旬邑地区三叠系延长组长8_1储层成岩作用与孔隙演化

Diagenesis and Porosity Evolution in the Chang 8_1 Reservoirs of the Triassic Yanchang Formation in the Xunyi Area,Ordos Basin

通过铸体薄片、扫描电镜、高压压汞、X射线衍射等方法对旬邑地区延长组长81储层成岩作用进行研究,在此基础上分析储层孔隙演化过程,讨论成岩作用差异对储层孔隙演化的影响。结果表明:长81砂岩储层由岩屑长石砂岩和长石岩屑砂岩组成,主要受压实作用、胶结作用及溶蚀作用的影响。长81储层原始未胶结砂岩孔隙度为36.01%,压实作用造成孔隙度损失为20.37%,早期胶结引起孔隙度降低8.51%,溶蚀作用使孔隙度增加3.25%,晚期胶结导致孔隙度下降5.54%。砂岩岩性差别对储层孔隙演化影响较小,成岩作用的差异是影响储层孔隙演化的主要因素,直接制约孔隙演化过程和储层质量。

The diagenesis in Chang 8 1 reservoirs of the Triassic Yanchang Formation in the Xuuyi area of Ordos Basin is studied by means of thin sec- tion, casting film, mercury injection and X -ray diffraction（ XRD. Porosity evolution of Chang 8 1 reservoirs is analyzed, and the influence of differential diagenesis on porosity evolution is discussed. The primary rock types of the reservoirs are lithic arkose sandstone and feldspar lithic sandstone. Quality of the reservoirs is mainly affected by compaction, cementation and dissolution. The porosity of the unconsolidated sands is 36.01% , the porosity of the res- ervoirs is decreased by 20.37% as a result of compaction, thus the porosity of the reservoirs decreased by 8.51% due to early cementation. Afterwards, the improvement of the reservoir pore as a result of dissolution is obvious, contributing the increase of porosity by about 3.25%. The loss of porosity is 5. 54% by late cementation. The difference of rock types has little influence on the porosity evolution of the reservoirs, so the difference of diagenesis is the main factor that affects porosity evolution of the reservoirs, which directly controls the porosity evolution process and the quality of the reservoirs.