Research On Sedimentary Facies And Favorable Reservoir Sandbodies Of Putaohua Reservoir In Southwest Qijia-Gulong Depression

Putaohua reservoir in the southwest of Qijia-Gulong sag is located in the west of Daqing placanticline in the north of Songliao Basin.It contains many structural units.The secondary structural units include Qijia-Gulong sag and Longhupao Daan terrace,covering an area of more than 400 square kilometers.The predecessors have been exploring the area west of Daqing Placanticline in Songliao Basin for more than ten years.However,the study on sedimentary assemblages of the Northern Lake Basin and shallow water delta in Songliao Basin is relatively thin.There is no clear conclusion on the definition of precise stratigraphic sequence division,the establishment of high-resolution sequence stratigraphic framework and the prediction of favorable reservoir sand bodies.In this paper,the sedimentary system and favorable reservoir sand bodies of Putaohua reservoir in southwestern Qijia-Gulong sag,Songliao Basin are studied in detail.The research contents have important guiding significance for energy exploration and development in northern Songliao Basin.Guided by the theory of high resolution sequence stratigraphy and sedimentology,the sequence stratigraphy and sedimentary facies of Putaohua Oil Reservoir in southwestern Qijia-Gulong Depression are studied comprehensively by using seismic,core observation,logging and other data in the study area.The high resolution sequence stratigraphic framework of Putaohua reservoir was established,and the plane distribution,spatial evolution and favorable reservoir sand body characteristics of sedimentary facies in the sequence stratigraphic framework of the study area were analyzed.Through accurate identification of sequence boundary markers,the sequence stratigraphic framework of the study area is established.In the sequence framework,the plane distribution of sedimentary facies and the distribution characteristics of favorable sand bodies are analyzed.The research draws the following conclusions:(1)The identification marks of sequence boundary in the high-resolution sequence stratigraphic framework of Putaohua reservoir in southwestern Qijia-Gulong sag are established,and the high-resolution,high-precision sequence stratigraphic framework and fine stratigraphic database of Putaohua reservoir in southwestern Qijia-Gulong sag are established.(2)Using fine core observation and description,it is confirmed that the shallow delta front subfacies developed extensively in various periods within Putaohua reservoir in southwestern Qijia-Gulong sag,followed by shore-shallow lake deposits.(3)Analysis of vertical sedimentary facies profile characteristics of Putaohua reservoir in southwestern Qijia-Gulong sag shows that the vertical evolution of sedimentary facies in Putaohua reservoir is that the sedimentary water body gradually changes from shallow to deep,reflecting the lake transgression sedimentary process as a whole.(4)The stratigraphic profile and sedimentary facies plane distribution characteristics of Putaohua reservoir in southwestern Qijia-Gulong sag are analyzed in detail.Generally speaking,the channel sand bodies of Putaohua oil reservoir in southwestern Qijia-Gulong sag are characterized by strong heterogeneity of sand body distribution,small thickness variation,good connectivity,and the shape of encircling lakes in a ring.(5)Sedimentary characteristics of favorable sand bodies in Putaohua reservoir in southwestern Qijia-Gulong sag are summarized.The types and scales of favorable sand bodies are analyzed.The main favorable reservoir sand bodies of Putaohua reservoir in the southwestern part of Qijia-Gulong sag are underwater distributary channel sand bodies,which spread from west to East and are mainly controlled by short-axis provenance in the West and have strong heterogeneity.