Sedimentary Facies And Sand Body Distribution Of Chang 7 Oil Reservoir Group In Heshui Area

This paper takes the Chang7 oil reservoir group of Yanchang Formation in Heshui Area of Ordos Basin as the research object,Summarizing the previous research results.Using theories and methods of sedimentology,stratigraphy,and well logging geology.Based on the field outcrop,core and well logging data,This paper systematically studies the strata,provenance,sedimentary system,gravity flow sedimentary characteristics and petroleum geological significance in Heshui Area.In order to clarify the formation characteristics of the study area,it is divided into Chang7₁,Chang7₂,and Chang7₃.From the perspectives of light and heavy mineral assemblage and paleocurrent analysis,combined with the characteristics of the surrounding paleocontinent,the provenance of the Chang 7 oil reservoir group in the Heshui area is studied.The results show that the study area is jointly influenced by sources from the southwest,south and northeast directions.Through the analysis of rock color,sedimentary structure,rock structure,paleontology and logging facies,it is considered that gravity flow sediments developed in the semi-deep lake—deep lake background during the Chang 7sedimentary period in the study area.Guided by the theory of sandy debris flow,four types of gravitational flow genetic types were identified in the study area:slump deposition,sandy debris flow deposition,argillaceous debris flow deposition,and turbidity current deposition.The Chang 7 gravity flow sedimentary facies in the Heshui area are divided into two types:sublacustrine fan,and deep lake plain.The sublacustrine fan includes three subfacies including inner fan,middle fan and outer fan.Distant source channels and overflow banks are developed,and lobe microfacies are developed in outer fans,and various microfacies correspond to their genetic types.The evolution law of sedimentary facies and the distribution law of sand bodies were further studied vertically,horizontally and horizontally,6 types of sand body superposition styles are identified,and the establish Chang 7 gravity flow deposition model in the Heshui area.Provenance and triggering conditions are the main controlling factors affecting the development of gravity flow sediments.By counting the porosity and permeability characteristics of each microfacies of gravity flow deposition and analyzing typical wells,it is believed that each microfacies of gravity flow deposition has different reservoir characteristics,and the channel sand body has the most high-quality reservoir development characteristics,followed by overflow and lobe sedimentary sand bodies,and the distribution of sand,mud,sand and mud in slump sediments is poor,making it difficult to develop high-quality reservoirs.The deep-water gravity flow sand bodies of the Chang7 oil reservoir group in the Heshui area are vertically superimposed with the source rocks,forming a reservoir with near-source advantages.