Reservoir characteristics and potential of a shallow-marine multi-level fan in the Miocene Huangliu Fm. within the DF1-1 gas field (Yinggehai Basin, S China)

Abstract

Deep-marine fans receive much attention because of their high potential for hydrocarbon exploration. Shallow-marine fans are much rarer and less well investigated. Particularly the formation and reservoir distribution of shallow-marine multi-level submarine fans are still hardly understood. Integration of data from cores, well logs, 3D seismics, in combination with analyses of thin-sections, porosity and permeability of Member 1 of the Miocene Huangliu Formation in the DF1-1 Gas Field of the Yinggehai Basin (S China) has provided much new information on the characteristics, development, and hydrocarbon potential of the reservoirs in such a type of fan. The study indicates that the IIb Gas Level of this member is built of three 5th-order sequences. The fan consists of channels, levees, ‘overbank’ sand sheets, and pro-fan silt- and mudstones. The development of this fan was controlled mainly by alternating subcritical and supercritical gravity flows, sediments supply and relative sea-level fluctuations. The NW-SE running channels occur on three slightly different levels that form 3 zones with chutes-and-pools morphology, which results in a multi-level submarine fan with zones of different sand thickness. The sand content of the channels and sand sheets is commonly higher than 50%. The reservoir sands underwent intermediate compaction and show mainly primary intergranular pores with short contacts. The porosity is 13.7–19.5% and the permeability ranges from 3.2 to 14.2 mD. The best reservoirs are the sand sheets, followed by channel sediments. The various reservoirs are commonly not interconnected due to lithological and stratigraphic traps. A new reservoir distribution model of submarine fans could thus be developed, which will facilitate oil and gas exploration.