FORMATION EVALUATION PETE 321

Transcription

1 FORMATION EVALUATION PETE 321 CROSSPLOTS (Porosity and Lithology) Summer 2010

2 TWO-MEASUREMENT POROSITY CROSSPLOTS Two measurements determine two unknowns Formations with one lithology Lithology Porosity Formations of two known constituents Can determine a more accurate value of porosity Can determine the percentage of each mineral Complex lithologies Can determine a more accurate value of porosity Cannot determine percentage mineral makeup

3 COMMON POROSITY CROSSPLOTS Neutron-density Sonic-neutron Sonic-density All have complicating effects Shaliness Hydrocarbons (gas) Fractures

4 NEUTRON-DENSITY CROSSPLOTS Most frequently used Developed for clean, liquid-saturated formations Boreholes filled with water or waterbased muds Several charts, depending on tools CP-1 s Schlumberger CNT-K-1 s and DSN-II-1 s Halliburton

5 NEUTRON DENSITY CROSSPLOT Axes Neutron limestone Density NE-SW Lith. Lines Sandstone Limestone Dolomite NW-SE Por. Lines Connect equal por pts Nearly parallel Bulk density (Mmg/m 3 or g/cc) Sulfur Salt 2.45 Langbeinite ~2.83 φ = 10 Polyhalite 22% φ = 20 Trona φ = Apparent neutron porosity (lspu) A B C % Ls = BC / AC % Dol = AB / AC Matrix may be: Ls and dolomite Ss and dolomite

6 CHART BASED on... POR-12/13 Neutron POR-10 Density Bulk density (Mg/m 3 or g/cc) Sulfur Salt Langbeinite Polyhalite Trona Apparent neutron porosity (lspu)

7 Parallel lith. lines Constant separation Distinct position Log presentation (next) Bulk density (Mg/m 3 or g/cc) Sulfur Salt Langbeinite Polyhalite Trona Apparent neutron porosity (lspu)

8 DENSITY-NEUTRON PRESENTATION φ=12 ls Parallel lith. lines Constant separation Distinct position Log presentation Limestone scaling Neutron 45 to -15 lspu Density 1.95 to 2.95 g/cc LS ρ and φ values overlie in Ls Other scalings possible φ=30 ls ρ b ~2.23 ρ b ~2.53 φ=12 ss ρ b =2.45; φ n = 9 φ=30 ss ρ b =2.15; φ n = 27 φ=12 dol ρ b =2.67; φ n = 15 φ=30 dol ρ b =2.33; φ n = 33

9 EXAMPLE LOG - WELL X ft Zone D 150ft Pe = 1.8-2: SS Den-Neut LS compatible Ntrn to rt of Den SS lithology Large sep. above 150 ft Shales Pe = Neutron left of Density B C OWC D

10 OTHER 1.9 EFFECTS 2.0 Sulfur Shales 2.1 Salt Trona Gas Fractures No effect, both logs respond tototal porosity Bulk density (Mg/m 3 or g/cc) Langbeinite Polyhalite Apparent neutron porosity (lspu) 40

11 EXAMPLE LOG - DN PLOT, WELL X Shale Effect Borehole effects and calcite stringers cause outliers

12 Density-Neutron Response WELL X Qtz Calcite Dolomite GR < 30 & ILD < 1 GR > 80 GR < 30 & ILD > 1 DN PLOT (EXCEL) Values do not all fall on Ss line owing to: Borehole effects Carbonate cements Shaliness HC vs water Statistical fluctuations of tools Bulk density, g/cc Oil Water Shale plots like dol; use GR to differentiate Neutron Porosity, limestone

13 GAS EFFECT - 1 WELL A Zone (depth) A A: 0-20 B: C: D: Low GR Den = 2.95 (high) Neut por. = -2 B, D high GR C D-N litho scaling 290 ft. D-N near overlay below A B C D LS Calibration Gas Effect 0

14 GAS EFFECT -2 WELL A C A B D Shale C B Marl A

15 DENSITY-NEUTRON - OTHER COMMENTS Density log may be displayed as porosity Density-Neutron overlay for water- filled lithology Curve order as with g/cc scaling Shale/Gas effects Across litho lines: Lithology most affected Along porosity lines: Porosity least affected Response lines change with tool type

