鄂尔多斯盆地北部上古生界储层成岩作用

DIAGENESES OF UPPER PALEOZOIC RESERVOIRS IN NORTH E′ERDUOSI BASIN

根据X衍射、包裹体、胶结物氧、碳同位素分析及显微观察 ,影响鄂尔多斯盆地北部上古生界碎屑储集岩孔隙发育和演化的主要成岩作用有压实作用、碎屑矿物蚀变作用、胶结作用、交代作用、溶蚀作用和自生粘土矿物生长作用。成岩序列为机械压实作用→碎屑矿物蚀变→自生绿泥石粘土边→石英胶结作用→溶蚀作用→自生粘土矿物→碳酸盐胶结。不同地区经历的成岩作用不同 ,造就了孔隙度演化的差异 ,形成南差北好的储层物性 ,即 :北部地区砂岩估算的初始孔隙度为 37% ,至晚成岩B期孔隙演化至 10 .33% ;中部地区砂岩初始孔隙度为38% ,至晚成岩B期为 6 .98% ;南部地区砂岩初始孔隙度为 39% ,至晚成岩B期仅为 6 .1%。

According to the data on X-ray diffraction, inclusion, isotope analysis of the oxygen and carbon in cementing matter, and microscope observation, it was determined that the major diageneses affecting the development and evolution of the pores in the clastic reservoir rocks of Upper Paleozoic in North E′erduosi Basin are compaction, the alteration of clastic minerals, cementation, metasomasis, corrosion and the growth of authigenic clay minerals, the diagenetic sequence being as follows: mechanic compaction→the alteration of clastic minerals→authigenic chlorite clay rim→quartzitic cementation→corrosion→authigenic clay minerals→carbonate cementation. The diageneses suffered at difference regions were various, which causes the difference in porosity evolution. The reservoir petrophysical property in the north is better than that in the south. In other words, the estimated initial porosity of sandstones in the north part was 37 percent and decreased to 10.33 percent in stage B of late diagenesis; that in the central part was 38 percent and decreased to 6.98 percent; and that in the south part was 39 percent and decreased to 6.1 percent only.