Chang 8 channel sand identification with 3D seismic lens reflections in Daijiaping survey, Southwestern Ordos Basin
Pan Jie1, Liu Zhongqun2, Pu Renhai1, Zhou Sibin2, Fan Jiuxiao2, Bai Sheng1
1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an, Shaanxi 710069, China;
2. Research Institute of Exploration and Exploitation, Huabei Oilfield Branch Co., SINOPEC, Zhengzhou, Henan 45006, China
Abstract：Due to the poor quality of Loess 3D seismic data and few contrast of wave impedance between sands and mud,it is very difficult to identify channel sandstone reservoirs of Chang 8 Mem,Yanchang Formation on both normal sections and broaden-frequency sections in the Ordos Basin.Chang 8 channel sandstones of Yanchang Formation can produce lens reflections both on both normal and broaden-frequency sections when they are thick enough.On seismic sections lens of Chang 8 is shown as falling down event of Chang 813 bottom,or Chang 812 as widen trough event or one additional crest event.According to amplitude and waveform characteristics of Chang 8 on broaden-frequency sections,lens reflection can be divided into seven categories.The first four types are most common,and they are square trough with a peak,square trough,round trough,and round trough with a peak.Sand contains probability in the four types of lenses gets less from the first one to the last one.Multiples caused by coals of Yan'an formation in this area may generate false lens response.This will mainly affect delineating Chang 8 channel sandstone.Drilling does not encounter sandstone this may be due to mud filled plug in abandoned river,or inaccurate lens center delineation on seismic sections.A part of Chang 8 thicker sandstone does not form the lens reflection; this may be because impedance contrast between sand and mud is too small.
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