The Characteristics Of Paleogene Reservoirs And Their Forming Mechanism In Chezhen Area

On the basis of observation and description of cores, materials of seismic, logging and tests, this paper studied reservoir characteristics, controlling affects and formation mechanism of deep reservoirs of Paleogene in Chezhen sag.Deep reservoirs of Paleogene in Chezhen sag was a sedimentary system which includes alluvial fan, fan delta, lacustrine facie, coastal fan, sublacustrine fan and half deep-deep lacustrine deposition formed in abrupt slope. The main types of reservoir spaces include pores and cracks. Pores in the reservoirs are most secondary pores and composite pores and merely primary pores and formed by the denudation of organic acid in overpressured environment. Cracks include structural cracks, overpressure cracks and lithogenic cracks and formed on the founction of tectogenesis and diagenesis.On the basis of the comprehensive analysis of geothermal field and pressure field and flow field, the diagenesis in the formation of interest of this area includes compaction, cementation, metasomasis and dissolution. Usually, dissolution is benefit for the improvement of reservoir quality but compaction, cementation and metasomasis does harmful. In addition, the early cementation can reject the latter compaction to benefit the reservoir.According to the comprehensive analysis of diagenesis types, degree of organic metamorphism, types, formation order, degree of dissolution of diagenetic minerals and types and content of clays in the microscope, reservoir in the formation of interest of this area can be divided into A stage and B stage of middle diagenesis. In it, A stage of middle diagenesis can be divided into A1–substage and A2–substage. And the reservoirs also can be divided into 3 typed of diagenetic facies and they are strong compaction consolidation diagenetis facies, carbonate cemented diagenetic facies and unstable component dissolution diagenetic facies.The controlling affects of quality reservoir include structure, sedimentary, diagenesis and water-rock. And sedimentary and diagenesis is the most important affects and structure is the vital function to control and reform the reservoir while the flow reforms the reservoirs by diagenesis.