On the Differences of Reservoir Quality of Shahejie Fm. in Steep Slope Zones of Jiyang Sag

Key words: 
• Jiyang sag /
• Shahejie Fm. /
• clastic reservoir /
• diagenetic evolution /
• difference of reservoir quality

Abstract: Coarse sediments of nearshore subaqueous fan or fan delta were mainly developed in the third member or the forth member of Shahejie Formation in steep slope zones of different depressions in Jiyang sag, such as nearshore subaqueous fan in the north of Dongying depression (Li 88 well region) and Chezhen depression (Che 66 well region), delta in the north of Huimin depression (Jishan Sand Body), and fan delta in the north of Zhanhua depression (Yi 170 well region). But their sedimentary types and compositions were different. Great amounts of data from cores and reservoir analysis demonstrated that the reservoir of Shahejie Fm. had undergone a series of diagenesis, such as compaction, cementation, dissolution and replacement in burial diagenetic evolution, resulted in the low porosity and permeability reservoirs. Although it showed the similarity of the burial depth (mostly 2 000~3 000 m) and diagenesis evolution stages (the middle diagenetic phase) of Shahejie Fm. in Jiyang sag, differences of reservoir quality in these steep slopes of different depressions still existed. These kinds of differences were caused by sedimentary condition and diagenetic evolution differences. Under the same burial depth and diagenetic evolution stages, dissolution process had played a significant role in improving reservoir quality (the porosity up to 20% and the permeability up to 60×10^-3 μm²). The comprehensive research results of reservoir controlling factors and characteristics indicated that, the favorable reservoirs of Shahejie Fm. in the steep slope of Jiyang sag developed in the depth about 2200m in Dongying, Chezhen and Huiming depressions, and the depth of 2 900 m in Zhanhua depressions. The channel sandbodies originated from delta and nearshore subaqueous fan, which were rich in dissolution pores, would be the favorable exploration targets in the future.