Abstract: Maturity modeling of the Upper Jurassic source rocks of West Siberia Basin using Amoco's FINESSE program and Global Heat Flow database

NIE, SHANGYOU, BRUCE FALKENSTEIN, VLADIMIR VYSSOTSKI, EKATERINA CASEY, ROGER MARZI and PETER KAUFMAN

The Upper Jurassic rich bituminous shale facies is the most important source rock for the entire West Siberia basin. Differences in subsidence/sediment supply resulted in the formation of an asymmetric sedimentary basin with the depocenter in the west. The two principal facies of the organic-rich bituminous shale are the Mulym'in and Bazhenov/Tutleim facies. The Mulym'in represents the distal facies of the Kimmeridgian-Early Hauterivian transgression (the western slope of the basin), and the Bazhenov/Tutleim is the distal, condensed section of the Volgian-Barremian westwardly prograding depositional system (90% of the bituminous area). The latter becomes progressively younger from east to west. The source rock thickness varies from 10 - 85 meters and TOC from 4 - 19%. This world class source rock occurs throughout the West Siberia basin in an area of ~1.1 million km². Its burial depth generally decreases southward from greater than 4000m in the north to 1000-3500m in the south. In addition to being a source rock, it is also locally a reservoir unit (Salym, Krasnolenin oil fields).

Despite the rich source rock and good reservoir properties, some of the traps are not fully hydrocarbon charged. To address this issue, basin modeling of the Bazhenov/Tutleim formations was conducted combining 1-D modeling and Amoco's proprietary software FINESSE map view modeling package. The 1-D modeling provided the basic constraint on the subsidence history and heat flow. The models are calibrated using bottom hole temperature and regional vitrinite reflectance data. These parameters are then used for the FINESSE modeling which relied on 7 regional depth maps that captured the essence of the subsidence history of the Bazhenov/Tutleim source rocks. Two FINESSE runs were generated, one using a uniform heat flow and temperature gradient constrained by the 1-D modeling, and the other using spacially variable regional heat flow map. The regional heat flow map is constructed based on 729 heat flow data points in the study area from Amoco's proprietary Global Heat Flow database. Overall, model results show excellent agreement with calibration data, with the heat flow values determined from the 1-D modeling being about 10% higher than the present heat flow values. Implications of the maturity modeling to the hydrocarbon potential of the Bazhenov/Tutleim source rocks will be addressed.