Xuewei Liu

Relation between relative permeability and hydrate saturation in Shenhu area, South China Sea

Nuclear magnetic resonance measurements in hydrate-bearing sandstone samples from the Shenhu area, South China Sea were used to study the effect of gas hydrates on the sandstone permeability. The hydrate-bearing samples contain pore-filling hydrates. The data show that the pore-filling hydrates greatly affect the formation permeability while depending on many factors that also bear on permeability; furthermore, with increasing hydrate saturation, the formation permeability decreases. We used the Masuda model and an exponent N = 7.9718 to formulate the empirical equation that describes the relation between relative permeability and hydrate saturation for the Shenhu area samples.

A case study: imaging OBS multiples of South China Sea

The subseafloor structure offshore South China Sea was imaged using first-order water-layer multiples from ocean-bottom seismometer data and the results were compared to conventional imaging using primary reflections. The mirror-imaging method employs a primaries-only reverse time pre-stack depth migration algorithm to image the receiver ghosts. The additional travel path of the multiples through the water layer is accounted for by a simple manipulation of the velocity model and processing datum: the receivers lie not on the sea floor but on a sea surface twice as high as the true water column. Migration results show that the multiple-migrated image provides a much broader illumination of the subsurface than the conventional image using the primaries, especially for the very shallow reflections. The resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer (single-channel) reflection data.

Seafloor elastic parameters estimation based on AVO inversion

Seafloor elastic parameters play an important role in many fields as diverse as marine construction, seabed resources exploration and seafloor acoustics. In order to estimate seafloor elastic parameters, we perform AVO inversion with seafloor reflected seismic data. As a particular reflection interface, the seafloor reflector does not support S-waves and the elastic parameters change dramatically across it. Conventional approximations to the Zoeppritz equations are not applicable for the seafloor situation. In this paper, we perform AVO inversion with the exact Zoeppritz equations through an unconstrained optimization method. Our synthetic study proves that the inversion method does not show strong dependence on the initial model for both unconsolidated and semi-consolidated seabed situations. The inversion uncertainty of the elastic parameters increases with the noise level, and decreases with the incidence angle range. Finally, we perform inversion of data from the South China Sea, and obtain satisfactory results, which are in good agreement with previous research.

A case study: travel time inversion for P-wave velocity using OBS data of South China Sea

It is very important for converting the seismic data from the time domain to the depth domain. Here we discuss the approaches of inverse modeling of travel times for determination of the P-wave velocity (Vp). The migration section of the single channel seismic data is used to define the model horizons and help to control their geometry. Wide angle hydrophone data of OBS are used to determine P-wave travel times. The picked travel times from various shots are inverted for P-wave interval velocities using RayInvr, which calculated theoretical travel times via ray tracing. Damped least squares optimization is performed to fine tune the fits between observed and calculated travel times. In the end, the Vp curve is achieved and the results are compared with that derived from the conventional hyperbolic curve velocity analysis method, the shape of the two curves are similar, and the velocity increases in the layer where gas hydrates are present.

Erratum to: A case study: travel time inversion for P-wave velocity using OBS data of South China Sea

With this erratum Prof. T. A. Minshull withdraws co-authorship of article ‘A case study: travel time inversion for P-wave velocity using OBS data of South China Sea’ published in Volume 33, Issue 4, pages 389–396, DOI: 10. 1007/s11001-013-9167-7 as there is no contribution to the content and writing process of this article from his side. Prof. Minshull was visited by the first author in Southampton who received advice from him, but Prof. Minshull was not consulted at any stage of drafting or submitting the paper. Authors Xiangchun Wang, Changliang Xia and Xuewei Liu apologize for including Prof. T. A. Minshull’s name without his knowledge and permission.

RETRACTED ARTICLE: Analysis of P-wave attenuation in hydrate-bearing sediments in the Shenhu area, South China Sea

The article ‘‘Analysis of P-wave attenuation in hydratebearing sediments in the Shenhu area, South China Sea’’ by Chuanhui Li, Kai Feng and Xuewei Liu, Marine Geophysical Research, DOI:10.1007/s11001-014-9241-9, has been retracted at the request of the Co-Editors-in-Chief because of a substantial degree of duplication with the previously published article ‘‘Study on p-Wave Attenuation in Hydrate-Bearing Sediments Based on BISQ Model’’ by Chuanhui Li, Kai Feng and Xuewei Liu, Journal of Geological Research, vol. 2013, Article ID 176579, pages 1–8, DOI:10.1155/2013/176579. The authors had submitted their work to the Marine Geophysical Research journal clearly stating it had not been previously published, and that parts of the study had not been divided and used in different papers submitted to more than one journal. After thorough investigation, it was concluded that the authors have reused and paraphrased a substantial amount of text without referencing and acknowledging the original publication. Specifically, the two papers were found to present a high level of similarity in the following sections: ‘‘Introduction’’, ‘‘The Bisq model’’, ‘‘Effects of ‘pore-filling’ hydrates on the rock properties’’, ‘‘P-wave attenuation analysis in hydrate-bearing sediments’’, ‘‘Actual application’’ and ‘‘Conclusions’’.