四川盆地德阳—安岳凹槽中段及东侧槽缘带震旦系灯影组沉积格局变化及其油气勘探意义OA

The Deyang-Anyue trough in the Sichuan Basin plays a vital role in controlling the formation and distribution of gas reservoirs in the Sinian Dengying Formation.However,the contentious stratigraphic division and limited studies on sedimentary characteristics and evolution process in this area impede the exploration progress of the Dengying Formation gas reservoirs.To clarify the stratigraphic characteristics and sedimentary pattern variations,the Dengying Formation in the study area was redefined using new well logging data(cuttings,cores,and conventional logs)and 3D seismic data to determine its distribution,and the sedimentary characteristics and evolution process were thoroughly discussed.The following results are obtained.(i)The Dengying Formation within the trough is generally complete in stratigraphic sequence,with only the absence of the third and fourth members of the Formation(Deng 3 and Deng 4 Members for short)in the southern part.The trough had already formed by the end of the sedimentary stage of Deng 2 Member.Moderate filling during the Deng 3 Member stage lead to a slight reduction in the difference between terrain elevations inside and outside the trough.The paleotopography in the Deng 4 Member,largely inherited from the late stage of Deng 2 Member,accentuates the geomorphological contrast inside and outside the trough.(ii)The sedimentary facies such as slope-shelf,platform margin,semi-restricted platform,and mixed platform are identified in the Dengying Formation within the trough and its periphery,with their types and distribution controlled by the trough morphology and scale.(iii)The sedimentary evolution progresses in stages.In the early stage of Dengying Formation,differential subsidence and dissolution thinned original facies zones in the Deng 1 and Deng 2 Members,recording the initiation of the trough.In the middle stage,the geomorphological contrast triggered sedimentary differentiation,resulting in the distribution of low-energy slope-shelf deposition within the trough and high-energy platform deposition outside the trough.In the late stage,tectonic uplift caused stratigraphic exposure and erosion,making the Deng 3 and Deng 4 Members absent locally.(iv)The analysis of stratigraphic division and reservoir-development characteristics shows that the areas favorable for mound-shoal complex development are identified,including the PT1-PT103-PS3,MX8,and GS137 wellblocks in the Deng 1 and Deng 2 Members and the DT1,PT103-PT101-GS102 wellblocks in the Deng 4 Member.This study clarifies the stratigraphic characteristics,sedimentary features,and evolution of Dengying Formation in the middle section and eastern margin of the Deyang-Anyue trough,providing a significant geological basis for efficient gas exploration.