The Study On Seismic Sedimentology Of Guantao Formation In The Dawangzhuang Area Of Raoyang Sag

The Guantao Formation in the Dawangzhuang area of Raoyang Depression is of river facies,with rapid variation of sand bodies both laterally and vertically.In addition to this,well nets distributes unequally,which results in the insufficient understanding of the facies and the distribution of sand bodies in the study area,especially in places where wells are sparse.This paper takes the seismic sedimentology theory as the core guiding ideology.First,a sequence stratigraphy method was used to establish a unified isochronal stratigraphic framework of well data and seismic data in the entire region.The Guantao Formation was divided into 3 level-four sequences and 7 level-five sequences,and then make full use of the interpretation advantages in the horizontal resolution of three-dimensional seismic data,and by applying 90°phase rotation,frequency interpretation,stratal slice,and other key techniques of seismic sedimentology within the established sequence stratigraphic framework constraints,the sand bodies in the targeted interval was detected in the seismic petrology and seismic geomorphology method,which was at the same time supplemented by seismic waveform classification to guide sedimentary microfacies identification and waveform indication inversion to improve accuracy of sand body prediction,which provided conditions for the prediction of favorable targets in the study area.According to the facies analysis of single-well and well-lines,it is considered that the target strata in the study area are mainly composed of braided river facies and meandering river facies,of which the braided river contains four types of microfacies:center bars,river channels,inter-channel depressions and inter-channel beach,and meandering river can identify microfacies like channels,natural levee,floodland.On the basis of filtered seismic data,the initial 3D seismic data volume is subjected to 90°phase shifting,aligning the lithologic interface with the peak-to-valley interface of the sismic wave,thus was given the seismic axis ithologic significance,and a three-dimensional lithology body is obtained;On the basis of the phase-transformed seismic data volume,stratigraphic slices were extracted to observe the distribution and vertical evolution characteristics of the fluvial sand bodies in the Guantao Formation.It was found that the Guantao Formation was the consequence of datum level moving from a low to high.Seismic attributes were extracted para-sequences of the Guantao Formation and attributes were optimized.Three relatively independent properties of the root mean square amplitude,instantaneous amplitude,and instantaneous phase were selected,and sandstones distribution was predicted in areas lacking enough wells.Seismic facies waveform classification was used to guide sedimentary facies division for selected attributes;wave impedance curves were extracted from coring wells,and all seismic data were inverted using the waveform indication method to improve reservoir prediction accuracy.Based on the above analysis,a systematic analysis of the distribution characteristics of the microfacies of the Guantao Formation was carried out.The study concluded that the overall facies of the 3rd member of Guantao Formation was a braided river,with the lowest datum level during the first para-sequence deposition and a large river cover area.In the second para-sequence depositional period,the source of material supply decreased and the river channel narrowed;during the deposition period of the third para-sequence,the scale of the river had increased.The second section of the Guantao Formation is dominated by meandering river,of which the fourth para-sequence is a high-curvature meandering river,and the Vth parasequence period is a low-curvature meandering river.In the early deposition period and late depositional period,the depositional types were different.The depositional period of the No.VI parasequence was a low-curvature meandering river.By the depositional period of the No.VII parasequence,the datum level declined,and it evolved into a braided river sedimentation..Combining local structural features,characteristics of cap rock,reservoir rock and their combination,and sedimentary facies characteristics,nine beneficial targets in Ng₁¹ and Ng₃³were optimized.