how many source rocks do I have? 1 Samuel Rivas, J. Grimmer, A. - PowerPoint PPT Presentation

Basin modeling at the Songkhla Basin (Gulf of Thailand) or: how many source rocks do I have? 1 Samuel Rivas, J. Grimmer, A. Alaminos, J. Navarro. Cepsa E.P., S.A. April, 5 th . 2016

Outline • Conclusions, first! • Introduction (from a regional to local perspective) • Source rocks of the Songkhla Basin (which and what are they?) • Basin modeling (featuring 1Ds, vitrinite reflectance suppression, and 3D models) • Conclusions, again! 2

Conclusions, first! • The Lower Oligocene shales are the main source rock in Songkhla. Lower Miocene shows, with the available data, much less potential. • These are oil-prone lacustrine shales with contributions of terrestrial organic material, and have a fair-to-good quality (1-5%TOC). • Vitrinite reflectance (Ro%) suppression is occurring in the basin; which means Ro% is not a good proxy for maturity. • Lower Oligocene entered the oil window as early as the Late Oligocene (23 Ma), coeval with expulsion onset, which peaked in the Mid-Late Miocene (12-5 Ma). 3

Introduction: Location Thailand 4

Introduction: Regional geological history 1. Amalgamation of crustal blocks from Devonian to Eocene times. Tectonic elements map 0 of South East Asia, at 1 present day 1 W E E 0 2 2 W 3 You are here Modified from Metcalfe, 2011. EARLY EOCENE 3 Metcalfe, 2011. 5 Modified from Doust and Sumner, 2007.

Introduction: Regional geological history 2. After the Himalayan collision, rift basins formed and filled from the Eocene to present-day. All the pre-Tertiary crust is extended, and filled with sedimentary basins Rifting is younger northward! Pre-Tertiary crust N N 6 Modified from Polachan and Sattayarak, 1991.

Introduction: the Songkhla Basin SW NE Top Mid. Miocene Top Lower Miocene Top Upper Oligocene Top Lower Oligocene Top Eocene Top Basement 2.5km 7

Source rocks of the Songkhla Basin Lower Miocene? – A proven source rock in other Gulf of Thailand basins What are the evidences? Lower Oligocene – The proven source rock for the Songkhla Basin 8

Source rocks of the Songkhla Basin: Lower Oligocene Lower Oligocene: lacustrine shales with occasional lacustrine turbiditic events. Depositional environment can be fit into the 10065 ’ tectonic setting of the basin at the moment. SW NE A A ’ Top Lower Oligocene Modified from Keighley, 2008. A A’ TOC=1-5% A A’ 10066 ’ 9 Modified from Keighley, 2008.

Source rocks of the Songkhla Basin: Lower Miocene Grey (silty) to red claystones with signs of 4253 ’ subareal exposure (siderite nodules, roots..), which correspond to flood plains. Flood plain 4254 ’ 2 km Not very promising : ( …. 10 10

Source rocks of the Songkhla Basin: TOC and HI TOC (%) 1000 0 1 2 3 4 5 6 7 Type I 3000 900 Lower Miocene 800 4000 HI (mg HC/g Organic Carbon Lower Oligocene 700 5000 600 6000 Depth (ft) 500 Above Lower Oligocene 7000 400 Lower Oligocene 300 8000 Below Lower Oligocene 200 9000 Type III 100 10000 0 0 20 40 60 80 100 120 140 160 180 200 11000 OI (mg CO2/g Organic Carbon) HIs and OIs from 9 wells, all from Lower Oligocene: mixed TOCs from 11 wells: 85% of the values belong to the Oligocene and below. Organic richness is in the Lower Type I-III signature. Palynology, paleogeography, and more Oligocene and below! geochemistry support this HI=100-900 mgHC/g OC TOC Max =5.26% 11 11

Source rocks of the Songkhla Basin: isotopes and biomarkers 7 Fluvio-deltaic Lacustrine 6 0.60 5 Carbonates 4 0.50 3 Canonical Variable (CV) 2 0.40 1 Marls H31R/Hopane 0 Marine -1 0.30 Marine shales -2 Lacustrine -3 0.20 -4 -5 -6 0.10 Calculated from δ 13 C of aromatic -7 and saturate HCs and used to -8 distinguish terrigenous from 0.00 -9 marine sources (Sofer, 1984). 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 -10 C26/C25 tricyclic terpanes 0 2 4 6 8 10 Pristane/Phytane Oil samples ( ) and rock extract ( ) analyses from 7 Oil sample analyses from 5 wells. Guess what? wells. Confirmation of the lacustrine source! More lacustrine source! 12 12

Source rocks of the Songkhla Basin: quality 1000 Lower Oligocene 900 800 700 Lower Oligocene source rock values show a HI(mg HC/g TOC) fair-to-good source rock! 600 500 Lower Miocene … insufficient data for a Very good meaningful answer, but probably a poor 400 source rock 300 Good 200 Fair 100 Poor 0 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 TOC (%) Modified from Tommeras and Mann, 2008. 13 13

