Zhang Linye

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.

Control of pressure system development on reservoir formation in the Dongying Sag, Shengli Oilfield, East China

Abstract The zonality of abnormal pressure is closely correspondent to the breakthrough pressure (or pressure preservative ability) of mudstones in the Dongying Sag. The breakthrough pressures and formation fluid pressure coefficients rise with increasing depth. The preservation of isolated mudstone intervals is also important to the abnormal pressure formation. Based on the episodic difference of pressure buildup mechanism, source dynamic (fluid pressure in source rocks) fields of critical geologic times were analyzed in lateral plane and vertical profiles in the Dongying Sag. Source dynamic of major source rocks occurs in disequilibrium with time and space, which affects oil-gas sources and reservoir formation and controls the direction of oil-gas migration as a whole. The present reservoirs are distributed along the pressure decreasing directions. The distribution of the reservoirs is successional to the evolution of source dynamic. On the other hand, oil-gas migration and accumulation affect the distribution of formation pressure fields. The isolated mudstone intervals preserve the fluid pressures to different extents. Due to the equilibrium between pressure buildup and pressure relief, source dynamic creates different conditions in various pressure systems during its transference, which cause the differences in types and features of oil-gas reservoirs. Based on the evolutionary history of source dynamic, the reservoir forming process in the Dongying Sag was analyzed. The deep layers of the Shahejie Formation are important targets for us to discover light hydrocarbon and natural gas reservoirs with high pressures.

Organic compositions of lacustrine source rocks in Jiyang super-depression and its implication to petroleum geology

The compositions of organic matter in four immature source rocks from Tertiary strata of Jiyang super-depression, the most typical continental rift subsidence basin in East China, have been studied by different extracting methods with CHCl3, MAC and CS2/NMP, respectively. The results suggest that there are great differences among the chemical compositions of organic matter in the source rocks derived from different depositional environments. About 79% of all the organic matter exists by non-covalent bond in the Es4 source rocks which were deposited under the saline lacustrine, indicating that its organic matter is not the real kerogen, but mainly composed of soluble organic matter which is easy to generate hydrocarbon at lower temperature. This is why the immature oils were derived from Es4 source rocks in Dongying depression. In contrast, around 60% of organic matter exists by covalent bond in Es3 source rocks which were deposited under the deep brackish-fresh lacustrine, showing that Es3 source rocks are mainly composed of kerogen producing mature hydrocarbon at higher temperature. The thermal simulation experiments, upon the remaining solid source rocks which were sequentially extracted by the three solvents, have been carried out. The chloroform extracts from the simulation product have been compared with the other three solvent extracts gained at room temperature. It is obvious that remarkable odd/even predominance (OEP) is mainly the characteristic of soluble organic matter; phytane mostly exists in the soluble organic matter by means of non-covalent bonds and characteristics of soluble organic matter are similar to these in immature oils produced in Jiyang super-depression.

Identification and significance of 3β-alkyl steranes in the Eogene lacustrine sediments and petroleum of China

Several homologous series of steranes with alkyl side chains (C1 to C4) at the 3β position have been identified in the Jiyang Eogene lacustrine deposition. It is postulated that its precursors represent a new class of steroids, alkylated at the C-3 position with a polyhydroxy n-alkane. These precursors may have been formed by the bacterial addition of a ribose sugar to Δ2-sterenes, diagenetic alteration products of steroids synthesized by eukaryotes. 3-alkyl steroids might substitute for hopanols in bacterial membranes. When they are present in a sample, the patterns of the isomer distributions of 3-alkyl steranes are similar to desmethyl steranes except for lower rearranged ones. It is shown that the configurational isomerization of 3-alkyl steranes is trending in line with that of desmethyl steranes with increasing of maturity. The abundance of 3-alkyl steranes may be controlled by the depositional environments; they are primary in saline or near shore lacustrine, moderate in shallow lacustrine, poor in sub-deep to deep lacustrine relative to the 4-methyl steranes.