MACROSCOPIC CHARACTERISTIC OF BRAIDED DISTRIBUTARY CHANNEL SANDBODY RESERVOIRS AT BAOBEI BLOCK, THE BAOLANG OIL FIELD IN THE YANQI BASIN

The reservoirs at Baobei block, the Baolang oil field in the Yanqi Basin are composed of braided distributary channel sandbodies in lower delta plain.Based on observation of drilling cores,the authors divided elaborately the thick braided distributary channel sandbodies into several single channel sandbodies by virtue of well logs.The core beach sediments are the most favorable reservoirs in a distributary channel sandbody.According to development of core beach sediments,three sorts of distributary channel sandbodies were recognized,which occur in asymmetrical lens shape,wide and thin dish shape,and wide and thick trough shape in cross section respectively.Additionally,the authors recognized three kinds of sandbody unit reservoirs with difference macroscopic anisotropy.These three kinds of reservoirs consist of isolated distributary channel sandbody,lateral stacked distributary channel sandbody,and vertical stacked distributary channel sandbody,which occur as long stripes,wide zones,planes in plane figure,and show local connection,low connection and high connection respectively.The development of single channel sandbody and sandbody units was controlled by lake level's fluctuation,basement's subsidence and energy of flows in channel.High energy flow and rapid steady subsidence of basement resulted in wide and thick single sandbody and sandbody unit,and lake level's rising caused the formation of successive partings and low connecting sandbody unit.Furthermore,the authors give the formation model for single sandbody and sandbody's combination.