| The Triassic Yanchang Formation in the Longdong area of the Ordos Basin is currently one of the important oil-producing layers.The deep lake slope gravity flow sedimentary area contains abundant oil and gas resources.Finding a favorable target area is the primary goal of today’s research.Therefore,to explore the sequence stratigraphy,geomorphology and sedimentary filling evolution characteristics related to the reservoir in the slope area of the lake basin will further clarify the distribution characteristics of its favorable sand bodies,which has important research significance.Based on the 3D seismic data of Qingcheng area,supplemented by drilling and logging data,combined with previous research results,this paper studies the progradation phenomenon on the seismic section of the deep lake slope area in the middle and upper part of the Yanchang Formation,such as progradation body identification,sequence division,paleogeomorphic restoration,sedimentary facies analysis,and filling evolution analysis.The main conclusions are as follows:(1)Based on the well-seismic isochronous correlation of strata,a total of P1-P5five-stage progradation bodies were identified in the middle and upper part of the Yanchang Formation in the study area.Using wavelet transform and INPEFA curve analysis,5 long-term cycles are divided,which correspond to the pre-volume P1—P5from bottom to top.The progradation bodies P1—P4 deposited in the form of lens to the center of the lake basin,and P5 deposited in the form of accretion.A new sequence stratigraphic framework was established,which is inconsistent with the traditional lithologic stratigraphic stratification and shows the characteristics of "through layer".(2)The bottom of Yan 9 Member is selected as the datum plane for layer leveling,and the paleogeomorphology in the middle and upper part of the Yanchang Formation is restored by using three-dimensional seismic data.The paleogeomorphology as a whole shows obvious step-like morphological characteristics.With the slope break zone as the boundary,the gentle slope zone,slope zone,depression zone and other geomorphic units are identified.The P1-P4 paleotopography has strong inheritance,and its slope zone continues to advance to the deep lake area,and the paleo-dip angle gradually becomes smaller.According to the results of geomorphological restoration,combined with the depth of the water body,the evolution characteristics of the lake basin in the middle and upper part of the Yanchang Formation are characterized and characterized.It shows that the front edge of the delta from P1 to P5 continues to advance,and the lake sedimentary range gradually becomes smaller until it disappears.(3)Through core observation,seismic and logging facies marks,combined with previous research results,the sedimentary facies of the P1—P5 sedimentary period in the study area are divided into braided river delta,deep water gravity flow and lake 3facies,6 subfacies and 9 microfacies.Through seismic attribute extraction,the seismic well-connected facies and seismic plane facies are analyzed.The results show that the gentle slope zone of the P1-P5 progradation body is distributed in high amplitude and strip shape.The upper part of the slope zone is rich in mud,and "high amplitude" areas are developed locally;The lower part of the slope zone to the depression zone has a medium-low amplitude,which is divergent and striped.Based on the study of seismic geomorphology and sedimentary microfacies,the distribution characteristics of gravity flow sediments are clarified,and the sand body distribution model of "upper gentle slope zone(rich delta front sand)-central slope zone(rich mud)-lower depression zone(rich gravity flow sand)" is established.P1-P5 shows that the multi-phase superposition gradually advances to the lake basin,showing the characteristics of oscillating lake retreat and filling sedimentation.(4)The sedimentary filling evolution process under the sequence framework of the P1-P5 sedimentary period in the study area is determined,which corresponds to the last three stages of the strong depression stage,the uplift stage and the shrinking and disappearing stage of the typical depression lake in the craton.Among them,the P1 sedimentary period is the strong depression stage of the Ordos Lake Basin.After the rapid and large-scale lake invasion,the scope of the lake basin expanded significantly.The lake basin entered its heyday,the basin was in an under-compensated state,and a set of oil-generating rocks was formed.During the P2 sedimentary period,the structure tended to be stable,the basin was in the filling and filling period,the lake began to fill with sediments,the supply of material sources in the southwest was sufficient,and the delta front sand body accumulated to the center of the lake basin.The P3 sedimentary period inherited the geomorphic pattern of the previous period.After a small-scale lake invasion,the lake shoreline gradually retreated,and highly constructive delta deposits developed into the basin.The P4 sedimentary period is the stage when the lake basin shrinks and disappears.The lake basin shrinks rapidly,and the delta deposits in the southwest provenance area accumulate substantially to the northeast of the basin.During the P5 sedimentary period,the lake basin continued to rise until it died out... |
PDF Full Text Request