Study On Reservoir Transportation System And Caprock Characteristics Of Mesozoic Yanchang Formation In Ordos Basin

In the process of oil and gas reservoir formation,the transport system and caprock play a vital role,which jointly restrict oil and gas migration.The specific migration path of oil and gas is related to the distribution and properties of transport media and caprock along the dynamic direction,and is finally determined by the combination of transport system and caprock.Predecessors have done a lot of research on caprock and transport system,but there are great differences in the research concept,content and focus of transport system and caprock.For the transport system,predecessors only considered the transport system in the secondary migration,and did not study the transport system in the primary migration,that is,the internal transport system of source rock.Secondly,previous studies are only limited to the part with the best transport capacity,and do not consider the importance of the combination of transport systems with good and poor transport capacity to restrict oil and gas migration.For caprocks,most predecessors only considered the caprocks of conventional reservoirs,and there was not enough research on the caprocks of different types of reservoirs under different migration conditions.Secondly,most of the predecessors focused on the rock type and property itself,and the research on the relativity of caprock is not enough.The caprock is not necessarily a tight stratum,that is,in the process of oil and gas generation and reservoir formation,the rock stratum with relatively poor physical properties or the reservoir with relatively good physical properties can become its caprock.Based on the conventional porosity and permeability test,permeability change test under various conditions and cast and fluorescent thin section test,this paper analyzes the rock structure and pore structure characteristics of two components with relatively good and relatively poor oil content in different rock formations,and obtains the evaluation basis of transport system and caprock.On this basis,it is classified according to the evaluation basis,and the characteristics of different types of transport systems and caprocks are summarized,and finally its distribution is preliminarily understood.The conclusions are as follows:In the source rock reservoir of Yanchang Formation in Ordos Basin,the transport capacity of fractures is the best.In the experiment,the average permeability of the sample after fracture is 41 times of the original value.Secondly,through experiments,it is concluded that the transport capacity of parallel layer of source rock reservoir is better than that of vertical layer,and oil and gas often migrate along the direction of parallel layer of source rock.This combination of good and poor transport capacity forms the transport system of source rock reservoir.For caprocks,the caprocks of source rock reservoirs are mostly mudstone,salt rock and other strata with poor physical properties and no hydrocarbon generation.In the sandstone and sandstone mudstone combination reservoirs adjacent to the source rock,the transport capacity from good to poor are fractures,sandstone with good physical properties,sandstone with poor physical properties and shale.The combination of good and poor transport capacity forms its transport system.As for the caprock,it is mainly the shale caprock with poor permeability,the sandstone caprock with dense cementation and the caprock formed by the combination of the two.For sandstone reservoir,through relevant data and experiments,it is concluded that the transportation capacity from good to bad is fracture,sandstone with good physical properties and sandstone with poor physical properties.The permeability ratio of sandstone samples after fracture and before fracture is more than 1,and some samples reach 178.57.This combination of good and poor transport capacity forms the transport system of sandstone reservoir.For the caprock,in addition to the traditional mudstone,salt rock and other types of caprock,there are also sandstone and sand layers with poor permeability and dense cementation,which can be used as caprock.This kind of mudstone,salt rock and other types of caprock act together with the slightly poor physical properties and tightly Cemented Sandstone caprock to form the caprock of sandstone reservoir.In the case of fault,that is,in the fault rock combination,the cores and thin sections with different oil content and relevant experiments and data show that in this case,the fault with the best transport capacity is located in the deep elastic-plastic section and fracture section,followed by the sandstone with the transport capacity worse than the above fault.This combination of good and poor transport capacity forms the transport system of fault rock combination.