Abstract
Based on the data of core observation, grain size analysis, micro paleontology, logging and well logging, the sedimentary environment and characteristics of NmIII and NmIV oil formation in the lower Minghuazhen Formation of B19-4 Oilfield are studied, and the formation reason of narrow strip sand body in this area is explained. The characteristics of formation thickness, lithology, paleontology and sedimentary microfacies indicate that the lower Minghuazhen Formation of B19-4 Oilfield belongs to the shallow water delta deposition of continental lake basin in the background of rising to falling from base level. The sedimentary environment is characterized by gentle slope, large accommodation space, weak hydrodynamic force, far-reaching sediment source, relatively stable structure, etc. the sedimentary sand body is dominated by distributary channel deposition, with developed natural dikes, and undeveloped mouth bars and crevasse fans. Because of this sedimentary environment, the underwater distributary channel of the shallow water delta is not easy to be changed, and the sand bodies of the underwater distributary channel of the multi-stage sedimentary cycles are vertically superposed, forming the sand bodies with narrow strip distribution.
Highlights
The Neogene Lake Basin of Bohai Bay basin developed in the lower depression stage of the basin as a whole, which was filled up by the peneplanarization during the deposition period of the Guantao Formation
Because the channel sand body is in a narrow strip, previous studies have considered that the area belongs to shallow delta narrow channel deposition, and no study has been made on its genesis
It is considered that the channel width of the NmIII and NmIV oil groups in this area ranges from 250 to 300m; the thickness of sand bodies in a single stage ranges from 2 to 9m; the width-to-depth ratio ranges from 28 to 150; and it belongs to the underwater distributary channel deposition in shallow-water delta of continental lake basin [5, 6]
Summary
The Neogene Lake Basin of Bohai Bay basin developed in the lower depression stage of the basin as a whole, which was filled up by the peneplanarization during the deposition period of the Guantao Formation. It is considered that the channel width of the NmIII and NmIV oil groups in this area ranges from 250 to 300m; the thickness of sand bodies in a single stage ranges from 2 to 9m; the width-to-depth ratio ranges from 28 to 150; and it belongs to the underwater distributary channel deposition in shallow-water delta of continental lake basin [5, 6]. Lacustrine Delta---Case Study of B19-4 Oilfield, Bohai Bay Basin narrow strip sand body, it is considered that the narrow strip sand body is not formed by the deposition of narrow deep channel, but by the superposition of multi-stage distributary channel sand bodies in shallow water delta. This study breaks the original understanding of the area and explains the cause of formation of narrow strip sand body It is a useful exploration of distributary channel of shallow Delta. Deposition Environment of Underwater Distributary Channel in Shallow-Water Delta
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