Evaluation of the Late Cretaceous-Cenozoic uplift and 1D petroleum systems modeling of the eastern Barents Sea Peter Sobolev 1 , Nikolay Sobolev 1 , Bernhard Cramer 2 , Viktor Vasiliev 1 , Evgeniy Petrov 1 1 A.P. Karpinsky Russian Geological Research Institute (VSEGEI), Russia 2 Federal Institute for Geosciences and Natural Resources (BGR), Germany
The Russia Barents Sea – achievements and problems + One of the most promising shelf area in Russia – there are 11 large oil and gas deposits; + Plans to start an industrial development for several fields in the nearest future; + The area is studied beginning from 1970-s; - The area covered with surveys and wells very irregularly; - All gas and oil fields related with Jurassic and Triassic complexes, whereas for the Timan almost whole section is productive (from Ordovician up to Triassic). - Large volume of data (especially on well logs) is not processed with modern methods.
Very irregular representability – both in plan and in cross-section. Usually only gas and oil pays are studied in some details;
Very rare sampling:
Up to 3-4 coring sections about of 5-15 m length per well with bottom about of 3000-4000 m;
Poor laboratory investigations of cores;
Low quality of geophysical logging data for many wells (digitizing errors, part of the whole section, variety of methods and devices etc.);
Absence of the reliable interpretation of geophysical logging for the most of wells.
Well log interpretation – 10 wells gamma sonic, polarization , resistivity clay volume porosity ; lithology Porosity trendlines for different rock types Main unsolved problem – there isn’t a “calibration” curve with normal porosity trend Porosity vs. depth trend
Petrophysical analysis for 10 wells Travel time ( s/ft ) – depth ( m ) Porosity – depth ( m )
Rough evaluation of regional uplift 400 - 700 м 700 - 100 0 м > 1000 м Isolines - seismic horizon “ Г ” – lower Cretaceous upper boundary 3
Examples from the literature. (Jankowsky,1962; Magara,1976). Magara(1976,1986) showed, that the acoustic interval transit time ( Δ t) of shales decreases exponentially with depth ( normal compaction trend ). Magara’s sonic log extrapolation technique 3
The main task – careful selection of data (Stokmanovskaya-1 well)
“ Gamma-ray filtration”. Only points with GR > 100 API units were chosen for the next step (these values are typical for shales).
Values with the lowest values of Δ t were taken to evaluate upper limit of uplift.
Conclusion: Upper limit of Cenozoic erosion is about of 500 m Uncompacted shale value of approximately 200 s/ft (656 s/m) 3
Vitrinite reflectance measurements Conclusion: Uplift evaluation is about of 500 m near-surface reflectance value is of 0.25% 3
Timing of regional uplift Cavanagh et al., 2006 Southwestern Barents Sea 33.9 – 2 Ma Pg3-N1 3
D 2-3 P-T J 2 K 1 P-T Thermal history - subsidence curve analysis K 1 K 1 4
Main rift events in the Barents Sea Basin (from the analysis of subsidence rate) Heat flow changing during rifting – McKenzie model 4 Time, Ma Epoch β Abun-dance Occurences in neighbouring areas 115-125 K1 < 1.2 local Normal faulting and subsidence in the Western Barents Sea 160-170 J2 < 1.2 regional Rifting over major parts of the North Atlantic 240-260 P-T ~ 2 global Global boundary. Mass extinction, rifting, basaltic magmatism, beginning of Pangaea break-up 360-380 D2-3 < 1.2 regional Rifting and magmatism throughout the Russian Platform
Generation of the today´s petroleum pools begun in Mezosoic (mainly Triassic) and ceased with the uplift´s beginning (Cenozoic) in the central parts of the Russian Barents Sea Basin;
Gas pools of Lower Triassic are very likely indigenous;
Petroleum generation in the Jurassic sequence are unlikely (though there are black shales with high organic content). However, it is possible to suggest “oil window” in the Jurassic layers for more submerged depressions;
Oil/gas in Paleozoic rocks were “cooked out” until Triassic for the Central Part of the Barents Sea. Than they might be imported into the areas with less subsidence;
For the marginal parts of the Barents Sea with reduced thickness of Mesozoic rocks a petroleum generation is possible during Mesozoic time.
Preliminary conclusions from the modeling of petroleum systems 5
„ Exploration strategy“ for the Barents Sea oil window surface Central parts of the Barents Sea Deep depressions of the Barents Sea The Pechora Sea and highs in the Barents Sea 5 Upper Jurassic Lower Triassic Devonian-Carboniferous Upper Jurassic Lower Triassic Devonian-Carboniferous Upper Jurassic Lower Triassic Devonian-Carboniferous