Source rocks of the Songkhla Basin: mature? …there is a whole basin producing some oil, so definitely YES they are mature!!! We need to have a better understanding than that! 14 14

Basin modeling: there is something wrong with these %Ro… Well-2 Well-1 Well-3 Immature T calibrated models show a mature Lower Oligocene Temperature data source rock Mature %Ro calibrated models show a very immature Lower Oligocene source rock !!! How can that be?! Vitrinite ref. data 15 15

Basin modeling: there is something wrong these %Ro… Calculating an empirical vitrinite reflectance from Tmax (Jarvie, 2005) shows much higher %Ro values than the observed. Below, an example from the deepest Songkhla well. Equivalent vitrinite reflectance from T max Measured vitrinite reflectance Vitrinite reflectance suppression! 16 16

Basin modeling: there is something wrong these %Ro… Perhydrous vitrinites are causing vitrinite reflectance suppression at the Songkhla Basin; %Ro values are lower that what they should be. This happens in other basins around the world (Petersen, 2009, Waples, 1994), specially in tropical areas. This makes plant material (vitrinite) less H 2 O reactive to heating, thus giving lower maturities 17 17

Basin modeling: input and calibration Knowing we can only trust fully the temperature data to calibrate the models… we jump to the 3D model!. Calibration examples (with temperature data) Input N A’ A A’ A 11 Layers 12 Horizons 1 Type I source rock, TOC=2%, HI=900mgHC/gOC (no reason for a second source rock) McKenzie rift 34-10Ma 18 18 Temperature data

Basin modeling: results 1D burial plots at the Lower Oligocene depocentre Lower Oligocene present day maturity map Source rock maturity L. Oligocene Transformation Ratio L. Miocene enter the oil window at 8 Ma TR increases progressively L. Oligocene enter the oil window at 24 Ma L. Oligocene Generated Mass/Ma Depocentre Max generation occurs in Mid-Late Miocene 19 19

Basin modeling: results Expulsion from source rock layer (events) Expulsion peak 11.6-5.0 Ma Expulsion initiation 23.0 Ma Expulsion begins in Late Oligocene and peaks in Mid-Late Miocene. Expulsion from source rock layer (cumulative) 2.7 Billion barrels 20 20

Conclusions, again! • The Lower Oligocene shales are the main source rock in Songkhla. Lower Miocene shows, with the available data, much less potential. • These are oil-prone lacustrine shales with contributions of terrestrial organic material, and have a fair-to-good quality (1-5%TOC). • Vitrinite reflectance (R o %) suppression is occurring in the basin; which means R o % is not a good proxy for maturity. • Lower Oligocene entered the oil window as early as the Late Oligocene (23 Ma), coeval with expulsion onset, which peaked in the Mid-Late Miocene (12-5 Ma). The summary of our knowledge on the source rocks and maturity of the basin! 21 21

References • Doust, H., and Sumner, H. S. [2007] Petroleum systems in rift basins: A collective approach in Southeast Asian basins: Petroleum Geoscience, v. 13, p. 127 – 144. • Jarvie, D.M., Hill, R.J., Pollastro, R.M. [2005] Assessment of the Gas Potential and Yields from Shales: the Barnett Shale Model in Cardott, B.J. (ed.), Unconventional energy resources in the southern Midcontinent, 2004 symposium: Oklahoma Geological Survey Circular 110, 2005, p. 37-50. • Keighley, D. [2008] A lacustrine shoreface succession in the Albert Formation, Moncton Basin, New Brunswick: Bulletin of Canadian Petroleum Geology, v. 56, p.235-258. • Metcalfe, I. [2011] Palaeozoic – Mesozoic history of SE Asia: Geological Society Special Publication, v. 355, p. 7 – 35. • Petersen, H. I., Sherwood, N., Mathiesen, A., Fyhn, M. B. W., Dau, N. T., Russell, N., Bojesen, J. A., Nielsen, L. H. [2009] Application of integrated vitrinite reflectance and FAMM analyses for thermal maturity assessment of the northeastern Malay Basin, offshore Vietnam: Implications for petroleum prospectivity evaluation. Marine and Petroleum Geology 26, 319-332. • Sofer, Z. [1984] Stable carbon isotope compositions of crude oils: application to source depositional environments and petroleum alteration. AAPG Bulletin, 68, 31-49. • Waples, D. W. [1994] Maturity Modeling: Thermal Indicators, Hydrocarbon Generation, and Oil Cracking: Chapter 17: Part IV. Identification and Characterization. AAPG Memoir 60: The Petroleum System--From Source to Trap, 285-306. 22 22

Thanks for attending! Questions? Enjoy the event and see you next time! And feel free to contact! 23 23 samuel.rivasd@cepsa.com