Estimation and destination of some of the eroded Post Mid-Miocene sediments using a classic method- Vitrinite Reflectance (VR). 28TH of February, 2013
Presentation Outline • Why do this study? • What is Vitrinite Reflectance? • Location of wells • VR – depth plots • VR – temperature plots • Summary
Convergent margin phase: encroachment of Caribbean plate Passive margin phase Why this study? Unconformities. (Higgs. 1997) • Where is the missing sediment and can it be potential reservoirs?
What is a Maceral? MACERAL (from Latin: “macerare”, to soften) Stopes, 1935 • “Macerals are constituentsofcoals, occurring naturally in the sedimentary, metamorphic, and igneous materials of the earth” Spackman, (1958)
What is Vitrinite Reflectance- VR • Vitrinite Reflectance (%Ro) is a measurement of the • percentage of light reflected off the vitrinite maceral at • oil immersion • Vitrinite reflectance Ro as a thermal indicator • Thermodynamic record are preserved in rock and such records are irreversible. • Increase in burial causes progressive increase in temperature; thus maturity increases with depth.
VRvs Depth plots . Moolenaar , 1996 • Note the lg scale on the x axis • Can be used to estimate eroded sediment , Dow (1977) 1400 m
Erosion estimation based on Dow (1977) ; using 0.2 as a near surface VR estimate Dow (1977) The 0.2 estimate has limitations 1) No significant unconformities 2) Heating rate of 1- 10 degrees C/ Myrs (no igneous intrusions 3) No large variations in the geothermal gradient 4) Depends on whether or not the studied section is in Tropical or Temperate climate. 5) Indicates the depth of diagenesis
VR values used in thermal history reconstruction • VRo valued tied to a maximum palaeo-temperature • Indicates the oil window for Type 1 and Type 2 kerogens
Maximum PalaeotemperaturevsVR values Saxony Basin, Germany North Sea Kearl Lake, Alberta Santos Basin, Brasil Mahakam Delta, Indonesia Gulf Of Mexico
Well locations Well D Well C Well E Well B Well A
Ro from Well A with an estimated 4552’ to 1300’ of missing sediment. 0.5 Early Pliocene Miocene Depth (ft) Missing Late Pliocene to E. Pleistocene, Early Miocene and Palaeocene Oligocene Eocene Cretaceous L. Cretaceous source rock is in the main oil window
Difference between the maximum palaeotemperature and the present day temperature- Well A Average difference in temperatures is 21C
Ro from Well B with an estimated 5851’ to 2956’ of missing sediment? Late Miocene to Early Pliocene 0.5 Early Miocene to Oligocene Missing Late Pliocene to E. Pleistocene, Early Miocene Missing Mid-Miocene and Late Pliocene-Present sediment Oligocene to Cretaceous Depth (ft) Cretaceous L. Cretaceous source rock is in the main oil window
Difference between the maximum palaeotemperature and the present day temperature- Well B Average difference in temperatures is 38C
Ro from Well C with an estimated 4970’ to 2689’ of missing sediment?. 0.5 Late Pliocene to Pleistocene Early-Miocene Missing Mid to Late Miocene Depth (ft) Oligocene Eocene
Difference between the maximum palaeotemperature and the present day temperature- Well C Average difference in temperatures is 50C
Ro from Well D with an estimated 6000’ of missing sediment. 0.5 Pleistocene Pliocene Missing the Late Cretaceous to Mid Miocene Depth (ft) Late Miocene Any possible L. Cretaceous source rock maybe in the oil to gas phase Early Cretaceous Y= -10854ln(x)-9148
Difference between the maximum palaeotemperature and the present day temperature- Well D Average Pre Miocene difference in temperatures is 57
Well locations Well D Well C Well E Well B Well A
Ro from Well E with an estimated 300’ to 2740’ of extra sediment 0.5 Sediment reached approximately 92 C Late Pliocene to Early Pleistocene? Approximately 5,000’ of reworked or recycled vitrinite. Possible MLE equivalent Uplift has to be quick in E.Pleistocene The VR data was backed up with pore maturity data LatePliocene Vitrinite in deep water Y= -13881(lnx)-24272
Difference between the maximum palaeotemperature and the present day temperature- Well E Average Late Pliocene difference in temperatures is 1
Top Cretaceous , Gibson et al. 2005 • Pleistocene • Southern Range transpressional uplift at about 1.6 Ma – regional Southern Anticline • Inversion of Caroni Basin Onshore Cretaceous is at 4000’ to 6000’.
Where is the reworked sediment coming from? Seismic indicates a strong NE-SW bias Well D Well C Well E Well B Well A
Advantages of Vitrinite Reflectance (Ro) • Irreversible • Insensitive to rock composition • Covers wide temperature range • Present in most sedimentary rocks (Silurian to present)
Issues with VRo: Sample Preparation Affects Vitrinite Reflectance Values
Vitrinite Reflectance of Ditch Cuttings Has Pitfalls Effect on Ro • Caving Lower • Rough vitrinite Lower • Suppression Lower • Mud contamination Usually Lower • Oxidized vitrinite Usually Higher • Recycled/reworked Higher • Incorrect maceral identification Both • Statistical errors (few measurements) Both
Summary • Vitrinite is a coal maceral derived from wood. • Vitrinite reflectance cannot tell you whether or not a rock • generated oil or gas • It may be difficult to accurately estimate the amount of missing sediment due to differences in thermal gradients and thermal conductivities of the sediment. • The deep water area has some definitive reworked sediment (the origin and final site of deposition is difficult to determine) Are there potential MLE equivalent reservoirs in the deep water? • There exists different maturities for sediment of the same age onshore Trinidad. • Can reworked sediment be reservoirs for the deep water area?
Structural Domains , Trinidad and Tobago Trinidad and Tobago Asset