| The Middle Triassic Leikoupo carbonate rock is divided in five members (from T2l1 to T2l5) in Yilong-Pingchang Area, Northern Sichuan Basin. The Leikoupo 5th Member has been denudated up and at the top of Leikoupo 4th Member (T2l4) is directly unconformably overlied by Xujiahe Formation (T3x) . The residual thickness of leikoupo Fm. is from 800m to 950m. Extensive dissolution had been undergone in a range of over then to a hundred meters at the top of T2l4 Member, which resulted in epidiagentic karstification and formed karst breccia, silicification and dissolved ditches, holes, caves and fractures. Contributed to the karstification, a large amounts of dissolution space was produced, in which parts of dissolution space were filled all or locally with argillaceous material that had fallen from the overlying T3x. Acording to the analysis of imaging logging and well cores, it is shown that three karst zones develop, including vertical seepage flow, horizontal underflow and deep slow flowage zones. Overall, the development of the reservoir with the vertical seepage flow zone is better than that with the horizontal underflow zone and the development of the reservoir with slow flowage zone is poor. Besides, the karstification is more extensive and reservoir property is better in higher location. Based on the map of the drawing energy storage coefficient(ESC) distribution of T2l4, it is suggested that the areas of Well A21-Well A19, Well A22-Well A23 and Well A160, in which the ESC are all great than 0.6, are the potential reservoir areas. |
