Abstract:

Applying the principles and methods of high-resolution sequence stratigraphy, and combining with the data of exploration wells and development wells in encrypted network of wells, the authors identified 41 short-term base-level cycles of 7 types, which were formed under the conditions of deeping upward, shallowing upward, symmetrical in different accommodation space in Fuyu oil layer of Chao 1-Chao gas 3 blocks, and makes detailed analysis on the genesis and characteristics based on the sedimentary dynamics. According to the structural feature and stacking pattern of short-term base-level cycle, the authors established seven medium-term base-level cycles and identified two long-term base-level hemicycles by accompanying local indicator layers, and thus established the high-resolution sequence stratigraphic framework. In the study area, sand body is generally absent in the long-term base-level fall hemicycles, but in the early long-term base-level rise hemicycles, the thickness and effective thickness of sand of river-facies are  significant, ratios of sand to mud are high, oiliness is good, and with the long-term base-level rising, the sedimentary environment turned to the delta system, the shore lake and the shallow lake, sand and oiliness gradually decrease. Moreover, each medium-term base-level, sand and its oilness in the transform zone from subsidence to elevation developed relatively best in the whole medium-term base-level cycle.

Key words: high-resolution sequence stratigraphy, base-level cycle, Fuyu oil layer, sedimentary environment, sand body, oiliness