Research On Accumulation Dynamics Of Fuyu Oil Reservoir In Sanzhao Sag, Songliao Basin

Fuyu oil reservoir in Sanzhao Sag is a typical tight reservoir, which has the relationship of "up-source and down-reservoir" with the hydrocarbon source rocks in Member I of Qingshankou formation(K1qn1). In order to make an accurate understanding of dynamic environment of tight oil accumulation, the accumulation process of Fuyu reservoir was analyzed by the simulation of burial history, thermal history, sedimentation history,hydrocarbon generation and expulsion history. In addition, based on the overpressure formation mechanism analyzed by 6 kinds of methods, the accumulation characteristics of dynamic distribution during the critical accumulation period was reconstructed quantitatively.Combined with the distribution of reservoir property, fault and the accumulation dynamic, the oil primary and secondary migration distances was calculated. Based on the study mentioned above, the accumulation patterns in Sanzhao Sag and its adjacent area were summarized.Specific understanding is as follows:Based on the the correction for organic matter content, it was determined that the overpressure in hydrocarbon source rocks of K1qn1 was caused by disequilibrium compaction early,and was adjusted by the overpressure from late hydrocarbon generation.Combined with the burial history analysis, this paper considers, K1qn1 in Sanzhao Sag had experienced the pressure evolution process of "overpressure generated from disequilibrium compaction ?pressure slightly released by tectonic uplift - pressurization by hydrocarbon generation -pressure sharply released by tectonic uplift"; K1qn1 in Changyuan area had experienced the pressure evolution process of "overpressure generated from disequilibrium compaction -pressure sharply released by tectonic uplift - pressurization by hydrocarbon generation -pressure slightly released and adjusted by tectonic uplift".According to the hydrocarbon generation history, it was considered that the hydrocarbon generation intensity of K1qn1 reached maximum value at the end of Mingshui formation sedimentary stage. Combining with pressure evolution history and fault distribution, the calculation resulted that the vertical maximum distance of oil migration along faults is 1860 m,which reflected the adequate accumulation dynamic source. Based on the threshold pressure gradient, the lateral migration distance was calculated. The results showed that the maximum distance of lateral migration was 1600 m in the hydrocarbon generation center at the end of Mingshui formation sedimentary stage.Integration of the feature of the pressure, migration, tectonic and reservoir physical property at the critical accumulation period, 4 kinds of quasi-continuous accumulation patterns of tight oil was constructed:?Sag zone: "up-source and down-reservoir - overpressure drive-vertical migration along the fault";? Slope area: "up-source and down-reservoir -overpressure drive - vertical migration along the fault + lateral migration along the sand";?Changyuan area: "up-source and down-reservoir - buoyancy and overpressure drive - vertical migration along the fault + lateral migration along the sand";? Chaoyanggou area:"up-source and down-reservoir - overpressure and buoyancy drive - vertical migration along the fault + lateral migration along the sand".