The Chang 8

1

sandstone reservoir in Xifeng oilfield

Ordos basin

is mainly composed of lithic arkose and feldspathic lithic sandstone

and is of typical low porosity and low permeability reservoir with an average porosity of 8.32% and average permeability of 1.33×10

-3

μm

2

.The reservoir has experienced diagenesis

metasomasis

dissolution and cataclasis

and is now in the late diagenetic phase A to B.The mechanical compaction in the early diagenetic phase and the ferruginous carbonate cementation in the late diagenetic phase are the main contributors to the poor poroperm characteristics.According to the characteristics of diagenesis

the braided ri-(ver) delta front sandbody in the study area can be divided into 4 diagenetic facies belts

including compaction and pressolution

weak compaction-carbonate cementation

weak compaction-chlorite-film cementation

and chlorite-film cementation-feldspar corrosion.Sandstones in the latter two facies belts in the core of the main sandbody have good poroperm characteristics and oil-bearing properties

thus they are favorable for hydrocarbon accumulation.