川西—川西北地区上三叠统碎屑储集岩成岩作用

DIAGENESIS OF UPPER TRIASSIC RESERVOIR DETRITAL ROCKS IN WEST AND NORTHWEST OF SICHUAN BASIN

王宝清

Wang Baoqing

西安石油大学, 油气资源学院, 西安, 710065

School of Petroleum Resources, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China

川西—川西北地区上三叠统包括须家河组和香溪群;主要沉积相类型有河流三角洲、海湾、湖泊和冲积扇.上三叠统储集岩主要由长石岩屑砂岩、岩屑长石砂岩、岩屑砂岩、长石石英砂岩、岩屑石英砂岩及少量长石砂岩组成.岩石碎屑颗粒含量81%~95%,碎屑中有较多长石和岩屑,具低的成分成熟度和高的结构成熟度.原始孔隙度的45.0%~77.5%是由于压实作用而丧失的.胶结作用对储层的破坏性仅次于压实作用,包括自生石英、长石、粘土矿物和碳酸盐矿物的沉淀.石英加大的深度可能大于1 800~4 080 m.受有机质影响,碳酸盐胶结物具较低的δ13C值(PDB),为-4.85‰~2.91‰;由于淡水淋滤和深埋藏,有较低的δ18O值(PDB),为-16.97‰~-7.86‰.溶蚀作用是对储集岩最重要的建设性作用,以长石溶蚀最为常见.粘土矿物以伊利石为主,无蒙皂石.镜质体反射率为0.81%~2.48%,推测古地温大部分在85~160℃.储集岩成岩作用已进入到晚成岩作用阶段的中期.裂缝在很大程度上改善了储集性能.由于压实作用和胶结作用影响大,溶蚀作用影响小,储集岩以低孔、低渗为特征.

The upper Triassic includes the Xujiahe Formation and the Xiangxi Group in the west and north-west of Sichuan Basin.The main types of sedimentary facies are fluvial-dominated deltas,embayment,lake and alluvial fans.The upper Triassic reservoir rocks consist of feldspathic litharenite,lithic arkose,litharenite,subarkose and sublitharenite.Clastic grains,which contain abundant feldspar and rock fragments,make up 81% to 95% of rocks by volume.Sandstones are characterized by low composition maturity and high texture maturity.Primary porosity lost 45.0% to 77.5% due to compaction effect.Cementation,including precipitation of authigenic quartz,feldspar,clay minerals and carbonate minerals,is the second process contributing to porosity reduction.Influenced by organic materials,the δ13C values for carbonate cements,which range from-4.85‰ to 2.91‰(PDB),are low.Because of leaching with meteoric water and deep burial depth,the δ18O values for carbonate cements,which range from-16.97‰ to-7.86‰(PDB),are also low.Dissolution effect,which is mainly the leaching of feldspar,is the most important process for reservoir quality improvement.Clay minerals are mainly illite,and smectite is absent.Vitrinite reflectance ranges from 0.81% to 2.48%,indicating 85-160 ℃ for most ancient geotemperatures.Diagenesis proceeds to middle-late stage.Fractures have improved reservoir characteristics to a great extent.Because the influence of compaction and cementation is strong,and the influence of dissolution is weak,reservoir rocks are characterized with low porosity and permeability.

https://doi.org/10.11781/sysydz200801069