南苏门答腊盆地J区中新统进积三角洲成因砂体叠置样式

南苏门答腊盆地J区中新统进积三角洲成因砂体叠置样式及空间演化规律认识不清,制约了该区非构造油气藏的精细勘探.基于高精度成因地层分析,结合区域地质背景、岩石相类型、测井响应及地震特征,识别进积三角洲成因单元类型,根据其空间展布规律建立反映进积三角洲砂体结构的沉积模式,并提出三角洲砂体成因-结构分类方法和砂体叠置样式约束下的储层预测方法.研究区可识别出水下分流河道、河口坝、席状砂、分流河道间和前三角洲泥等5种成因单元.进积三角洲沉积初期发育单成因孤立砂体,可形成上倾尖灭岩性圈闭、多层薄砂反向断块-岩性圈闭;沉积中期以双成因叠加复合砂体为主、单成因孤立砂体为辅,可形成多层反向断块-岩性圈闭;沉积后期以多成因切叠复合砂体为主、双成因叠加复合砂体为辅,可形成多层复杂断块-岩性圈闭、块状地层不整合圈闭;从下到上呈单成因孤立-双成因叠加-多成因切叠砂体叠置样式.

Superimposition patterns of sandbodies in Miocene progradational deltas in Block J,South Sumatra Basin

The detail exploration of non-structure hydrocarbon reservoirs in Miocene progradational delta in Block J of South Sumatra Basin is restricted by the unclear understanding of the superimposition patterns and spatial evolution law of sandbodies.Based on the analysis of the high-resolution sequence stratigraphy,regional geological setting,lithofacies,log⁃ging response,and seismic features,the genetic unit types of progradational delta are identified.A depositional model re⁃flecting the sandstone architectures of progradational delta is established according to their spatial distribution.The genet⁃ic-architecture sandbody classification and reservoir prediction methods restricted by the sandbody superimposition pat⁃terns are further proposed.The results show that five genetic unit types are identified in study area,including underwater distributary channel,mouth bar,sheet sand,distributary inter-channel and pre-delta mud in the deltaic depositional sys⁃tem.At early stage of progradational delta sedimentation,the isolated mono-genetic sandbodies were developed and the up⁃dip tip-out lithologic trap and multi-layered thin sand reverse block-lithologic trap formed.At the middle stage,the super⁃imposed bi-genetic sandbodies were mainly developed and followed by isolated mono-genetic sandbody,and multi-layered reverse block-lithologic trap formed.At the final stage,the multi-genetic incised superimposed sandbodies were mainly de⁃veloped and followed by bi-genetic sandbodies,and multilayer complex fault block-lithologic trap and block formation un⁃conformity trap formed.From bottom to top,the superimposed pattern shows as the isolated mono-genetic sandbody-super⁃imposed bi-genetic sandbodies-multi-genetic incised superimposed sandbodies.