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Superimposed secondary alteration of oil reservoirs. Part I: Influence of biodegradation on the gas generation behavior of crude oils
Organic Geochemistry ( IF 3 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.orggeochem.2019.103965 Yuhong Liao , Weimin Liu , Yinhua Pan , Xiaofeng Wang , Yunpeng Wang , Ping'an Peng
Organic Geochemistry ( IF 3 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.orggeochem.2019.103965 Yuhong Liao , Weimin Liu , Yinhua Pan , Xiaofeng Wang , Yunpeng Wang , Ping'an Peng
Abstract Due to multi-stage tectonic movements, many oil reservoirs in typical superimposed basins of China have undergone more than one secondary alteration. Typically, these oil reservoirs experienced biodegradation at an early stage followed by thermal alteration at a later stage. The extent of each secondary alteration can be variable. Here, the succession of biodegradation and subsequent thermal alteration is called superimposed secondary alteration. This study aims not only to show the superimposed secondary alteration process in the reservoir by laboratory simulations, but also to show how varying extents of biodegradation influence the gas generation behavior of crude oils under thermal stress. Hydrocarbon gas generation potential is significantly reduced at the low to moderate biodegradation stage because of the selective removal of normal and branched alkanes. Hydrocarbon gases generated from the more severely biodegraded oils are drier, attributable to the decreasing yields of C2–C5 gases relative to methane. In the oil-generative window, the methane generated from more severely biodegraded oils is relatively enriched in 13C. Kinetic modeling suggests that moderately and severely biodegraded oils are thermally less stable than the non-biodegraded and slightly biodegraded oils. The bulk hydrocarbon gas yields from the non-biodegraded oil do not exceed those from the moderately biodegraded oils until EasyRo > 1.6%. For EasyRo of 1.6–2.5%, pyro-bitumen yields from heavily to severely biodegraded oils were about 2–4 times that of non-biodegraded oil. That is, the gas yields normalized to the weight of pyro-bitumen from heavily to severely biodegraded oil is only 25–50% of the gas yield of non-biodegraded oil. Therefore, hydrocarbon gas resource potential based on pyro-bitumen content must be very carefully considered in cases of superimposed secondary alteration.
更新日期：2020-04-01
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