查干凹陷早白垩世碎屑岩储层成岩作用及孔隙演化

在对大量薄片和岩心观察分析基础上,结合扫描电镜和全岩分析、 X衍射粘土分析、 包裹体测温等手段,对查干凹陷碎屑岩储层的成岩作用和孔隙演化进行了研究。结果表明: 研究区碎屑岩储层主要为低成分成熟度、 低结构成熟度的长石岩屑砂岩,成岩作用呈现“强压实、 强胶结、 弱交代、 弱溶蚀“的“两强两弱”特征;成岩阶段主要处于中成岩A期,局部达中成岩B期至晚成岩期。两期胶结主要发生在苏二早期和乌兰苏海时期,中浅层（<2 500 m）较低孔隙度主要由于强压实和早期致密胶结所致;较高孔隙度是由于原生孔隙保存较好,长石及碳酸盐胶结物的溶蚀作用导致孔隙度增大。深层碎屑岩储层（>2 500 m）较低孔隙度除压实作用外,碳酸盐致密胶结是主因;较高孔隙度则为早期酸性溶蚀叠加晚期碱性溶蚀产生次生孔隙为主。晚期碱性溶蚀发生在油气充注之后,为无效溶孔。

Diagenesis and evolution of pores in elastic rock reservoir of Early Cretaceous in Chagan sag

On the basis of the analysis of a number of rock slices and drill cores observation, combined with the means of scanning electron microscopy, whole-rock analysis, X-ray diffraction clay analysis and inclusion thermometry, study has been done about the diagensis of clastic rock reservoir and pore evolution in Chagan depression. The findings show that the reservoir is mainly composed of lithic arkoses with low contents maturity and low structure maturity. And its diagenesis presents the "two strong-two weak" diagenetic characteristics: strong compaction, strong cementation, weak metasomasis, and weak dissolution; the diagenetic stage is in the diagenetic A period, and in some areas, the diagenetic stage is up to the the diagenetic B to late diagenetic. The cement of two stages mainly occurred in the early K₁s₂ and K₁w period. In the middle-shallow layer(<2 500 m)the lower porosity is mainly caused by the strong compaction and early cementation. The higher porosity is caused by the better preservation of primary porosity, and at the same time the dissolution of feldspar and carbonate cements widens porosity. In the deep clastic reservoirs(>2 500 m)except the compaction, carbonate cementation is the main reason for lower porosity; the higher porosity is mainly composed of secondary solution pores caused by the mixture of the early acidic dissolution and late alkaline dissolution. The late alkaline dissolution occurred after the oil and gas entering, so the solution pores are invalid.