Controls on Heavy Oil and Tar Sand Bitumen Compositions and Physical Properties in the Liaohe Basin, Northeast China

Haiping Huang, Barry Bennett, Thomas B.P. Oldenburg, Jennifer Adams, Kim Noke, and Steve R. Larter
University of Calgary, Calgary, AB

Heavy oils and tar sands dominate the world petroleum resource and are produced by biodegradation of normal crude oils. The effects of biodegradation are empirically well known, but the processes involved, the fraction of oil destroyed and the critical factors controlling degradation and the impact of oil mixing processes on fluid properties remain obscure. A suite of oils and reservoir core extracts from the Liaohe basin, NE China, was analyzed to investigate the effects and controls of biodegradation on petroleum composition and physical properties. Systematic changes in oil physical properties are reflected in marked gradients in petroleum bulk composition, component concentrations and molecular indicators throughout biodegraded oil columns. A variety of factors control reservoir biodegradation; these include reservoir temperature and thermal history, oil residence time and charge history, fresh oil in-mixing, the structure of the reservoir, water-leg size, nutrient supply and other factors. Based on an oil charging-biodegradation model mass balance calculation, up to 50% of petroleum mass has been depleted at level 5 biodegradation in these reservoirs, beyond this level of biodegradation loss of oil mass is less significant. The biodegradation model proposed for the Liaohe heavy oilfields couples geochemical and geological factors to provide a coherent approach to ascertain the impact of degradation and oil mixing on petroleum properties. Our geochemical approach can be used to locate sweetspots, optimize the placement of new wells and improve definition of completion intervals and help with production allocation from long production wells. We illustrate the approach with field examples.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005