THERMAL MATURITY OF SOURCE ROCKS AND CONTROLS TO OIL QUALITY IN THE EAGLE FORD SHALE, TEXAS

Transcription

1 THERMAL MATURITY OF SOURCE ROCKS AND CONTROLS TO OIL QUALITY IN THE EAGLE FORD SHALE, TEXAS Xun Sun, Tongwei Zhang and Daniel Enriquez B ureau of E conom ic G eology

2 THERMAL MATURITY Suitable thermal maturity measurement for Eagle Ford shale CONTROLS TO OIL QUALITY Evaluate the amount and mobility of retained oil, define thermal maturity ranges of high quality oil for the Eagle Ford shale

3 Well locations Compare multiple thermal maturity parameters Tmax Iona Biomarker thermal maturity parameters MPI-1 (aromatic compounds) Characterize retained oil geochemical characteristics CH Zavala C4 A3 M K1&K2 Total amount of retained oil Mobility of retained oil, and maturity range Modified from Hammes et al. (2016).

4 Dominant kerogen types in Eagle Ford Formation 1) H/C vs. O/C plot 2) S/C vs. O/C plot

5 H/C atomic ratio Type II Kerogen is Dominated in Van Krevelen Diagram mean evolution path of Type I mean evolution path of Type II Shanklin W R Hendershot Brechtel Blumberg Halff Getty, Hurt Shell, Leppard 0.5 mean evolution path of Type III O/C atomic ratio

6 S/C 100 atomic ratio High-sulfur and Medium-sulfur Kerogens In Lower Eagle Ford Formation Blumberg Hendershot 8.0 Shanklin W R Hendershot Iona Brechtel 6.0 high-sulfur kerogens S/C 0.04 to 0.08 Type II-S Blumberg Brechtel Halff 4.0 Getty, Hurt Medium-sulfur kerogens S/C 0.02 to 0.04 Shell, Leppard 2.0 Menilite Type-IIS kerogen 0.0 Low-sulfur kerogens S/C < 0.02 to Monterey type IIS kerogen Upper Iona Lower Iona O/C atomic ratio Orr, 1986

7 Hydrogen index (mghc/g TOC) Hydrogen index (mghc/g TOC) Marine Type II kerogen, maturity ranges from immature to oil cracking to gas stage 900 I Iona 900 II I 0.5% Ro Iona 750 CH 750 CH II low OI is substitution of sulfur for oxygen in the kerogen Zavala M K1 K2 A Zavala M K1 K2 A3 300 C4 300 Immature Zone Oil Zone C III 1.3% Ro III Gas Zone Oxygen index (mg HC/g TOC) Tmax ( C)

8 Pristane/nC17 Marine Type II kerogen in reducing condition Samples from eight wells represent maturity increasing trend UEF Iona LEF Iona CH Zavala M K1 K2 A3 C Phytane/nC18

9 SARA Fractions in Extracted OM Maturity increasing Retained oil mobility increases with maturity A3, C4 content more heavy fractions (NSO+Asph) Eagle Ford produced oil

10 THERMAL MATURITY Multiple thermal maturity parameters comparison Tmax Biomarker thermal maturity parameters MPI-1 (aromatic compounds)

11 T max can be interfered from indigenous bitumen in immature rocks and mineral matrix in high-mature rocks indigenous bitumen high-mature S2 (modified from Hart et al. 2015)

12 Terpanes Steranes C29αββ/(ααα+αββ) C29αααS/(S+R) C35 22S/(22S+22R) C29Ts/(C29Ts+C29H) Ts/(Ts+Tm) Biomarker maturation parameters respond in different ranges of maturity Estimate the maturity relative to the oil window affected by mineralogical composition and S content (Peters et al. 2005)

13 Depth (m) Biomarker thermal maturity parameters for LEF Iona show inconsistency in LEF due to high S content The Ts /Tm (tricyclic terpanes) C29Ts/(Ts+H), and C29α/(α+β) ratios are not affected by sulfurization and are suitable for thermal maturity assessment for Eagle Ford immature rocks C29Ts/(C29Ts+C29H) Ts/(Ts+Tm) C29αββ/(ααα+αββ) percentage(%) percentage(%) UEF Iona UEF Iona UEF Iona UEF Iona C29αααS/(S+R) UEF Iona 22S/(22S+22R)C35% 70 LEF Iona LEF Iona LEF Iona LEF Iona C29αααS/(S+R) UEF Iona 22S/(22S+22R)C35%

