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Integrating Geophysics With Geology to Predict Sand Body Distribution in Fault Basin

Abstract

Accurate sand body prediction is the key to explore oil and gas in continental rift basin. It can determine not only the reservoir distribution but also the migration direction of oil and gas. The reservoir changes quickly in horizontal for the multiple sources and sedimentary cycles in the continental fault basin. It is difficult to descript sand body for the multiple solutions of seismic data. In the long term exploration practice, we summarized a set of methods integrating tectonic evolution history, ancient landform features, sequence structure characteristics, drilling data and seismic attributes to indentify and describe sand body. The main research includes follows: (1)Integrating well logging and seismic data to establish third order sequence framework in sag and fourth order sequence stratigraphic framework in target area. Then division different sedimentary bodies according to sedimentary model and seismic attributes in the sequence framework. (2) Ascertaining source area and the formation mechanism of the sedimentary body by integrating the characteristics of the ancient landform, the tectonic evolution history, the sedimentary body location in sequence framework and the characteristics of seismic reflection. (3) Provenance analysis to ascertain different components of erosion production and their characteristics of seismic reflection. (4) integrating characteristics of ancient landform, sequence framework and seismic reflection to identify sand bodies and describing their spatial distribution. (5) Integrating sand body spatial distribution, ancient landform, fault system to ascertain the migration direction of oil and gas and favorable traps. Based on the above methods, we successfully explored many oil and gas fields. In the middle section of E2S3 of Laizhouwan Sag in Bohai Bay Basin, by building high resolution sequence framework, 6 stages of braided delta front sand bodies, 2 slope displacement fans and turbidity fan were described, which proved more than 100 million square of oil. In steep slope of Shijiutuo Uplift, 5 subaqueous fans were identified under the maximum flooding surface of E3d3. By analyzing the contact relationship among the spatial distribution of fans, fault system, and hydrocarbon source rock, distribution of oil and gas was accurately predicted in Paleogene and Neogene, and proved more than 100 million square of oil. We hope this study can provide reference for oil and gas exploration in other areas.