Regularities of changes in fluid composition and properties in Vankor field pools: from light to heavy oil

Abstract

Oil in layers Nkh 3-4, Nkh 1, Sd 9, Yak 3-7 and vYak 2-4 of the Vankor field occurs at the depth of -2,767 to -1,357 meters at strongly different temperatures: from 62 to 26 °C. Such temperature conditions contribute to oil biodegradation processes in the pool. Therefore, oils in different pools significantly differ from each other in terms of composition and properties depending on the intensity of biodegradation. At the same time, pools might embrace both oils that have practically been not exposed to biodegradation processes and significantly biodegraded oils. The most seriously altered oils are found in vYak 2-4 layer pools. They are the heaviest and the most viscous oils among the samples under study. Many typical oil components (alkanes, alkylbenzenes, naphthalenes, phenanthrenes, dibenzothiophenes) are absent in their composition. Besides, the initial distribution of hopanes in the composition of biomarkers is altered. Apart from the molecular composition of degassed oil samples, the work also studies the effect of biodegradation on the properties and the component and isotopic composition of oils, gases and formation fluid samples.