吐哈盆地台北凹陷低饱和度油藏特征及其成因

Characteristics and Genesis of Low Oil⁃Saturation Reservoirs in Taibei Sag,Tuha Basin

吐哈盆地台北凹陷水西沟群普遍发育低饱和度油藏,平面上多集中在台北凹陷正向构造,纵向上主要赋存于西山窑组和三工河组。研究区低饱和度油藏基本特征为含油饱和度低、储集层物性差、自然产能低、储集层改造后高产、长期油水同出。为了解该类油藏成因,基于储集层、构造、成藏演化与含油饱和度之间的关系开展研究。结果表明,储集层和构造是影响油藏含油饱和度的主要因素,一是压实减孔、细孔微喉造成油气充注不彻底,导致低含油饱和度;二是夹层或遮挡层的存在,油气藏被分割,阻碍了油气纵向调整;三是低幅度构造成藏动力不足,影响含油饱和度;四是后期构造活动对古油藏的调整破坏导致含油饱和度低。综合分析认为,台北凹陷水西沟群低饱和度油藏剩余资源量大,是吐哈盆地油气勘探的重要接替领域,储集层甜点与继承性正向构造叠合区,是寻找相对高含油饱和度油藏的有利区。

Low oil⁃saturation reservoirs are widely developed in the Shuixigou group in the Taibei sag of the Tuha basin,which are laterally concentrated in the positive structures in the sag,and vertically in the Xishanyao formation and Sangonghe formation.The oil reservoirs in the study area have low oil saturation and poor physical properties,so the natural productivity is low.Although the production is high after reservoir stimulation,both oil and water are produced for a long time.In order to understand the genesis of such oil reservoirs,the relation⁃ships among reservoir,structure,reservoir evolution and oil saturation were studied.The results show that the reservoir and structure are primary factors resulting in the low oil saturation.The reasons are as follows:the first is that the oil displacement by water is not complete due to compaction and pore reduction,fine pores and micro throats;the second is the existence of interlayers or barriers,which separate the oil layers and block the vertical migration of oil and gas;the third is that the low⁃relief structure provides an insufficient reservoir forming dynamics which will bring impacts on oil saturation;and the fourth is that late tectonic activities destruct the ancient oil reservoirs.Compre⁃hensive analysis shows that the low oil⁃saturation reservoirs in the Shuixigou group in the Taibei sag have a large amount of remaining hy⁃drocarbon resources,which are important replaceable targets for oil and gas exploration in the Tuha basin.The overlapping areas of reser⁃voir sweet spots and inherited positive structures are favorable for looking for the reservoirs with higher oil saturation.