (general behavior, p b =5000 psia) Note the dramatic influence in properties at the bubblepoint pressure. The oil compressibility is the most affected variable (keep this in mind). Orientation Phase Behavior Slide 12

13 "Solution-Gas Drive" Properties (1/(μ o B o ) for p<p b ) "Solution-Gas Drive" PVT Properties: (1/(μ o B o ), p<p b, p b =5000 psia) Attempt to illustrate that 1/(μ o B o ) constant for p<p b. This would allow us to approximate behavior using "liquid" equations. Orientation Phase Behavior Slide 13

14 "Solution-Gas Drive" Properties (μ o c o for p<p b ) "Solution-Gas Drive" PVT Properties: (μ o c o, p<p b, p b =5000 psia) Attempt to illustrate that μ o c o is NEVER constant. CAN NOT approximate behavior using "liquid" equations (or so it seems). Orientation Phase Behavior Slide 14

15 "Dry Gas" μ g z vs. p "Dry Gas" PVT Properties: (μ g z vs. p) Basis for the "pressure-squared" approximation (i.e., use of p 2 variable). Concept: (μ g z) = constant, valid only for p<2000 psia. Orientation Phase Behavior Slide 15

16 "Dry Gas" p/(μ g z) vs. p "Dry Gas" PVT Properties: (p/(μ g z) vs. p) Basis for the "pressure" approximation (i.e., use of p variable). Concept: (p/μ g z) = constant (never valid). Orientation Phase Behavior Slide 16

17 "Dry Gas" μ g c g vs. p "Dry Gas" PVT Properties: (μ g c g vs. p) Concept: If μ g c g constant, pseudotime NOT required. Readily observe that μ g c g is NEVER constant, pseudotime required. Orientation Phase Behavior Slide 17

18 Summary: Formation Volume Factor Formation Volume Factor: B o,g,w Fluid volume at reservoir conditions B o,g,w = Fluid volume at standard conditions B o,g,w is defined as a volume conversion for oil, gas, or water and is defined on a mass (or density) basis. The Formation Volume Factor "converts" surface volumes to downhole conditions. Typical values: Oil: 1.2 to 2.4 RB/STB Gas: to 0.01 rcf/scf Orientation Phase Behavior Slide 18

19 Summary: Fluid Viscosity Viscosity: μ o,g,w Is a measure of a fluid's internal resistance to flow... the proportionality of shear rate to shear stress, a sort of internal friction. Fluid viscosity depends on pressure, temperature, and fluid composition. Typical values: Oil: 0.2 to 30 cp Gas: 0.01 to 0.05 cp Water: 0.5 to 1.05 cp Orientation Phase Behavior Slide 19

20 Summary: Fluid Compressibility Fluid Compressibility: c o,g,w c 1 = B db dp o o + o B B g o dr dp Typical values: Oil: 5 to 20 x10-6 psi -1 (p>p b ) 30 to 200 x10-6 psi -1 (p<p b ) Gas: 50 to 1000x10-6 psi -1 Water: 3 to 5 x10-6 psi -1 Formation Compressibility: c f 1 dφ c f = φ dp Typical values: Normal: 2 to 10 x10-6 psi -1 Abnormal: 10 to 100 x10-6 psi -1 so c g 1 = B g db g dp c 1 = B db dp w w + w B B g w dr dp sw Orientation Phase Behavior Slide 20

21 Summary: Oil PVT Correlations Oil PVT Correlations R s /p b B o μ o c o Standing Lasater Vasquez and Beggs Glaso Lasater- Standing Petrosky and Farshad Beggs and Robinson Beal ( generally used as default) Orientation Phase Behavior Slide 21

22 Summary: Gas PVT Correlations Gas PVT Correlations z-factor μ g Dranchuk, et al. Beggs and Brill Hall and Yarborough Lee, et al. Carr, et al. ( generally used as default) Gas compressibility (c g ) is computed from the z-factor using: c g 1 = B g db g dp 1 1 p z Orientation Phase Behavior Slide 22 = dz dp

23 PVT Concepts (Reservoir Fluids) End of Module Thomas A. Blasingame, Ph.D., P.E. Department of Petroleum Engineering Texas A&M University College Station, TX (USA) Orientation Phase Behavior Slide 23