Study On Sequence And Sedimentary And Lithologic Traps For Zhujiang Formation 21-18.5Ma In Huizhou Depression,Pearl River Mouth Basin

The Huizhou depression located in the east of the Pear River Mouth Basin,which is rich in hydrocarbons.At present,accompanying with development of exploration,structural traps of Huizhou depression were decreased and exploration difficulties were increased,so the seeking of lithological trap became an inevitable trend.Studies on stratigraphic and lithologic traps have positive and practical significance for further exploration in the Pearl River Mouth Basin.In this paper,on the basis of analyzing sequence features and depositional systems distribution characteristics of Zhujiang Formation 21Ma-18.5Ma in the southwest region of Huizhou Depression,combined with sedimentary facies,structural characteristics,migration accumulation,and other factors to determine the favorable zone of lithologic traps by overlapping idea.Finally proposed well site deployment and comprehensive technical evaluation.Based on the integrated analyasis of cores,welllogging.Seismic data and other basic data,Zhujiang 21Ma-18.5Ma Formation can be identified a sub flood surface and three local flood surface,then divided ulterolrly into five 4th order sequences,in correspondence with each set of sand group.The sequence stratigraphic framework was established.Through the establishment of a high-resolution sequence stratigraphic evolution model,the thesis clarifies a clear division of the updip pinchout belt periods in the delta front sandbodies,and recognizes that deposition transform surface of the fourth grade sequence controls the distribution of oil and gas.According to the research on the sedimentary facies within the framework of sequence stratigraphy,the main types of sedimentary facies in this area are fuvial dominated delta and tidal delta,accompanied by tidal flats,shallow shelf facies and carbonate platform facies.The delta front is a favorable zone for the formation of lithologic trap.After identifying the types of sedimentary facies,in the conditions of the less well,taking full advantage of the seismic data,finally map out the the sedimentary facies distribution sedimentary facies in unit of 4th order sequence.In doing so,the updip pinch out sandbodies in the delta front can be predicted.Based on the analysis of the structural characteristics of the study area,the study found that the west dipping nosing structure by the side of the structure trap is the best tectonic background to form updip pinchout lithologic trap.The concept of ridge will be introduced to perform analysis to the structure map of different sand ridge groups of L series on the quantity,structure amplitude and ability to gather oil and gas.In the aspect of accumulation,the concept of dispersion,convergent beam and separation trough valley are introduced to divide the lithologic trap system,and at the same time,an integrated accumulation system including depression,slope,ridge and ring is proposed,defining 7 accumulation systems into four types.Three target zones are chosen according to structure,accumulation and sedimentary pinchout lines and special importance is attached to the division and evaluation of the HZ22-8-HZ25-14 zone.