渤海湾盆地歧口凹陷中深层天然气成藏条件与资源潜力

Natural gas formation conditions and resource potential in mid-deep strata of the Qikou Sag,Bohai Bay Basin

近年来随着勘探目标向中深层拓展,在渤海湾盆地歧口凹陷不仅发现大规模的石油资源,同时发现700多亿立方米的天然气资源。深层烃源岩热演化与储集层物性特征的差异,决定了深层常规、非常规气藏并存,且以4 700m深度为界,该深度以下主体为致密砂岩气。利用成因法、类比法等方法综合计算,歧口凹陷古近系常规天然气资源规模超过3 500×10~8 m^3,主要分布在板桥次凹,致密砂岩气资源量为1 760×10~8 m^3,主要分布在歧北次凹中深层。通过天然气成藏条件综合评价,进一步揭示了深层优质烃源岩、高演化程度和大规模砂体三大因素有利于天然气规模富集,是深层烃类资源的主要赋存状态。板桥斜坡深层、歧北斜坡深层为深层气勘探的有利目标区,尤其是处于气源中心区、具有一定构造背景、砂体发育的沙二段是深层气现阶段勘探最现实的领域。

In recent years, as exploration targets have expanded to the mid-deep strata, large-scale oil re- sources have been discovered in the Qikou Sag of the Bohai Bay Basin,and more than 70 billion cubic me- ters of natural gas resources were discovered as well.The difference between the thermal evolution of deep source rocks and the physical properties of reservoirs determine the coexistence of conventional gas reser- voirs and unconventional gas reservoirs in deep strata,and it is bounded by a depth of 4 700m.The main body below this depth is tight sandstone gas. Using the method of generative and analogy, the Paleogene conventional natural gas resources of the Qikou Sag are more than 350 billion cubic meters,mainly distrib- uted in the Banqiao sub-sag,and the tight sandstone gas resources are 176 billion cubic meters, mainly dis- tributed in the mid-deep strata of Qibei sub-sag.Through the comprehensive evaluation of natural gas accu- mulation conditions, it further reveals that the three factors of deep high-quality source rock, high evolution and large-scale sand body are conducive to the enrichment of natural gas, which is the main occurrence state of deep hydrocarbon resources.The deep strata of Banqiao and Qibei Slopes are favorable target areas for deep gas exploration,especially in the central area of gas source,in the second member of Shagejie Forma- tion with a certain tectonic setting and sand body development, which is the most realistic area for deep gas exploration.