松辽盆地齐家地区高台子油层致密砂岩油成藏机理

Accumulation mechanism of tight sandstone oil in Gaotaizi reservoir in Qijia area,Songliao Basin

致密油已成为中国含油气盆地勘探重要领域。以松辽盆地齐家地区高台子油层致密油为研究对象,利用岩心、薄片、流体包裹体、地球化学和试油等资料,分析了致密油藏特征,明确了致密油成藏机理。研究表明:高台子油层储层主要发育残余粒间孔和长石溶孔,孔隙度平均为9.17%,渗透率平均为0.45×10-3μm2,平面上北部孔隙度超过12%,中、南部多数小于12%,属于致密储层;致密油藏类型主要为断层、岩性-断层和岩性油藏,呈现平面叠加连片、纵向多层叠置的准连续型分布特征,油藏受砂体展布、断层和储集物性控制,不受构造高点控制;青山口组一段(青一段)和二段烃源岩厚度大,总有机碳含量分别为2.47%和1.60%,且处于生油高峰期,属于优质烃源岩;致密油成藏期次为2期3幕,分别为嫩江组沉积末期和明水组沉积期;致密油运移通道为未断穿青山口组的断层、裂缝和砂体;嫩江组沉积末期,高台子油层顶面埋深为800~1400 m,其所对应的古孔隙度约21%~15%,烃源岩生烃作用所产生的最大剩余压力约10 MPa,仅在生烃中心形成局部油藏;明水组沉积末期,高台子油层顶面埋深为1600~2200 m,对应的古孔隙度约13%~7%,储层处于致密状态,烃源岩生烃作用产生的最大剩余压力可达25 MPa,形成大面积分布的致密油藏;致密油成藏模式为下生上储-源储间互双源供烃型准连续成藏模式。

Tight oil has become an important exploration field in China’s petroliferous basins. The study focuses on the tight oil of Gaotaizi reservoir of Qijia area in the Songliao Basin. An array of data obtained from core,thin section,and fluid inclusion observation,geochemical analysis and production test,are applied to analyze the characteristics of the Gaotaizi tight sandstone reservoir,and clarify the accumulation mechanism of tight oil. The results show that the pore space of Gaotaizi reservoir is dominated by residual intergranular pores and feldspathic dissolved pores,with a mean porosity of 9. 17%and a mean permeability of 0. 45×10-3μm2. On map view,the porosity of Gaotaizi sandstone reservoir in the northern part of Qijia area is mostly over 12%,while that in the sorth-central area is mostly less than12%,thus belonging to tight reservoir. The tight reservoirs are mainly of faulted,lithologic-faulted and lithologic types in quasi-continuous distribution and are laterally superimposed and connected and vertically overlapped. They are controlled by sand body distribution,faults and reservoir physical properties,instead of structural highs. The source rocks of the 1 stand 2 ndmembers of Qingshankou Formation(Qing 1 and Qing 2 members)are of high quality at the peak of oil generation,featuring relatively large thickness and a TOC content of 2. 47%and 1. 6%,respectively. The tight oil accumulation occurred in 3 episodes of 2 stages,that is the late Nenjiang period and Mingshui period. The faults which do not cut through the Qingshankou Formation,fractures and sand bodies provide pathways for tight oil migration.The burial depth of the top surface of the Gaotaizi reservoir was 800-1 400 m at the end of the Nenjiang Formation deposition,corresponding to a palaeo-porosity of about 21%-15%,and the maximum residual pressure was about 10 MPa,resulting in only conventional reservoir in the center. While its burial depth was 1 600-2 200 m at the end of Mingshui Formation deposition,corresponding to a palaeo-porosity of about 13%-7%,and the maximum residual pressure was over 25 MPa,resulting in tight oil reservoir in wide distribution. The accumulation model of tight oil therein can be concluded as a quasi-continuous type of dual sourced hydrocarbon charging,featuring an lower source rock-upper reservoir assemblage and source-reservoir alternating configuration.