前陆冲断带深层储集层非均质性及油气差异聚集模式——以准噶尔盆地南缘西段白垩系清水河组碎屑岩储集层为例

Heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in foreland thrust belts:A case study of deep Cretaceous Qingshuihe Formation clastic reservoirs in southern Junggar Basin,NW China

基于钻井、测井、岩心及实验数据和油气生产资料,对准噶尔盆地南缘前陆冲断带西段深层白垩系清水河组储集层非均质性及其油气差异聚集模式进行研究。结果表明:(1)储集层以叠置连片的砾岩、砂砾岩及砂岩为特征,塑性岩屑含量高,储集空间以粒间孔为主,整体致密,其中砂砾岩物性最优;(2)较短的深埋时限匹配较低的古地温梯度和地层超压使得储集层整体成岩强度较弱,而砂砾岩具有相对更低的早期碳酸盐胶结及压实率和更高的溶蚀增孔;(3)背斜特殊的应力-应变机制使得转折端顶部储集层可较两翼宏观裂缝改造程度更大,且超压使得裂缝处于开启状态;(4)砂砾岩相对含油饱和度最高,而冲断带深层发育典型背斜油气藏,但整体表现为“大圈闭,小油藏”的特点;(5)背斜转折端顶部砂砾岩相较于两翼具有更优越的储集性能、更低的地应力大小及较高的构造位置,使得内部油气最为富集而成为高产油气层,而裂缝指数级递减使得两翼储集层难以富集成藏,但背斜缓翼相对陡翼油气平面延伸范围更大。

Using the data of drilling,logging,core,experiments and production,the heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in Cretaceous Qingshuihe Formation(K1q)in the western section of the foreland thrust belt in southern Junggar Basin are investigated.The target reservoirs are characterized by superimposition of conglomerates,sandy conglomerates and sandstones,with high content of plastic clasts.The reservoir space is mainly composed of intergranular pores.The reservoirs are overall tight,and the sandy conglomerate has the best physical properties.The coupling of short deep burial period with low paleotemperature gradient and formation overpressure led to the relatively weak diagenetic strength of the reservoirs.Specifically,the sandy conglomerates show relatively low carbonate cementation,low compaction rate and high dissolution porosity.The special stress-strain mechanism of the anticline makes the reservoirs at the top of the anticline turning point more reformed by fractures than those at the limbs,and the formation overpressure makes the fractures in open state.Moreover,the sandy conglomerates have the highest oil saturation.Typical anticline reservoirs are developed in deep part of the thrust belt,but characterized by"big trap with small reservoir".Significantly,the sandy conglomerates at the top of anticline turning point have better quality,lower in-situ stress and higher structural position than those at the limbs,with the internal hydrocarbons most enriched,making them high-yield oil/gas layers.The exponential decline of fractures makes hydrocarbon accumulation difficult in the reservoirs at the limbs.Nonetheless,plane hydrocarbon distribution is more extensive at the gentle limb than the steep limb.