SEDIMENTARY MECHANISM AND RESERVOIR IMPLICATION OF GRAINED CARBONATE IN SHENGLI OILFIELD

In this paper, the Paleogene grained carbonate rocks in the Shengli oilfield, east of China are divided into six types: oolitic dolomite, sand-clastic dolomite, gastrapod-clastic limestone or dolomite, ostracod-clastic dolomite, multigrain-filled matrix dolomite and calcareous sparry grain-clastic dolomite. The sedimentary mechanism of grain-clastic carbonate rocks is described herein based on the analysis of the disturbance and transportation process of grained clasts along the coast and around the platform, and on the determination of two types of energy-reducing topography caused by the subaqueous topographic rise in the barrier bay and the off-shore area. An empirical formula: W=RG, where R represents the average diameter of the grained clasts and G represents the percentage content of the grained clasts in the rocks, has been used to determine the W, a water-body energy index. This formula can also be used to identify five facies zones in this region: the super-high energy grade (W > 50), high energy grade (W : 25~50), medium energy grade (W : 10~25), low energy grade (W : 1~10) and static water grade (W < 1). The comparison coefficient (the sorted coefficient) can be used as an index to identify the wave energy and the water -body energy in a sedimentary zone. The carbonate reservoir can be divided into four types of permeability layers: primary superhigh, secondary high, secondary medium-low and primary low permeability layers, in line with the physical properties caused by the deposition and post-depositional reconstruction of the grain-clastic carbonate rocks.