Abstract: To make clarify the geological characteristics and resource potentials of tight gas in northern Songliao Basin, the classification and optimization of favorable exploration areas for tight gas were carried out based on comprehensively using the seismic, coal, geological and geochemical data and analyzing the hydrocarbon accumulation conditions in Shahezi Formation, including tectonic evolution, sedimentary system, source rock, favorable reservoir and abnormal pressure. The results show as follows. (1)The tight gas is mainly concentrated in Shahezi Formation in the deep fault depressions. Influenced by paleo-geomorphology and fault activity, fan delta and braided river delta sediments were formed on the steeps and the gentle slopes of deep fault depressions, and huge pebbly sandstone was deposited, which is the main gas-bearing horizon of tight gas. (2)The coal rock and dark mudstone have high organic matter abundance and are in the high mature-over-mature stage, which provides sufficient material guarantee for the formation of tight gas. Under the joint control of sedimentation and dissolution, high quality reservoirs with intragranular and intergranular solution pores of feldspar as the main reservoir space are developed in tight sandstone, which is the sweet spots for tight gas exploration. Hydrocarbon generation from organic matter results in the 29 MPa to 45 MPa pressurization, forming a large-scale continuous overpressure storage chamber in the middle of the depression, which is the main driving force for tight gas charging. (3)Homogenization temperature simulation of hydrocarbon-bearing fluid inclusions and burial history of strata show that the accumulation time of Shahezi Formation tight gas lasted from the end of Qingshankou Formation to the sedimentary period of Nenjiang Formation (91-72 Ma), and there were two accumulation processes in the end of Qingshankou Formation and the Nenjiang Formation. (4)Based on the sedimentary system, reservoir thickness and physical property conditions, the tight gas is divided into two favorable exploration types, i.e., thick-layer and interlayer. Moreover, four favorable exploration zones have been identified, including Anda, Xuxi, Xudong and Xunan, and the amount of tight gas resources is estimated to be about 4 224.10×10⁸m³.

Key words: resource potential, fault basin, tight gas, Shahezi Formation, Songliao Basin

摘要： 为明确松辽盆地北部致密气藏的地质特征和资源潜力,综合地震、岩心、地质和地球化学特征等多种资料,基于沙河子组的构造演化、沉积体系、烃源岩、有利储层和异常压力等成藏条件分析,开展了沙河子组致密气有利勘探类型划分和有利勘探区优选。研究结果表明:①松辽盆地北部致密气主要集中在深部断陷群中的沙河子组,受古地貌和断裂活动影响,深部断陷的陡坡带和缓坡带分别发育扇三角洲和辫状河三角洲沉积,沉积了巨厚的含砾砂岩,是致密气的主要含气层位。②沙河子组煤岩和暗色泥岩的有机质丰度高,处于高成熟—过成熟阶段,为致密气的形成提供了充足的物质保障;在"沉积＋溶蚀"双重作用控制下,致密砂岩以长石粒内溶孔和粒间溶孔为主要储集空间,形成优质储层,是致密气勘探的"甜点区";有机质生烃造成了29~45 MPa的增压,在凹陷中部形成大范围、连续的超压封存箱,是致密气充注的主要动力。③含烃流体包裹体的均一温度和地层的埋藏史模拟分析表明,沙河子组致密气的成藏期在青山口组沉积末期至嫩江组沉积期(91~72 Ma),存在青山口组沉积末期和嫩江组沉积期2次成藏过程。④以沉积体系、储层厚度和物性条件为关键依据,将致密气储层划分为厚层型和互层型2种有利勘探类型,并在盆地北部的徐家围子断陷中优选出安达、徐西、徐东和徐南4个勘探区,作为近期致密气勘探的突破方向,估算致密气资源量为4 224.10×10⁸m³。

关键词: 资源潜力, 断陷盆地, 致密气, 沙河子组, 松辽盆地