--> --> The Application of Seismic Sedimentary Method in the Detailed Prediction of the Lithological Reservoir of Sublacustrine Fan in Bohai JZX Gasfield

2018 AAPG International Conference and Exhibition

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The Application of Seismic Sedimentary Method in the Detailed Prediction of the Lithological Reservoir of Sublacustrine Fan in Bohai JZX Gasfield

Abstract

With the ongoing exploration and development of Bohai oilfield, the lithological oil and gas reservoirs of sublacustrine fan are becoming one of the important targets for breakthrough. However, because of lack of exploration data, large spacing and low resolution of seismic data, it is very difficult to predict the horizontal distribution and communication relationship of small-scaled lithological reservoir of sublacustrine fan in the study of early development of offshore medium-deep lithological oilfields. This paper is a case study of the sublacustrine fan of the lower second member of Dongying Formation of Bohai JZX gasfield. In this paper, the minimum isochronal strata units are established through strata correlation and stratigraphic slice.Seismic stratigraphic slice, frequency division interpretation, and variance analysis integrated with geological pattern recognition are applied to detailed prediction of lithological reservoir of the sublacustrine fan. Resolution of the conventional main frequency seismic profiles is improved by method of frequency division interpretation.Under the guidance of seismic sedimentology, variance cube attributes of different periods are chosen to characterize the horizontal distribution and vertical evolution of the sublacustrine fan sand bodies. Based on single well facies, log facies and seismic facies, through attribute optimization of horizontal and vertical seismic facies, average instantaneous frequency and dip angle within superiority frequency band are chosen to characterize the differences between various sedimentary subfacies. Three subfacies including inner, middle and outer fan are characterized to establish the detailed sedimentary pattern. Under the guidance of sedimentary pattern and integrating with fluid seismic response characteristics, forward modelling and hydrocarbon accumulation pattern, the inner communication relationship between subfacies is carefully studied. The results show that the middle fan is unconnected with the outer and that the inner fan at structural heights has the risk of no hydrocarbon accumulation. In the context of current low oil prices, this study effectively lowers the investment risks in the early development of the gasfield. The methods have reference significance and revelation for the exploration and development of other sublacustrine fan gasfields, thus have good application value.