Research On Sedimentary Characteristics Of Shahezi Formation In Qinjiatun Oilfield-Shiwu Eight Well Area-Taipingzhuang Structure Region In Lishu Fault Depression

Lishu Fault Depression is situated in the Southeast uplift of Songliao Basin,which is divided into four tectonic zones,namely central structural zone,southeast slope zone,north slope zone and west fault-fold zone,and petroleum exploration began in Lishu Fault Depression from 1980s.The study area Qinjiatun oil and gas field is situated in southeast slope zone and Shiwu eight Well Area and Taipingzhuang Structure Region lies in central structural zone.Currently major strata in oil & gas assemblage in southeast slope zone and central structural zone are Denglouku Formation and Quantou Formation of Cretaceous,but deeper layers such as Shahezi Formation is still the major exploration and exploitation stratum in the future. According to high resolution sequence stratigraphy combined with sedimentology theory,on the basis of precise analysis of cores,well logging curves and seismic data,this dissertation provided a detailed stratigraphic division and correlation of Shahezi Formation,meanwhile sysmatically showed research on sedimentary characteristics of Shahezi Formation in the study area and its relationship with hydrocarbon accumulation. Conclusions were drawn as follows:(1)With geological and geophysical methods combined,this dissertation used horizon calibration T41 and T5(or T42) of Seismic Data to define the lower and upper boundary of Shahezi Formation;used the top mudstone with high values of GR curves of log interpretation as marker bed between Shal member and Sha2 member,the curve step of GR and AC as marker bed between Sha2 member and Sha3 member.The strata in Qinjiatun oil and gas field and Shiwu eight Well Area is divided into three members,and that in Taipingzhuang Structure Region is divided into two members and lack of Shal,due to depositional hiatus when on structural high part.(2)By synthesizing the characteristics of cores observation, analysis of lithological facies,logging facies,single well facies, multiple well facies and sedimentary evolution and models,combined with contour maps of sandstone thickness and sandstone thickness/strata thickness ratio,sedimentary facies maps,this dissertation showed research on sedimentary characteristics of Shahezi Formation in the study area.Results showed that the study area is mainly lacustrine-delta system(including fan delta,braid river delta,meandering river delta),and includes ten subfacies and 21 microfacies in all.There are three provenance systems,namely southeast provenance systems in Qinjiatun oil and gas field,northeast provenance systems in Shiwu eight Well Area and north provenance systems in Taipingzhuang Structure Region,while in the west of the study area is shallow lake-semideep lake in that time.(3)On the basis of sedimentary characteristics of Shahezi Formation in the study area, combined with analysis of structural characteristics, fault activity period and sequence,sandstone and sandy conglomerate develop very well in Qinjiatun oil and gas field and Taipingzhuang Structure Region,but strata in those two areas are buried not so deep that dark mudstone cannot generate hydrocarbon.Oil and gas may come from the west depression. Hydrocarbon migration channel could be sand bodies with good connectivity and unconformity surfaces.Hydrocarbon was migrated via a long distance and then formed mainly structural reservoir.Comparatively, Shahezi Formation in Shiwu eight Well Area was in structural low part when deposited,which made its sedimentary characteristics obviously different from the other two.Its depositional system is maily lacustrine system and easy to form structural-lithologic reservoir.