14 S content DBT/P Low maturity well Iona and CH have high S content sulfate-rich marine carbonate UEF Iona LEF Iona CH Zavala M K1 1.5 K2 A3 C sulfate-poor Marine sulfate-poor fluvial deltaic Pr/Ph reducing (lines and field are modified from Hughes et al., 1995)

15 Maturity increasing %Ro Tmax The Ts/(Ts+Tm) ratio is suitable for thermal maturity assessment below the peak oil generation stage Iona CH Zavala Ts/(Ts+Tm) biomarker thermal maturity parameter shows lower standard deviation than Tmax for low maturity samples from Iona and CH Ts/(Ts+Tm) Maturity increasing

16 (Peters et al. 2005) MPI-1 (aromatics) thermal maturity parameter is applicable for mature and over mature measurement Me MPI-1 = (1.5{[2-MP]+[3-MP]})/(P+[1-MP]+[9-MP]) (Radke et al, 1988)

17 Maturity increasing %Rc MP1 MPI-1 thermal maturity parameter overestimates maturity of Iona and CH Inaccurate for low maturity measurement Iona CH Zavala Ts/(Ts+Tm) Maturity increasing

18 %Rc MP1 %Rc MP1 shows lower standard deviation than %Ro Tmax for samples from M, K1, K2 and C4, and it is applicable for high maturity measurement (%Ro > 0.9) Iona CH Zavala M K1 K2 A3 C %Ro Tmax

19 CONTROLS TO OIL QUALITY Evaluate the amount of retained oil Mobility of retained oil Define thermal maturity ranges of high quality oil for the Eagle Ford shale

20 S1/TOC (mg /g) 400 Free oil content (S1) is high (S1/TOC > 100mg/g) for most of the samples except Iona and C4 %Ro Tmax High free oil Iona CH 200 Zavala M S1/TOC = 100 K1 K2 A3 C %Ro Tmax

21 S1/TOC (mg/g) Free oil content (S1) is high (S1/TOC > 100mg/g) for samples maturity range 0.8 ~ 1.30 %Ro MP1 Iona CH 300 Zavala Mauch 250 K1 High free oil 200 K2 A3 150 C4 100 S1/TOC = %Rc MP1

22 EOM/ROCK (mg/g) The significant amount extractable organic matter zone (EOM > 5mg/g rock) is present throughout the oil window (0.8 to 1.2 %Ro) significant amount of extractable oil zone Variations within well scale Iona CH Zavala M K1 K2 A3 C %RC MP1

23 EOM/TOC (mg/g) The significant amount extractable organic matter zone (EOM > 200mg/g TOC) is present throughout the oil window (0.8 to 1.2 %Ro) significant amount of extractable oil zone Iona CH Zavala M K1 K2 A3 C %Rc MP1

24 SAT+ARO/NSO+ASPH The mobility parameter, SAT+ARO/NSO+ASPH defined the best quality oil, the maturity range from 1.07 to 1.20 %Ro (MPI-1 calculated) for the Eagle Ford Shale Moblity parameter: SAT+ARO/NSO+Asph ratio = saturated + aromatics polar compund+aspaltene Iona CH Zavala M K1 K2 A3 C4 most producible oil zone %Rc MP1

25 SAT+ARO/NSO+ASPH EOM/TOC (mg/g) significant amount of extractable oil zone Iona CH Zavala M K1 K2 A3 C Iona CH Zavala M K1 K2 A3 C4 Best oil quality and quantity zone in Eagle Ford Maturity range from 1.07 to 1.20 %Ro (MPI-1 calculated) %Rc MP1

26 CONCLUSION Multiple thermal maturity parameters (Tmax from Rock-Eval pyrolysis, biomarkers thermal maturity parameters and MP1 from aromatics) were compared. The Ts /Tm (tricyclic terpanes) ratio is suitable for thermal maturity assessment for Eagle Ford shale that are below the peak oil generation stage. The methylphenanthrene index (MPI-1) is reliable for thermal maturity assessment for mature to gas condensate stage rocks. Both oil quality and quantity in the Eagle Ford shale are controlled by the thermal maturity. The mobility parameter, SAT+ARO/NSO+ASPH and %Ro (MPI-1) defines the most favorable thermal maturity range (1.07 to 1.20 %Ro) for shale oil exploration in the Eagle Ford shale based on the data in this study.