China University of Petroleum

About: China University of Petroleum is a education organization based out in Beijing, China. It is known for research contribution in the topics: Catalysis & Oil shale. The organization has 39802 authors who have published 39151 publications receiving 483760 citations. The organization is also known as: Zhōngguó Shíyóu Dàxué & China University of Petroleum (Beijing).

High Vp/Vs ratio: Saturated cracks or anisotropy effects?

Abstract: [1] We measured Vp/Vs ratios of thermally cracked Westerly granite, thermally cracked Carrara marble and 4% porosity Fontainebleau sandstone, for an effective mean pressure ranging from 2 to 95 MPa. Samples were fluidsaturated alternatively with argon gas and water (5 MPa constant pore pressure). The experimental results show that at ultrasonic frequencies, Vp/Vs ratio of water saturated specimen never exceeded 2.15, even at effective mean pressure as low as 2 MPa, or for a lithology for which the Poisson’s ratio of minerals is as high as 0.3 (calcite). In order to check these results against theoretical models: we examine first a randomly oriented cracked medium (with dispersion but without anisotropy); and second a medium with horizontally aligned cracks (with anisotropy but without dispersion). The numerical results show that experimental data agree well with the first model: at high frequency, Vp/Vs ratios range from 1.6 to 1.8 in the dry case and from 1.6 to 2.2 in the saturated case. The second model predicts both Vp/Sv and Vp/Sh to vary from 1.2 to 3.5, depending on the raypath angle relative to the crack fabric. In addition, perpendicular to the crack fabric, a high Vp/Vs ratio is predicted in the absence of shear wave splitting. From these results, we argue the possibility that high Vp/Vs ratio (>2.2) as recently imaged by seismic tomography in subduction zones, may come from zones presenting important crack anisotropy. The cumulative effects of crack anisotropy and high pore fluid pressure are required to get Vp/Vs ratios above 2.2. Citation: Wang, X.-Q., A. Schubnel, J. Fortin, E. C. David, Y. Gueguen, and H.-K. Ge (2012), High Vp/Vs ratio: Saturated cracks or anisotropy effects?, Geophys. Res. Lett., 39, L11307, doi:10.1029/2012GL051742.

Mechanisms for oil depletion and enrichment on the Shijiutuo uplift, Bohai Bay Basin, China

Abstract: The Shijiutuo uplift is a major uplift to the north of the Bozhong depression, the largest generative kitchen in the Bozhong subbasin, Bohai Bay Basin. Although the N35-2 trap on this uplift contains a medium-size oil accumulation and the Q32-6 trap contains China's third largest offshore oil accumulation, the Q31-1 trap between the N35-2 and Q32-6 traps with very similar evolution history was confirmed to be dry. Biomarker associations of crude oil and source rock samples were analyzed, and three-dimensional migration pathway modeling was conducted to investigate the origin of oils and mechanisms for oil enrichment and depletion on the uplift. Multiple-parameter oil-source correlation and hierarchical cluster analysis using 10 selected biomarker parameters allowed the identification of four source-related oil classes. Almost all oils from the Shijiutuo uplift are derived from the Eocene Shahejie Formation, whereas oils found between the Shijiutuo uplift and the Bozhong depression either are derived from or have important contributions from the Oligocene Dongying Formation. Variations in oil classes and biomarker parameters suggest sequential migration of oil generated from the Shahejie and then Dongying formations in the Bozhong depression, which is reasonably supported by petroleum migration pathway modeling. Oil charge from two oil-prone source rock intervals and, more importantly, focusing of oil originating from a large area of the Bozhong generative kitchen into the same trap accounted for oil enrichment and formation of China's third largest offshore oil field in the Q32-6 structure. The complexity and primary control of the sealing surface (top surface of the carrier bed) morphology on the positions of migration pathways caused the Q31-1 trap to be shielded from migration of oil originating from the Bozhong depression, resulting in oil depletion in this trap. Shadows to petroleum migration may occur because of the three-dimensional behavior of petroleum migration, and two-dimensional migration modeling may be misleading in predicting petroleum occurrences.