Abstract:

Faults are the main oil-gas migration pathways in Chepaizi area and can also form associated hydrocarbon re-servoirs,thus research on fault sealing ability is of great significance for confirming spatial distribution of reservoirs in the study area.Through qualitative analysis of fault characteristics and the timing between faulting and hydrocarbon generation and expulsion,and quantitative evaluation of factors controlling sealing ability such as juxtaposition of lithology,shale smear,and normal stress on fault surface,we studied the sealing ability of two major faults(F1 and F2)in northeastern Chepaizi Uplift,and performed comprehensive judgment by using fuzzy evaluation method.The results show that the sea-ling abilities of F1 and F2 feature in ‘vertical periods and lateral segmentation’.Vertically,the fault sealing ability can be divided into periods,including Cretaceous(K),the first member of Neogene Shawan Fm (N₁s¹),2^nd member of Neogene Shawan Fm(N₁s²),and 3^rd member of Neogene Shawan Fm(N₁s³).The sealing ability of faults in Cretaceous is good as a whole except for the southern segment of F2.For N₁s¹,sealing ability of F1 is good in the northern segment,poor in the middle segment,and good to poor in the southern segment,while that of F2 is poor to fair as a whole.For N₁s²,fault sealing abilities are good as a whole.For N₁s³,fault sealing abilities are poor as a whole,except for the middle segment of F2 whose sealing ability is good.

Key words: shale smear, normal stress on fault surface, fuzzy evaluation, fault activity stage, fault sealing ability, Chepaizi Uplift, western margin of Junggar Basin