松辽盆地徐家围子断陷沙河子组储层特征及控制因素

徐家围子断陷沙河子组是松辽盆地北部近期天然气勘探的主要目标,这类致密砂砾岩气层的储层特征及控制因素研究是首要的。通过分析其白垩系早期拉张构造背景条件下形成的一套断陷沉积,纵向上可划分为4个三级层序,各层序在断陷湖盆陡坡带和缓坡带发育扇三角洲和辫状河三角洲沉积。研究表明其储层主要为砂砾岩和含砾粗砂岩等粗碎屑岩。沙河子组储层孔隙包括原生粒间孔和次生孔隙,孔隙度主要分布在2%～8%,渗透率多小于0. 1×10^-3μm^2,为致密储层。沙河子组储层发育的控制因素包括埋深、沉积相带、岩石类型和次生成岩作用,埋藏浅的扇三角洲(辫状河三角洲)前缘、平原相砂砾岩储层物性好,含火山碎屑物质的砂岩、砂砾岩易于形成溶蚀孔隙,改善储集性能。徐家围子断陷沙河子组有利储层主要位于埋深小于4 000 m的安达东、西两侧的扇三角洲前缘、平原区和徐东、徐西的构造高部位扇体发育区,埋藏较浅的安达中部滨浅湖相和埋藏较深的徐东、徐西斜坡扇体发育区也是较有利的储层发育区。

Reservoir characteristics and controlling factors of Shahezi Formation in Xujiaweizi Fault Depression,Songliao Basin

The Shahezi Formation in the Xujiaweizi Fault Depression is the main target for recent natural gas exploration in the northern Songliao Basin.It is of great significance to study the reservoir characteristics and controlling factors of such tight glutenite gas reservoir.The deposits in the fault depression formed in an early Cretaceous extensional tectonic environment,can be divided into four third-order sequences vertically,each of which develops depositions of fandelta and braided delta in the steep and gentle slope zones of the rifted lacustrine basin.The reservoir isdominated by coarse clastic rocks such as glutenites and pebbly coarse sandstones.The reservoir pores of the Shahezi Formation consist of primary intergranular pores and secondary pores,with porosity mainly in the range of 2% to 8% and with permeability usually less than 0.1×10^-3μm²,indicating a tight reservoir.The controlling factors for reservoir development in the Shahezi Formation include burial depth,sedimentary facies belt,rock type and epigenesis.The fan delta front(braided delta)with shallow depth and glutenite reservoir of plain faciesare characteristic of good reservoir quality,while the sandstones and glutenites with pyroclastic materials,tend to form dissolution pores and improve the reservoir performance.The favorable reservoirs of the Shahezi Formation in the Xujiaweizi Fault Depression are mainly located in the fan-delta front and the plain area with a burial depth less than 4 000 m at the east and west sides of Anda,as well as in the higher part of fan development zone of Xudong and Xuxi areas.The shore-shallow lake facies with shallow depth in central Anda and the Xudong and Xuxi slope fan development zones with deep depth are also favorable zones for reservoir development.