Diagenetic Characteristics Of The Tight Reservoir And The Favorable Exploration Area Forecast Of Gaotaizi Tight Oil Layer In Qijia-Gulong Sag

With the continuous development of high quality reservoirs in Daqing oilfield and the increasing demand for oil and gas resources,the development of unconventional oil and gas has been paid more and more attention as the main choice of oil production increasing.The 2 and 3 member of Qingshankou Formation in Qijia-Gulong Sag,that is,the Gaotaizi oil layer.The interlayer of sandstone and mudstone is widely developed,and the source rock and reservoir are integrated.It belongs to the typical tight oil.In this paper,the model was established to predict the porosity and diagenetic stage of the reservoir,and to further predict the favorable exploration area of the Gaotaizi oil layer,by analysis of composition,structure,cement content,pore throat characteristics and diagenesis of rock.The paper mainly studied the evolution stage of diagenesis,pore throat characteristics,composition characteristics,diagenesis numerical simulation,porosity prediction,pore structure prediction and favorable exploration area prediction.The method,including inclusion homogenization temperature,vitrinite reflectance,pyrolysis Tmax,XRD,the common thin section,cast thin section analysis,mercury injection experiment,were used in the paper.In addition,this paper studied the ostracod layer lithology characteristics,physical characteristics and oil-bearing characteristics,and predicted the favorable exploration area.It was observed from the microscopic chip,the lithology of the Gaotaizi oil reservoir was dominated by lithic arkose and lithic sandstone.This led to the weak compaction ability and easy dissolved ability of the reservoir.The main types of interstitial materials are clay minerals and carbonate,and the main types of cementation are pore type,contact type and secondary growth.The sedimentation and diagenesis of the reservoir have obvious control effect on the physical property of the reservoir.Three abnormal high pore zones are developed in the research area,and the bottom boundary depth of abnormal high pore zone is about 2350 meters.In this paper,the diagenesis of mudstone and sandstone was analyzed and the diagenetic stage was divided,and the rule of diagenesis in the whole area was discussed.It was founded that the diagenesis from the edge to the sedimentary center is constantly stronger.Base on the analysis of the rock forming field in the study area,the suitable model was selected to simulate the history of rock formation for the prediction of favorable areas.In addition,the influence factors of the reservoir physical property were also studied,the effect of diagenesis on the physical property of the reservoir is more important.The distributions of the tight reservoir of different geological ages in the Gaotaizi oil layer were predicted in the space and time domain by using the diagenetic numerical simulation technique and the porosity prediction technique.It is found that the area of the tight reservoir increased with the increase of the deposition time,and is mainly distributed in Qijianan area.Based on investigating the prediction methods of permeability,The permeability prediction model was selected and modified.The permeability of tight reservoirs in the taizingzi reservoir was predicted.The distribution of permeability contour is annular,and the permeability from source to sedimentary center decreases exponentially.Based on confirming the reservoir-forming time and tight time of the reservoir,the tight reservoir of the Gaotaizi oil layer was divided into two types,‘pre-accumulation and densification' and ‘pre-densification and accumulation'.The favorable exploration area of ‘pre-accumulation and densification' is similar to the conventional reservoir,so as to find a favorable trap for the high part of the reservoir.The favorable exploration area of ‘pre-densification and accumulation' is the low part of structure.Combined with the prediction results of reservoir porosity and permeability,the tight reservoirs in Qijianan area was divided into the most favorable areas,favorable areas and relatively favorable areas.