16 COMMON POROSITY CROSSPLOTS Neutron-density Sonic-neutron Sonic-density

17 SONIC-NEUTRON CROSSPLOTS Developed for clean, liquidsaturated formations Boreholes filled with water or waterbase muds

18 SONIC-NEUTRON PLOTS - 1 Similar layout to density-neutron Time average Field observation Two lines - two porosity models Wylie time average Raymer-Hunt-Gard. Charts CP-2 s (S) CNT-K-2 s (H) t, Sonic transit time (μs/ft) Syivite Trona Apparent neutron porosity (lspu)

19 Shale - NE region Fracs - South Gas - NW SONIC-NEUTRON PLOTS - 2 t, Sonic transit time (μs/ft) Time average Field observation Syivite Trona Apparent neutron porosity (lspu)

20 WELL X, SN PLOT W/ GR Shaliness Optimistic porosity Lithology OK HC effect slight Sonic slowness, ms/ft Sonic-Neutron (CNL), Fresh Mud Quartz Calcite Dolomite GR < 30 GR > Neutron, apparent LS pu

21 COMMON POROSITY CROSSPLOTS Neutron-density Sonic-neutron Sonic-density Poor porosity resolution Useful for some evaporites

22 SONIC-DENSITY CROSSPLOTS Poor lithology and porosity Multiple lines Density-Sonic Response Field Lines Only Qtz Calcite Dolomite WTA RHG Useful for Evaporites Vsh Density Sonic DT

23 WELL X, DENSITY-SONIC Clean points cover all lines Shale point distinct Density-Sonic Response Qtz Calcite Dolomite GR < 30 GR > Density Sonic DT

24 MID PLOTS - 2 LOGS

25 Density-Sonic Response DENSITY- SONIC Vsh What is shale content of formation comprised of 2 minerals? Locate 100%shale and clean formation Grid to give Vsh Density Qtz Calcite Dolomite GR < 30 GR > Vsh = 0 Vsh = 1 Sonic DT

26 MID PLOTS PRINCIPLES 1. DETERMINE APPARENT MATRIX DENSITY Lith. lines 3 of many poss. Each line diff. lith. Line definition Use endpoint loc n Value of ρ b for φ = 0 Bulk density (Mg/m 3 or g/cc) ρ b = 2.30, φ n = ρ maa= 2.68 Called ρ maa Example Logs show ρ b = 2.30, φ n = 21 ρ maa = Apparent neutron porosity (lspu)

27 MID PLOTS PRINCIPLES Lithology Lines Similar to D-N Line Definition Use endpoint loc n Value of Δt for φ = 0 Called Δt maa Example Logs show Δt = 78, φ n = DETERMINE APPARENT MATRIX TRANSIT TIME 110 t, Sonic transit time (μs/ft) Syivite Field observation Δt maa = 53 Δt = 78, φ n = 21 Trona Δt maa = Apparent neutron porosity (lspu)

28 THREE - MEASUREMENT CROSSPLOTS For lithology determination only Used when 3 porosity logs available Three types Density-Neutron-Sonic (M-N plot) Density-Neutron-Sonic (MID plot) Density-Neutron-Pe (U maa -- ρ maa plot)

29 3. DETERMINE LITHOLOGY MID PLOTS PRINCIPLES 3 Lithology Points Example ρ maa = 2.68 Δt maa = 53 Results 50% quartz 50% calcite Ρ maa Calcite Dolomite Quartz Δt maa

30 Calculating Δt maa and ρ maa At each depth: Δt, ρ b, and φ n 1. Obtain φ DN and φ SN from crossplots 2. ρ maa = (ρ b φ DN ρ fl )/(1 - φ DN ) 3. Δt maa = Δt (φ SN Δt)/ factor may vary somewhat

31 SUMMARY 3 types of porosity logs Density, Neutron, Sonic These logs respond differently to matrix, fluids and pore types Use for 2-log crossplots Crossplots allow determination of porosity and proportions of 2 minerals, if mineralogy is known Neutron density is most commonly used crossplot

32 SUMMARY 3-Log Crossplots Lithology only Several versions MID plot MN plot U maa -- ρ maa plot