松辽盆地古龙页岩油层顶底板断层封闭性及油气聚集有利区优选

Roof and floor faults seal of Gulong shale oil reservoir in Songliao Basin and optimization of favorable areas for oil and gas accumulation

松辽盆地古龙页岩油勘探取得了重大突破,但在大面积连续稳定分布的页岩油层中科学高效地寻找油气成藏有利区,断层的影响及作用不可忽视。古龙页岩油层顶底板断层两侧地层以泥岩和页岩为主,油气难以穿过断层进行大规模的侧向运移,因此从断层分类、分布及应力场入手,通过计算不同断层在烃源岩排烃期和现今的滑动稳定性来分析断层的垂向封闭性。结果表明:在没有构造运动发生时期多数断层在垂向上基本都是封闭的,在构造活动期间断层封闭性与构造应力的大小和方向密切相关;顶底板断层多数呈近南北向展布,与现今区域最大主应力方向近于垂直,垂向封闭性较好,生成的油气不易排出;在大规模排烃的明水组沉积末期,区域最大主应力方向与断裂走向近于平行,约半数断层不稳定,垂向封闭性较差,油气沿断层运移到上部的葡萄花、萨尔图油层或者下部的扶杨油层;现今相对稳定的断裂带附近和距离断裂带较远的区域受断层影响较小,有利于页岩油的保存,稳定性差的断裂带附近不利于页岩油的保存;排烃期稳定性好的断裂带附近不利于油气的排出,是有利目标区,排烃期稳定性差的断裂带附近部分油气已经排出,不是有利目标区。断裂和伴生的裂缝能提升页岩油层的储集物性,有利于后期开发建产。研究成果可为下一步页岩油勘探和开发提供依据。

Great achievement has been obtained in Gulong shale oil exploration in Songliao Basin,but the influence and role of faults cannot be ignored in finding favorable oil and gas accumulation areas scientifically and efficiently in large-area continuous and stable shale reservoirs.The strata on both sides of the roof and floor faults of Gulong shale reservoir are mainly mudstone and shale,preventing large scale lateral migration of oil and gas through the faults.Therefore,starting from faults classification,distribution and stress field,vertical sealing of faults are analyzed by calculating slip stability of different faults in hydrocarbon expulsion period of source rocks and at present.The results shows that most faults were generally sealed vertically in the period with no tectonic movement,and fault seal was closely related to the magnitude and direction of tectonic stress during tectonic movement.Most of the roof and floor faults distribute in near south-north direction,which is nearly perpendicular to the direction of current maximum regional principal stress,with high-quality vertical seal,and generated oil and gas were not easy to be discharged.At the end of Mingshui Formation sedimentation with large-scale hydrocarbon expulsion,the direction of maximum regional principal stress was nearly parallel to faults strike,half of the faults were unstable,with poor vertical seal,and oil and gas migrated along the faults upwards to Putaohua and Saertu reserviors and downwards to Fuyang reservoirs.At present,the areas near relatively stable fault zones and far away from fault zones are less affected by faults,being conducive to shale oil preservation,and the areas near fault zones with poor stability are not conducive to shale oil preservation.The areas near fault zones with good stability in hydrocarbon expulsion period are not conducive to oil and gas discharging,being favorable target areas,while part of oil and gas near fault zones with poor stability in hydrocarbon expulsion period were discharged,being not favorable target areas.Faults and associated fractures can improve physical properties of shale reservoir,favorable for later development and production.The research provides evidence for further exploration and development of shale oil.