Taking the Lower Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin as an example,the influences of the burial process in a foreland basin on the diagenesis and the development of high-quality reservoirs of deep and ultra-deep clastic rocks were investigated using thin section,scanning electron microscope,electron probe,stable isotopic composition and fluid inclusion data.The Qingshuihe Formation went through four burial stages of slow shallow burial,tectonic uplift,progressive deep burial and rapid deep burial successively.The stages of slow shallow burial and tectonic uplift not only can alleviate the mechanical compaction of grains,but also can maintain an open diagenetic system in the reservoirs for a long time,which promotes the dissolution of soluble components by meteoric freshwater and inhibits the precipitation of dissolution products in the reservoirs.The late rapid deep burial process contributed to the development of fluid overpressure,which effectively inhibits the destruction of primary pores by compaction and cementation.The fluid overpressure promotes the development of microfractures in the reservoir,which enhances the dissolution effect of organic acids.Based on the quantitative reconstruction of porosity evolution history,it is found that the long-term slow shallow burial and tectonic uplift processes make the greatest contribution to the development of deep-ultra-deep high-quality clastic rock reservoirs,followed by the late rapid deep burial process,and the progressive deep burial process has little contribution.

Constrained by the geological burial history of Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin, the diagenetic physical simulation experiment was carried out with the low-mature sandstone samples taken from the outcrop area. Then, coupling with the regional geological data, the reformation of reservoirs with different diagenetic intensities by microfractures and the significance of microfractures for development of high-quality reservoirs were discussed. The results show that the large-scale microfractures were formed in the stage of late rapid deep burial, roughly equivalent to the period when organic acids were filled. The microfractures created good conditions for migration of oil and gas in deep and ultra-deep clastic rocks, and also enabled the transport of organic acids to the reservoirs for ensuing the late continuous dissolution of cements and particles. The existence of matrix pores and microfractures in the reservoirs before the rapid deep burial determined how the microfractures formed during rapid deep burial improved the reservoir quality. If matrix pores and microfractures were more developed and the cementation degree was lower before the rapid deep burial, the microfractures would be more developed and the dissolution degree would be higher during the late rapid deep burial, and so the reservoir quality would be improved more greatly, which can increase the reservoir permeability by up to 55%. If cementation was very strong, but matrix pores were not developed and microfractures existed locally before the rapid deep burial, the microfractures would also be more developed during the late rapid deep burial, which can increase the reservoir permeability by 43%. If cementation was strong, matrix pores were absent, and microfractures were not developed, limited microfractures would be formed during the late rapid deep burial, which can increase the reservoir permeability by only 16%. Formation of large-scale microfractures during late rapid deep burial and promotion of such microfractures to the dissolution of organic acids are considered as key diagenetic factors for the development of deep and ultra-deep high-quality reservoirs.

以准噶尔盆地南缘四棵树凹陷下白垩统清水河组辫状河三角洲碎屑岩为研究对象,采用岩心观察、岩石薄片观察、扫描电镜和压汞实验等方法分析成岩作用特征;根据岩心成岩相测井响应关系,进行测井成岩相识别和储层评价.结果表明:四棵树凹陷清水河组主要发育长石岩屑砂岩和岩屑砂岩,储集空间类型丰富,非均质性较强,既存在粗孔喉、连通性较好的粒间孔隙,为储层主要储集空间类型,也存在细微孔喉、低渗透率的粒内溶孔和粒间溶孔,属于特低孔—特低渗、超低孔—超低渗储层.研究区识别4类成岩相,其中强压实致密相多见蚀变凝灰质充填,发育于河道边缘薄层砂岩;钙质(铁泥质)致密胶结相集中发育于河道主体厚层砂岩的顶底部,孔喉结构较差;凝灰质致密充填相发育于分布最广的弱动力环境,粒间杂基多而物性差;欠压实溶蚀相主要发育于水下分流河道,排替压力较低、孔隙结构最好.自然伽马、声波时差、密度、中子测井及电阻率多元统计结果平均判识率达80.6％.该结果为取心井测井成岩相的研究和优质储层发育规律的认识、有利储层发育带的评价和优选提供支持.