Relative Contributions of Geological Factors to Uncertainty of Hydrocarbon Expulsion from the Qingshahou Source Rock in the North Shongliao Basin, China

Abstract

Hydrocarbon expulsion from a source rock is the basis of resource assessment of oil and gas. Model results for hydrocarbon expulsion from a source rock are dependent on the geomathematical models used, selected calculation parameters and available geological data; the sensitivity and uncertainty of the assessments are of greater and greater concern. This paper, applying basin modelling and uncertainty analysis methods to the SHONGLIAO basin, studied the effects and relative contributions of thirteen major geological factors to the uncertainty of model results for hydrocarbon expulsion, as well as examining the variations and distribution probabilities. Formation time of a regional caprock, composition conditions of source-reservoir-caprock, phases of hydrocarbons in migration, and all other geological factors associating with hydrocarbon generation, retention, have effects on the efficiency of hydrocarbon expulsion. The most important factors which result in the largest change of expulsion from the Qingshahou source rock in the North Shongliao basin are: depth of source rock (ZM), sedimentation rate (SR), total organic carbon (TOC %), and kerogen type index (KTI), with relative contributions (%) to the uncertainty of efficient gas/oil migration amounts at 37/32, 25/17, 19/20, and 1/15, respectively. Of these factors, KTI has a greater effect on oil migration than on gas, while SR and ZM have more effect on gas. Within the variation ranges of the thirteen major geological factors, the above four factors collectively contribute to efficient gas/oil migration amounts (m3/kg) from the Qingshahou source rock on a square (or cubic) meter basis as: 1010/1100 (3.0/3.26), 1300/1370 (3.86/4.07), 1460/1525 (4.33/4.53) and 2150/2200 (6.38/6.53), respectively, with corresponding cumulative probabilities of 16%, 50%, 68% and 84%, respectively.