Sedimentary System And Multiple-parameter Evulation For Oligocene In Yuquan,Xihu Depression,East China Sea

The oil and gas resources in Xihu Depression accounted for more than 60%of the entire oil and gas resources in the East China Sea shelf basin,whose oil and natural gas reaches 23×10⁸ t and 24×10¹¹m³ respectly.However,the current investment in exploration and development of Xihu Depression is less than 4%,disproportionately severe yield and basin scale,has not formed a large-scale production.There are two main reasons:(1)an unclear understanding of sedimentary system of the main producing gas reservoir section Oligocene—Huagang Formation.(2)a lack of clear understanding of the distribution of high quality reservoir of Huagang Formation.In this paper Oligocene sedimentary environment in Yuquan Area was analyzed in details on the basis of combining rock,electric,seismic data,combined with the conventional deposition research tools to draw diagram deposition parameters.Specific processes included as follows:sequence stratigraphy subdivided-well curve lithology identification standard-single-well sand rate statistics–multi layered seismic attribute fitting sand rate relation and reservoir quality distribution law.The main conclusions are as follows:1?Divide single wells short term cycle in Inpefa Yuquan Area of Xihu Sag Oligocene by using spectral analysis techniques and sum up four kinds of short-term cycles stacking patterns.Combined with seismic reflection termination cycle superimposed single well characterized and the results will divide Oligocene strata into five 3rd sequences,and explain identify every 3rd sequence maximum flooding surface to establish the sequence stratigraphic framework in Yuquan Area of Xihu Depression.2?Detail analysis of tectonic setting,hydrodynamic particle size characteristics,core description and interpretation of sedimentary structures indicated Oligocene in Yuquan Xihu Depression mainly develop sedimentary background delta,river and beach bar.The microfacies of Oligocene in Yuquan,Xihu Depression encomposes clastic river delta,distributary channel,mire,underwater distributary channel,mouth bar and underwater distributary bay microfacies.River and beach bar micro facies is beach side,mud flood,dam,beach,tidal channels and tidal flat sandy microfacies.3?under the overall reservoir quality Oligocene delta front facies distribution based,were scattered like small potatoes.The SQ in the southern inner part develop estuary system of tidal channel,tidal sand bar facies quality reservoir development larger,SQ3 in delta front with the quality reservoir development scale significantly larger than SQ1,SQ2,suggesting that the source SQ3 period was characterized by adequate supply and wide distribution delta.In terms of scale and Continuity,the reservoir quality in SQ5(H3)in the upper half cycle northern Yuquan best work area,is better than that in the lower part.Presumably,during the period of SQ5(H3),the physical properties and ductility longitudinal bar sand body is of high quality.