海拉尔盆地中部断陷带下白垩统南屯组致密储层特征及有利区预测

Tight reservoir characteristics and favorable areas prediction of Lower Cretaceous Nantun Formation in central fault depression zone of Hailar Basin

综合运用岩心分析、铸体薄片、高压压汞等资料,对海拉尔盆地中部断陷带下白垩统南屯组储层特征及其主控因素开展了详细研究,并对有利区进行了定量综合评价。研究结果表明:(1)海拉尔盆地中部断陷带南屯组岩石类型主要为岩屑砂岩和长石岩屑砂岩,储层孔隙度小于12%的样品数占总样品数的70.2%,渗透率小于1 mD的样品数占总样品数的66.3%,属于致密砂岩储层,储层储集空间主要为少量原生孔隙和大量次生溶蚀孔隙。(2)沉积相控制了研究区储层物性在空间上的总体分布规律,南屯组最有利的沉积相带是辫状河三角洲前缘和扇三角洲前缘亚相;压实作用对储层具有减孔效应,溶蚀作用普遍发育,形成了大量粒间和粒内溶孔,对储集性具有一定改善作用。(3)盆地中部断陷带发育缓坡断阶构造带、陡坡断阶构造带和洼槽带3种构造带,其中缓坡断阶构造带和陡坡断阶构造带为主要的油气聚集区带,其断裂的大量发育均早于或同期于烃源岩大量排烃阶段,为油气运移提供了通道。(4)将“沉积相-孔隙度-储层厚度-砂地比-埋藏深度”五要素进行叠合,定量评价有利储层发育区,其中Ⅰ类、Ⅱ类优质储层主要分布在盆地中部断陷带的缓坡断阶构造带和陡坡断阶构造带。

The data of core analysis,cast thin sections and high-pressure mercury injection were used to study the reservoir characteristics and main controlling factors of Lower Cretaceous Nantun Formation in central fault depression zone of Hailar Basin,and the favorable areas were quantitatively and comprehensively evaluated.The results show that:(1)The rock types of Nantun Formation in in central fault depression zone of Hailar Basin are mainly lithic sandstone and feldspathic lithic sandstone,with reservoir porosity less than 12%accounting for 70.2%and permeability less than 1 mD accounting for 66.3%.It belongs to the category of tight sandstone reser‐voir,and the reservoir space is a small number of primary pores and a large number of secondary pores.(2)The sedimentary facies control the overall spatial distribution of reservoir properties in the study area.The most favor‐able sedimentary facies zones of Nantun Formation are braided river delta front and fan delta front subfacies.Compaction has a pore reducing effect on the reservoir,and dissolution is generally developed,forming a large number of intergranular and intragranular dissolved pores,which has a certain improvement effect on the reser‐voir properties.(3)There are three types of structural belts developed in the central fault depression zone of the basin:gentle slope fault terrace structural belt,steep slope fault terrace structural belt,and trough belt.Among them,the gentle slope fault terrace structural belt and steep slope fault terrace structural belt are the main oil and gas accumulation zones,and the development of their faults is earlier than or contemporaneous with a large number of hydrocarbon expulsion stages of the source rocks,providing channels for oil and gas migration.(4)Five elements of sedimentary facies,porosity,reservoir thickness,sand to stratum ratio and burial depth were superimposed to quantitatively evaluate the favorable reservoir development areas.Among them,typeⅠand typeⅡhigh-quality reservoirs are mainly distributed in the gentle slope fault terrace structural belt and steep slope fault terrace struc‐tural belt in the central fault depression zone of the basin.