Research On Oil And Gas Accumulation Conditions Based On Seismic Interpretation In The Second Member Of Shahejie Formation In The Southern Part Of Dawangbei Sag, Chezhen

The 2nd member of Shahejie Formation in Dawangbei Depression in Chezhen Depression is the main oil-bearing strata in this area and it has good exploration potential.Beach-bar reservoir is an important target for reserves improvement in Dawangzhuang Oilfield.The research area has not achieved breakthroughs in exploration in addition to the D101 block due to the reason:? The size of beach-bar sand bodies is small;? the development of fractures in the area;?it is difficult to identify the traps;?the conditions for reservoir formation have great differences.In recent years,with the continuous improvement of exploration and development,3D seismic has been extensively applied to the study of the reservoir in this area,providing the basis for an in-deep understanding of the reservoir-forming conditions of beach-bar reservoirs.Under the guidance of petroleum geology and the applications of modern geophysical methods,this study re-analyzed the reservoir-forming conditions of the 2nd member of Shahejie formation,studying the main controlling factors of reservoir formation of the beach-bar reservoir in-deep,establishing the reservoir-forming model and finally predicted the favorable blocks in order to provide an effective reference for the next exploration and development.The main results achieved and understandings are as follows:1.On the basis of fine structural interpretation of the 2nd member of Shahejie formation.The characteristics of fracture development and its distribution were identified.In the area,normal faults are developed near the east-west and southwest-northeast,and secondary faults are well developed.According to the basic trap theory,19 structural traps were identified on the top structural map of the 2nd member of the Shahejie Formation.A large number of fault block traps and fault-nose traps were developed in the study area,and the fault-nose traps were widely distributed and had a large size.2.Combing seismic time-frequency analysis techniques,logging and geological logging data,dividing target formation into one third-order sequence and fourth-order sequence under the guidance of high-resolution sequence stratigraphy.The development of sand bodies in 2nd member of Shahejie formation is controlled by the sedimentary base-level cycle,both of the dam sandbodies and beach sandbodies are mostly developed in the mid-lower part of the ascending semi-circle and the upper-mid part of the falling semi-circle.3.The sedimentary characteristics and paleo-geomorphologic environment in the 2nd member of the Shahejie Formation were clarified.The analysis showed that the dam sandboies are more likely to form oil reservoirs than beach sandbodies,and the overlapping dam sandboies are favorable reservoirs for oil and gas accumulation.This study identified 12 different interpretation models and 6 vertical lithofacies combinations under 2 hydrodynamic conditions Combined logging phase and seismic facies analysis.It shows that the overlapping dams has high continuous and strong amplitude of seismic features,and beach-bar overlapping bodies has medium continuous and medium to strong amplitude of seismic features.4.Based on the analysis of paleo-geomorpholoy backgroud and sedimentary analysis,the development zones of overlapping dam sandbodies were characterized using Spectral decomposition technique and seismic attribute slices to indicate favorable development area for lithologic traps.In combination with the results of seismic inversion,11 development zones of lithologic traps were identified.These areas mainly developed sandstone up-dip traps and sandstone lens traps.5.The 2nd member of Shahejie Formation has good conditions for hydrocarbon accumulation.The specifics are as follows:The 3nd member of Shahejie formation,which is the underlying source rock is in the mature-oil generation stage,with large thickness and good continuity,and has great potential for hydrocarbon generation.The traps formed early with numerous types and widely distributed,and the structural-lithologic compound traps are advantageous area for oil and gas accumulation.Through typical reservoir anatomy,the fault is considered to be the most important controlling factor for the distribution of reservoirs.The degree of reserviors development controls the size of the reservoirs.Based on this,favorable blocks were identified.