Yao Suping

Discovery of low-mature hydrocarbon in manganese nodules and ooze from the Central Pacific deep sea floor

Extracts from manganese nodules and ooze from the Central Pacific deep sea floor were analyzed using the chromatogram-mass spectrum, and it was found that most of the biomarker molecules are of the low-mature type (some have characteristics of mature): the ratio of “A”/C is high between 11.4%–19.75%; CPI is 1.22–1.23; C31-22S/ (22S+22R) hopane is 0.59–0.60, Tm/Ts is 0.99–1.99; βa moretane/(aβ+βa) hopane is 0.12 – 0.14; C29 sterane 20S/(20S+20R) is 0.35 – 0.41; ββ/(ββ+αα) is 0.38 – 0.45; arene TA(I)/TA(I+II) is 0.16–0.21; methyl-phenanthrene index (MPI1) is 0.35–0.67. According to the geological settings of the sampling area and its organic geochemical characteristics, it is considered that the hydrothermal activities on the ocean floor facilitate the decomposition of organic matter in the sediment, which leads to the generation and migration of hydrocarbon into manganese nodules and ooze. This discovery is important for understanding the mechanisms of hydrocarbon generation in the ocean floor and for expanding the potential of oil and gas exploration in the ocean.

Mn content of reservoir calcite cement: A novel inorganic geotracer of secondary petroleum migration in the tectonically complex Junggar Basin (NW China)

Electronic probe microanalysis (EPMA) results of reservoir calcite cement from fourteen core samples in the Junggar Basin show that Mn-content varies largely between different samples from below the detect limitation to 4.14%, while it displays a generally good correlation with oil-gas shows. This, therefore, likely indicates that concentration of the Mn-content of the calcite cement has a close relation to the intensity of petroleum fluid charging during hydrocarbon secondary migration. In order to assess this hypothesis, oxygen and strontium isotopic measurements on sixteen calcite veins host in source sequences were carried out to investigate the feature of the oil-source petroleum fluid. Analytical results imply that during hydrocarbon generation and migration, deep hot fluid has dissolved volcanic minerals interlined between mudstone source rocks. As Mn is a kind of typical trace element enriched in volcanic rocks, it is reasonable to conclude that the petroleum fluid formed in the source sequences would be Mn-rich. Consequently, calcite cements precipitated from such Mn-rich petroleum fluid would be Mn-rich accordingly. Due to the geologic chromatographic effect during migration along reservoir rocks, the decreasing of the Mn-content of the reservoir calcite cements indicates the migration direction. Then, this novel geotracer was further successfully applied in the study of hydrocarbon migration in the Junggar Basin in combination with organic geochemical analyses during the hydrocarbon migration. The Mn content of the reservoir calcite cement appears promising as a novel inorganic geotracer for the petroleum migration. This paper represents a search for novel indicators of secondary petroleum migration in tectonically complex basins based on fundamentals of the reservoir fluid-rock interactions.

Physical Properties of the Triassic Host Strata and Their Relations With Gold Mineralization in Youjiang Rift, South China

Micro-fine disseminated gold deposits are hosted in the Triassic Baipeng Formation (argillaceous siltstone and arenaceous mudstone) in the Youjiang Rift, South China. Physical properties (grain size, specific surface, porosity and permeability) of the host rocks are studied with respect to ore-fluid circulation, water-rock reaction and the effective volume from which ore-components could be extracted. On this basis, it is considered that the ore-fluid and ore-metals were extracted mainly from the strata and hydrothermal solutions, tending to move towards low-energy sites, depositing their gold in fault zones at the margins of the basin and in the circle fracture systems around underwater uplifts. The gold deposits resulted from the deep-circulation of hydrothermal solutions, probably aided by multi-stage superimposition. The quantities of ore-fluid necessary to form the deposits were estimated.