油气垂向和侧向倒灌运移条件及其聚集规律的差异性

Conditions of oil-gas downward migration in vertical and lateral and their differences in accumulation laws

以松辽盆地三肇凹陷扶杨油层和渤海湾盆地南堡凹陷中浅层为例,对油气垂向和侧向倒灌运移条件及聚集规律的差异性进行研究.在系统阐述油气侧向倒灌运移所需条件和聚集规律的基础上,从油气运移所需动力条件和聚集分布部位上探讨了二者的差异性.研究结果表明：油气垂向和侧向倒灌运移所需条件不同,油气垂向倒灌运移所需条件是上覆源岩具有超压和发育输导断裂,三肇凹陷青一段源岩古超压约为5 MPa,大于所有遇到的各种阻力之和,且发育有大量SN向展布、断裂密度为0.5~1.8条/km的输导断裂;而油气侧向倒灌运移条件是受到上覆区域性盖层的阻挡,油气不能通过断裂穿过区域性盖层向上运移.垂向和侧向倒灌运移油气聚集规律也不同,垂向倒灌运移油气聚集从上至下逐渐减小,主要聚集在顶部储层中,而侧向倒灌运移油气则主要聚集在区域性盖层之下高的砂地比地层中;垂向倒灌运移油气主要聚集在输导断裂下盘,而侧向倒灌运移油气则主要聚集在输导断裂上盘.

By analyzing the oil-gas accumulation in Fuyang oil layer of Sanzhao depression in Songliao basin and intermediate-shallow strata of Nanpu depression in Bohaiwan basin, the conditions of oil-gas downward migration in vertical and lateral and their accumulation laws were studied in this paper. Based on systematical description on conditions and accumulation laws of oil-gas downward migration in lateral, the differences of the required dynamic condi- tions and accumulation locations of migrations in vertical and lateral were discussed. The results indicate that the required conditions of migration along the two directions are different. Oil-gas downward migration in vertical needs overpressure in overlying source rock and transporting faults the first member of Qingshankou formation of Sanzhao depression bears palaeooverpressure of about 5 MPa, which is greater than the sum of all kinds of resistance, and develops large amounts of SN-trend transporting faults, with fracture density of about 0.5-1.8 fault per kilometer. In contrast, the migration in lateral is sealed by overlying regional caprock, and the oil-gas cannot get through the regional caprock and migrate upward through faults. The accumulation laws are different either. Oil-gas downward migration in vertical gradually reduced from top to bottom, and mainly accumulated at the top of the reservoir, while the migration in lateral mainly distributed in strata with high sandstone stratum ratio under the regional caprock. The downward migrated oil-gas in vertical and lateral respectively accumulated in footwalls and hanging walls of transporting faults.