| The northwestern margin of Junggar Basin is an important oil and gas producing area in China,among them Fengcheng area is located in the Wuxia fault zone.With the further exploration of Fengcheng area in recent years,many oil reservoirs have been found there.Predecessors have many controversies on the sedimentary characteristics and evolution of Fengcheng area.In this paper,the sedimentary evolution characteristics of Jurassic strata in Fengcheng area are described by establishing sequence stratigraphic framework.Through the investigation of the predecessors' work,the analysis of geological data such as core,logging and earthquake,the sedimentary facies types of Jurassic strata including Including the Badaowan Formation,Sangong River Group,Xishan Kiln Group,Toutun River Group and Qigu Group in Fengcheng area,in the northwestern Junggar Basin,were intensively studied.Five sequence boundaries of the three order are identified in the target horizon including Badaowan group,Sangonghe group,Xishanyao group,Toutunhe group and Qigu group which is divided into 4 third-order sequences,and 11 system domains.Sequence I is Badaowan group and Sangonghe group,the sequence ? is the Xishanyao group,the sequence ? is the Toutunhe group,and the sequence ? is the Qigu group.Sequence I includes lowstand systems tract,transgressive systems tract,high water system tract and regressive system tract;Sequence II includes transgressive systems tract,high water system tract and regressive system tract;Sequence III includes transgressive systems tract,high water system tract and regressive system tract;Sequence IV only retains the regressive system tract.On the basis of stratigraphic division,sedimentary facies studies were carried out.The formation of Jurassic in Fengcheng area in addition to fan delta and lake facies;further divided into four subfaciesIn the Jurassic strata,in addition to the fan delta facies and lacustrine facies are identified in the Fengcheng area,and further divided into four subfacies,fan including delta plain,fan delta front,shore shallow lake,half deep lake;and six kinds of sedimentary microfacies water distributary channel,water distributary interchannel,underwater distributary channel,underwater distributary interchannel,argillaceous shallow lake,sandy shallow lake.Based on the comprehensive analysis of the lithology,logging and seismic data of the man wells in the study area,the sedimentary characteristics of Fengcheng area are studied deeply.The spatial distribution and variation of the sedimentary facies are understood more clearly by analyzing the sedimentary connected well sections in the study area.Through the multi-attribute neural network analysis,the sandstone isometric graphs of each group are obtained to determine the phase boundary.According to the analysis,the following conclusions can be drawn:In the early stage of sequence ?,a certain degree of uplift occurred and the climate was humid,in the study area,Coal-containing coarse-grained sediments were found in the study area,and fan delta plain sediments and fan delta front deposits were developed in the study area.In the late stage of the sequence,the study area began to lake transgression,the lake became larger and fan delta front sedimentation quit,lake phase occupied as the main body.During the sequence ? period,the lake basin atrophied,the water body begins to become shallow,and fan delta front,the lake and the shallow lake sediments were developed.In the sequence ? stage,the northern part of the continuous uplift led to the absence of the northwest direction of the formation,the piedmont is mainly fan delta sedimentary,and the former large lake deposits withdrew and turned into fan delta front sediments,and fan delta plain deposition were developed in the southwest and northeastern;Sequence ?,most of the study area suffered a certain degree of erosion,leaving only the transgressive systems tract,mainly were fan delta plain and front subfacies. |
PDF Full Text Request