Seismic Sedimentologic Characterization Of Neogene Delta Reservoir In Southwestern Huizhou Area

Offshore oil and gas exploration and development is an important direction of the national energy strategy.The southwestern Huizhou area is a hot spot of oil and gas exploration and development in the South China Sea.The fine characterization of sedimentary microfacies and sand bodies of ancient Pearl River Delta in Neogene is the key to oil and gas exploration and development in southwestern Huizhou area.In this thesis,seismic sedimentology study on the delta of Zhujiang Formation and Hanjiang Formation in Neogene in southwestern Huizhou area was carried out.The identification and interpretation method of isochronal interface was constructed.Through typical area dissection,the differences of sedimentary microfacies characteristics between near-source area and far-source area in the large marine delta were revealed;methods of favorable sand body characterization were explored.It will guide the exploration and development of Neogene oil and gas reservoirs in southwestern Huizhou area,and provides an example for the study of seismic sedimentology characterization of large deltas.Combining well-side seismic trace analysis with seismic forward modeling,the lithologic association of different sequence boundaries and the corresponding seismic response were summarized.Using the technology of seismic reflection isochronous analysis and slice-based stratigraphic evolution analysis,the key isochronous interfaces were identified and interpreted with seismic data.The sequence stratigraphic framework of eight third-order sequences in the study area and key fourth-order sequences in the typical zone were established,and the technical process of the seismic sedimentological characterization of isochronous interface were formed.Sixteen lithofacies types in study area were summarized;the main microfacies types in the near-source area and far-source area were analyzed;well logging facies and seismic facies templates of delta reservoirs were established.Furthermore,method and workflow of seismic sedimentology characterization which were suitable for the study area were constructed.The method and workflow can be summarized as the following steps: 1)using phase conversion technology for regional lithology analysis;2)Fusing multiple seismic attributes with extreme learning machine to characterize the distribution of sedimentary subfacies of the third-order sequences,and on this basis,the distribution of sedimentary microfacies of the key fourth-order sequences can be characterized;3)In view of the problem that channel sand bodies in the near-source area having multiple periods and large thickness differences,the RGB fusion of frequency-division slices is used to realize the imaging of sedimentary genetic units with different thicknesses;4)In order to solve the problem of channel identification in delta front in near-source area,the nonlinear slicing technology under the guidance of sedimentary model is adopted;5)A pinch-out envelope analysis method based on cascade attribute analysis and multi-data analysis is proposed to solve the problem of thin layer identification of distant sand bar and sheet sand in far-source area.It is concluded as follows.It mainly deposites delta inner front in the near-source area while delta outer front and neritic shelf are mainly in the far-source area.Subaqueous distributary channel and the assemblage of distal bar and sheet sand are respectively the most important microfacies in the near-source area and far-source area.The changes of their development area and the migration of microfacies boundary highlight the evolution of microfacies distribution of the fourth-order sequences.Sequence evolution and sedimentary microfacies jointly control the types and distribution of favorable sandbodies.The sand body assemblages of distal bar and sheet sand(sand body L10low)which develops under the sequence boundary of ZJ4–7 in the far-source area,is close to the sub-order flooding surface and pinches out towards the direction of sea.With good reservoir-cap conditions,it is the typical favorable sand body of thin-layers in the far-source area.The sand body HJ620,which develops in the sequence of HJ6-1 in the near-source area,is an isolated distributary-channel formed sand body in delta front and covered by marine mudstone at the top of the fourth-order sequence.It represents the favorable sand body of the isolated channel type in the near-source area.