| By the “moldic” and “residual thickness”methods and the seismic phase tracing and contrasting, the karst paleogeomorphology is analyzed to the Qianmiqiao Buried Hill in Huanghua Depression, Bohaiwan Basin. It is revealed that karst geomorphic of Qianmiqiao buried hill had successively experienced three evolution stages including the exposure and development during Caledonian-Hercynian period, the exposure and reformation during Indosinian-Yanshan period and the sinking, burial and formation during Himalayan period. The development and distribution of palaeokarst caves are not only under control of the geomorphic form and ground water surface, but also are closely related with the lithologic combination, palaeohydrologic environment and fractures. Accompanied with the continuous uplifting of the crust and the unceasingly descending down of regional water table during Caledonian-Hercynian period, palaeokarst caves evolved into multicycle bedded distribution with arenaceous fulling in pores and little available pores preserved. Influenced by fracture system, the palaeokarst caves were distributed with certain randomness and most of pores were partly filled with chemical matters during the Indosinian-Yanshan period. These caves and pores
are the present significant reserving spaces for oil and gas in the buried hill. By using drilling and well logging information and cave fillers, the existence and the distribution of the palaeokarst caves may be distinguished, which can provide some information for the comprehensive reservoir evaluation to buried hill reservoirs in oil and gas fields. |
