Quality control of the positioning data in ultra high resolution reflection seismics

• Autor(a) principal: Francisco, Andrade António
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30581
• topic: GeoSurveys; RadExPro; 3D UHRS; Quality control; Navigation data; Positioning errors; DGPS; Offset; Direct arrivals; Rejection of the navigation data

The quality control is a very important operation in the seismic data acquisition surveys and its main goals are to assess the quality of the acquired data, to detect problems during acquisition and finally to guarantee that the data has the required quality to be accepted for further processing, or if it must be rejected. The time spent in operations makes its cost to grow up and therefore the QC must be done efficiently and as early as possible., It is critical that the most relevant factors that can seriously compromise the data are evaluated onboard. Navigation quality control is extremely important because the navigation errors can contribute to the feathering effect that by itself is one of the main rejections criteria. On the other hand, the quality of the positioning data can have strong influence on the seismic resolution, as it is used to calculate positioning for every reflection point. Thus, wrong positioning data affect offsets computing and can move the reflection midpoints to erroneous position causing a discrepancy between the actual geology and the seismic section obtained. This causes errors in the exact location of boulders and the identification of other in-depth hazards that threat the optimization of wind turbine installations, which is one of Geosurveys goals in this type of surveys. The main sources of these problems are related to the bad functioning of GPS antennas used in the acquisition system and other systematic problems such as geometry assignment. There are typical errors which affect the geometry such as distance measurement between lead buoy center and first channel, distance measurements and assignment between channels in the different streamer sections. The solution proposed in this work consists on the development of effective methods to diagnose these types of problems, where through a graphical scheme it becomes possible to detect different types of positioning errors and their causes. The method developed in the scope of this work was based on the quality control of the offsets calculated with the positioning data and the direct arrivals time. With this information it was possible to establish a classification criterion for the positioning data according to its quality, to calculate the errors and obtain indicators about its source of error, always considering that the various factors have different influences on the errors and some problems appear more frequently than others. Based on this, rejection criteria for data with positioning errors was established and solutions were tested in the software packages RadExPro and Kingdom Suite, in order to evaluate the effect of these errors on the seismic volumes.