Fine characterization of braided river reservoir architecture with sparse well pattern based on intelligent fusion of multiple seismic attributes-- A Case study of Guantao Formation of C-6 Oilfield , Bohai Bay Basin

Key words: 
• braided river /
• reservoir architecture /
• DFNN neural network /
• Guantao Formation /
• Bohai Bay Basin

Abstract: C-6 Oilfield is one of the most principal oilfields of Caofeidian oil province with hundred million cubic metre of reserves. The third oil group of Guantao Formation (N1gⅢ), the main production zone of C-6 Oilfield, is sand-rich braided river deposit. The architecture and connectivity of braided river sandstone are the key geological factors affecting the development effect of the Oilfield. Calibrated with limited log data, intelligent fusion technology of multiple seismic attributes was introduced to finely characterizes the spatial distribution of the level-4 architecture units of the braided river reservoir. According to log interpretation, N1gⅢ of C-6 oilfield mainly develops two types of level-4 architecture units, namely, channel bar and braided channel, and braided bar is the best reservoir with high sandstone thickness and excellent physical properties. Based on seismic attribute extraction and correlation analysis with lithological and physical parameters, reflection intensity, relative impedance, sweet point, original amplitude, envelop were chosen as intelligent fusion seismic attributes with Deep Feed-Forward Neural Network (DFNN) algorithm under the supervision of porosity. The 3D attribute of DFNN fusion, representative of lithology and petrophysical property, largely improves the detecting ability of braided river sandstone unit and its boundary, and can be used to finely characterize the plan and section distribution of braided river level-4 architecture units effectively. A NE-SW braided flow zone was developed in N1gⅢ of C-6 oilfield, which could be internally sub-divided into 15 rhombic level-4 architecture units of the braided bar. Distributary channels, another level-4 architecture units, surrounded braided bar in a narrow strip. The level-4 architecture interface between the two units played as seepage barriers for fluid migration. The braided bars cut and overlapped one another vertically, forming “big bar and small channel” plan reservoir architecture pattern. The fine characterization results deepened the understanding of the reservoir connectivity of the braided river reservoir with sparse well pattern, which provided direct geological bases for the making of optimized adjustment plan of C-6 Oilfield.