Basin Modeling and Petroleum System Analysis for the Aim of Minimizing Exploration Risks

N.V. Lopatin¹, N.A. Malyshev², N.N. Kosenkova², and T.P. Emets^1
1VNIIgeosystem, Moscow, Russia
²OAO “NC-“Rosneft”, Moscow, Russia

Basin Modeling in combination with Petroleum System analysis can be identify of the attractive traps, which need to be extensively explored for oil and gas using their location within the geographic extent of the system. This study offer the Basin and petroleum systems analyses for the intracratonic West Siberian Basin (WSB): 1) Upper Jurassic Bazhenov Formation as a classic very rich oil-prone marine black shale unit with a favorable basin evolution histories for HC generation, expulsion and secondary migration to the Neocomian marine sandstone reservoirs (more than 85 % of commercial oil reserves in WSB); 2) “Togur-Paleozoic petroleum system” with Early Toarcian lacustine source rocks (SR) and two different types of reservoirs: fracturing Paleozoic metamorphic rocks and coarse-grain sandstones of Early Jurassic, and 3) the principal source of gas for supergiant gas accumulations in Northern West Siberian subbasin – Albian and Upper Aptian “Pokur gas and gas-condensate system” with kerogen type III.
GALO software (Lopatin, Galushkin, Makhous, 1996, 1997, 2001) simulates the burial and thermal histories of a source rock. The programme permits multiple scenarios to be run for the palaeothermal history and maturity of kerogen, assesses the timing of oil charge from the source kitchen, and models favorable migration and accumulation geometries. This Basin modeling procedure was applied to the main zones of oil and gas accumulations of the Basin. In terms of chemical kinetics, kerogen from the Bazhenov Formation has a typical apparent activation energy (Ea) spectrum, and has an initial petroleum generative potential of 627 mg HC/g TOC. About 90 % of oil generation is genetically connected to chemical reactions with Ea=50 and 52 kcal/mol. From the beginning of the Late Cretaceous (about 90 Ma) when the Bazhenov Formation entered the “oil window” to the present-day, the intensity of oil generation was up to 420 mg HC/g TOC.
Thus while the Bazhenov Formation has a general (regional) thermal maturity of about Ro 0.62-0.87 %, the thermal maturity can locally increase in active fault zones to 1.1% Ro. Overpressure is corresponding effect on HC generation-expulsion and typical for pod of active Bazhenov SR, migration-drainage fairways and some accumulation zones. We used additional programme of numerical modeling of the pressure history for the prediction of abnormal pressure locations the Bazhenov-Neocomian petroleum system (for example, prediction abnormal Pr for the new production reservoir, J2, in Khalmerpayta w. # 2099 was 2.05, after drilling – 2.03 and so on).
The conception of petroleum system (PS) play combine the principal information about source rocks, traps, reservoirs, seals, petroleum migration pathway from source to trap, and processes, which create theirs in geological time and space. Our version of PS play can be organize in three stages. The first (1D-stage) are identification of the dominant source rocks on the basin, their petroleum potential, maturity, and 1D Basin modeling for the petroleum generation and expulsion, The second stage are the geographic extent of the P.S. and 2D-mapping a pod of active source rock, migration-drainage pathways and traps location using by 2D-seismic, logs and P.S. event chart. On this stage, principally possible to determine the geochemical prerequisites for exploration. The third stage, possible verify the 3D-choice of exploration activities on the base of quantitative estimation of migration loses, mass balance, accumulation style, and preservation degree. From here we can receive the information about exploration strategies, potential petroleum reserves and the efficiency of dominant petroleum system.
Using Basin Mod and PS technologies for the exploration risks analysis of the Bazhenov “in situ” oil accumulations has shown that the risk of drilling a dry hole following from conventional exploration strategy is 0.84, and the probability of discovering an oil accumulation is 0.1. However, if generation-accumulation history, fault and fracture architecture is know from Basin Mod and 3D-siesmic, these probabilities would be closer to 0.32 and 0.35, respectively.

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands