Abstract:

Tight sandstone has been an important field of exploration and development of oil and gas in China recently. The tight sandstones of Chang 7 Formation of Longdong area in Ordos Basin mainly developed into braid deltas and gravity flow sedimental sand bodies. And the latter has great potential in exploration and development. On the basis of research of regional structure, paleoclimate, ancient landform and sedimentary systems, we applied the technology of sedimentary simulation to recreating the formation processes and main controlling factors of the researched area, the Chang 7 Formation. Under laboratory conditions, sedimentary facies of semideep to deep lakes are mostly sandy debris flow, turbidite and deep lake mud. The experimental research indicates that the main controlling factors to impact the formation and evolution of gravity flow sedimental sand bodies are: (1)sediment concentration (decides the sediment type of gravity flow); (2)the shape of the bottom of a lake basin (controls the distribution of sand body of gravity flow); (3)the lake stage and flow rate (decide the sedimentary thickness and the scale of gravity flow); (4)the intersection of various sources (decides the transverse connection of gravity flow). Also, by analyzing and comparing the results of the experiment, we predicted the areas with favorable reservoir distribution. We combined the original geological model of Longdong area with the results of the simulated experiment and established the sedimentary pattern of Chang 7 Formation of the Triassic in Longdong area under the condition of sedimentary simulation experiment.

Key words: tight sandstone, sedimentary simulation, sandy debris flow, turbidite, Longdong area, Yanchang Formation, Ordos Basin