Study On The Fluid Inclusions And Petroleum Migration Of Denan Depression

Denan sag, located in southwest Dezhou city, Shandong province, is the northeast part ofLinqing depressionin Bohai bay basin. Exploraed area is approximate 310 square kilometers. It isfan-shaped in the plane and extends the directions respectively to northwest and northeast.Composed of the main body low-lying and the Taitoushi hypo-low-lying, Bixuedian noseconstruction belt between them, the whole structure characteristic may be called as "twohypo-low-lyings clamping one heave". It is important to enhance studying works in Denan sag. This sag has goodsource-reservoir-cap rocks and traping conditions. Oil/gas show is rich. There even attainedindustry oil-stream in the D1 drill hole in 1990. But, Denan sag is so complex that there hasn'timportant breakthrough in oil exploration by far. So, hard works should be done in the region. Researching petroleum migration could help us to understand oil how to move, whichpathes and directiones to pass through and where to store. Moreover, it would provide moreaccurate,effective informationes for the petroleum exploration. Based on the microscopicanalysis technology(fluid inclusion) and predecessor's research results, the paper discussed thethermodynamics and dynamics mechanism of hydrocarbon migration, and restored the migrationtimes, channels and directions, finally pointed out the oil/gas advantageous accumulation areas. Through the systemic research, the paper achieves the following results and conclusions: 1. In the area there have a great deal of fluid inclusions in authigenic minerals. According tothe physical phases, they can be divided into six species: single phase inclusion, liquid-richinclusion, gas-rich inclusion, multi-phases with liquid CO2 fluid inclusion, liquid hydrocarboninclusion and gaseous hydrocarbon inclusion. The relative abundance of organic inclusion is4~7%. They always exist in sandstone or marlite sections of Es1,Es3,Es4,Ek and Pz, especiallyin Ek of D6 well and Pz of DG2 well, where the abundance can reach 70%. 2. The paper has a detailed study on organic inclusions petrography and thermodynamicscharacteristics. Ⅴ type inclusions mainly distributes in Tertiary. Their homogeneoustemperatures have three peak sections, 50~70℃,100~140℃,160~170℃,and the middle peakis the highest; The quantity of gaseous hydrocarbon inclusions(Ⅵ) is less, which relativelyconcentrate in Paleozoic group general with carbon dioxide inclusions. Their homogeneoustemperatures are higher, about 180～280℃. 3. The analysis of fluid inclusion composition indicated that the fluid in Tertiary system wascomposed of immature and low mature liquid hydrocarbon with high sulfur, and in Paleozoic wasmature or over mature gaseous hydrocarbon. Considering the analysis of the paleosalinity, thepaper concluded the ancient aqueous medium was rich Cl-, w (NaCl) >4%. The pressure changesalong with the depth were irregular, however, high pressures always happened with abundantorganic inclusions, which could indicate when the hydrocarbon fluid was massively discharging,the pressure broke out and released. 4. The microthermometry and ingredient datum from fluid inclusions in each of thediagenesis stages were used to determine the temperatures,pressures,depths and aqueousmedium characteristics of fluid migrations. Synthesizing the diagenesis and fluid inclusioncharacteristics, the author found there were four times of big fluid activities. The first lowtemperature fluid activity mainly occurred in the compaction and cementation stages; The secondmid-low temperature fluid containing a little hydrocarbon was in the recrystallization and theearly structure filling periods; the third mid-high temperature liquid hydrocarbon fluid activityhappened in the middle-late structure activity stages, usually moving in the Tertiary strata; thelast high temperature gaseous hydrocarbon and carbon dioxide stream occurred in the laterstructure activity period, often flowing up from Paleozo...