Reservoir Characteristics Of The Mid-sha-3 Member, ShaHejie Formation, Eogene In Puwei Sag

Dongpu depression, a oil-gas bearing basin, is situated in the southwest Bohaiwan basin. Puwei sag is a subunit that is tectonically located in the north central upheave of Dongpu depression.According to theory of multidisciplines, the reservoir characteristics of the Mid-sha-3 member, Shahejie formation, Eogene in Puwei sag have been studied by means of the combination macroexamination with microexamination and regional with well data as well as the investigation in the field with research indoors. The research as follows that four sedimentary facies are recognized, which include lacustrine faeies(coast and shallow lake-storm belt or deep and hemi-deep lake belt) and sublacustrine fan and delta and deep water salt lake facies. Main reservoir bodies include the river sandbodies of sublacustrine fan and the subaqueous distributary channel sandbodies in the delta front as well as sandstone dam in coast and shallow lake.Feldspar lithic sandstone and lithic feldspar sandstone are main reservoir rock types in the Puwei sag. Those rocks with moderate maturation in composition and bad maturation in texture have experienced diagenesis of mechanical compaction and cementation as well as metasomasis and dissolution. The types and characteristics of porosity are affected by the diagenesis. The mechanical compaction and cementation are major factors to make reservoir to lose porosity. The dissolution playing an important role to improve reservoir quality is favorable for secondary pores,. Carbonate cementing are developed and distributed universally in the Puwei sag.Based on synthesis analyses of autogenous minerals associations and clay minerals transform and pore types as well as evolution of organic matter etc. the two diagenetic stages are divided into B phase of early diagenesis and A phase of late diagenesis in the Mid-sha-3 member of Shahejie formation. The pore types of reservoir are divided into three types such as the primary pore and secondary pore and fissure . The different pore texture grade have been made out and pore texture grade of the Mid-sha-3 member of Shahejie formation in Puwei sag reaches only II and III grade.There are favourable source-reservoir-cap rock assemblage and trap conditions in the sag. These can lead that accumulation of oil and gas is favourable in the sag. On the studying basis of depositional facies belt and sandstone body distribution with the reservoir quality as well as logging and so on, evaluation has been carried out for sand-bearing beds from the Mid-sha-3 member, Shahejie formation in Puwei sag. It is concluded that the best is thinked as the 4 sand-bearing bed and the second as 8 sand-bearing bed and the worst as 3 sand-bearing. Finally, favorable block for oil and gas to accumulate is predicted that the first favourable block is V67-V68-V69-P86 in the middle of the west sag and V355-V86-V370 in the northwest, the second is P77-P139-P80-P138 and the third is P65-P75-P100-P126.