The Application of Hydropyrolysis Technology in Oil-Source Correlation of Petroleum Systems within the Precambrian and Lower Paleozoic Sedimentary Record
Liangliang Wu, Yuhong Liao, Yunxin Fang, and Ansong Geng
The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, P.R. China
With the petroleum exploration going forward deeper strata, Precambrian and Lower Paleozoic sedimentary records have attracted great attentions of petroleum geologists. Unfortunately, most of those old strata are high-over maturity and only have low concentration of extractable organic matter (EOM). Since generally they have been buried deeply and experienced long geological history, the biomarkers obtained by regular geochemical methods (Soxhlet extraction for example) from high-overmature source rocks are too low to satisfy the requirement of instrumental analysis. And they are also easily interfered by biomarkers in recent sediments and migrated hydrocarbons. Meanwhile, the source-related biomarker parameters extracted from high-overmature source rocks would become a similar developing pattern and cannot represent the original characteristics of organic matter.
Catalytical hydropyrolysis (HyPy) technology refers to an open-system pyrolysis at high hydrogen pressures (>10 MPa) in the presence of a dispersed sulphided molybdenum catalyst. HyPy can release higher yield of EOM than Conventional procedures. Furthermore, for both bitumens (Liao et al., 2012) and kerogens (Wu et al., 2012), thermal maturation have much lower influence on the covaltenly bound biomarkers released by HyPy than on free biomarkers extracted by Soxhlet extraction. The results by Wu et al. (2012b) indicated that the source-related biomarker parameters such as the distribution of C27-29 ααα20R steranes, the ratios of the TT23/H30 and the H29/H30 were quite stable in the HyPy products of various maturities (Ro≤2.4%). That means the covalently bound biomarkers released from high maturity solid bitumen and kerogen are comparable with the free biomarkers obtained by Soxhlet extraction.
Here we provide an example of oil-source correlation in the Tianjingshan structure of the northern Longmen Mountain (Wu et al., 2012a). There are two primary source rocks in this region, the overmature Infracambrian-Lower Cambrian source rocks and the mature upper-Permian source rocks. HyPy was used to release covalently bound biomarkers from the overmature Lower Cambrian kerogen. The ratios of C23 Tricyclic tepanes/C24 tetracyclic terpanes (TT23/tT24) and pregnane/homopregnane (S21/S22) in Lower Cambrian bitumens and are very similar to that of those HyPy products, but higher than that of the Upper-Permian source rocks. Based on the data from HyPy products, it showed that the Infracambrian-Lower Cambrian source rocks are most likely to be correlative with the Lower Cambrian bitumens, which is also proved by the Triaromatic steroid hydrocarbons in aromatics of Soxhlet extract and Bulk isotopic values. Though the evidences from biomarkers indicated that the Permian oil seep was sourced from Infracambrian-Lower Cambrian source rocks, the bulk δ13C value of the Permian oil seep is intermediate between the Infracambrian-Lower Cambrian source rocks and the Upper-Permian source rocks. Furthermore, the Permian oil seep and the Upper-Permian source rocks have similar δ13C values of individual n-alkanes. We speculate that the Permian oil seep was charged at least twice. The first charged oil was from the Infracambrian-Lower Cambrian source rocks and then charged by the oil from the Upper-Permian source rocks.
AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013