Research On Formation Conditions Of Tight Oil In Ordos Basin

Yanchang Formation in Triassic Ordos Basin contain considerable large amount of dense oil.In this study,I analyzed the formation of the dense oil from the respects of source rock,reservoir property and relation of source and reservoir,evaluated the properties of the dense oil,select favorable zones and set up a comprehensive evaluation indication system,make comprehensive assessmentm with Analytic Hierarchy Process(AHP)and double factors method.Reviewing the development of exploring dense oil over the world,the porosity of dense oil reservoir is commonly less than 12%,the permeability is 0.1~1 md and without a migration of long distance.Yanchang Formation reservoir is mainly composed of dense sandstone,we take Long Dong region as an example,study the formation condition of dense sandstone oill.There are two types of source rock in the Mid and Lower Yanchang Formation,Chang 7 oil shale and Chang 4+5 and Chang 9 dark mud stone.With a high organic carbon content and high maturation,the oil source rocks are widely distributed.With a complicated porosity texture and mostly secondary developed,the reservoir contains a relatively large amount of feldspar lithic fragments and located in underwater distributary channel of the delta front and sands of non-gravity flow around hydrocarbon generation center,have a good conection with source rock.The main cause of the formation of dense reservoir in Yanchang Sandstone of Long Dong region firstly is the middle to strong compaction,and secondly is the cementation.Clarified the relationship between the compaction and the cementation,think the differentiated compaction in the early stage was followed by mass hydrocarbon accumulation in general.The perspective beneficial region of the compacted sandstone reservoir was selected based on a map of the Yanchang Sandstone distribution overlaid by the distribution of the effective source rock.The effective region of Chang 8 dense oil is mainly located in the northwest and the southwest,and the effective region of the Chang 7 dense oil is mostly in Huachi,while Chang 6 dense oil has well spread effective region.Combined the mineral resources planning requirement and current status of dense oill in Erdos Basin,we make comprehensive assessent system for dense oill from exploration and development,including source condition and extemal conditions(such as landforms,fracturing).The entire region was divided into Priority Exploring Region,First Class Exploring Region,and Potential Exploring Region based on the evaluation of both of the exploring and development and the research status of the Ordos dense oil by double factors method.The Priority Exploring and development Region are all located in southwest and Mid Lake area.