| Tracer monitoring technology,as an important means of understanding formation conditions,can effectively judge the flow direction of formation fluid,heterogeneity between injection and production wells in well groups,and connectivity between wells,which can provide an important basis for enhanced recovery measures.At present,the interpretation technology of water soluble tracer in sandstone reservoirs is relatively perfect,but there are few gas tracer interpretation models for carbonate reservoirs.Moreover,a large part of the caves considered are smaller diameter caves,which can not meet the gas tracer interpretation requirements of large-scale cave reservoirs.Considering the geological characteristics of large scale karst caves in fractured-vuggy carbonate reservoirs in Tahe Oilfield,this paper establishes an interpretation model of gas tracer between wells in fractured-vuggy carbonate reservoirs,puts forward an interpretation method,compiles a software for gas tracer interpretation,and applies it to practical cases.The main research results of this paper are as follows:(1)A one-dimensional flow and two-dimensional diffusion model of gas tracer for fracture is established.Compared with the one-dimensional flow and one-dimensional diffusion model,the model considers the diffusion of tracer in the vertical direction of flow.The theoretical value of the former one,which is closer to the actual situation,is generally one order of magnitude smaller than that of the latter one with the same parameters.(2)A gas tracer radial seepage diffusion model for large-scale karst caves is established.According to the difference of theoretical curves between the model and the one-dimensional flow and two-dimensional diffusion model,a method for identifying whether there are caves in the channel is proposed according to the concentration gradient curve.This method can quickly identify whether there is a karst cave in the formation,and provide a basis for the choice of mathematical model in the interpretation of tracer concentration curve.(3)A gas tracer interpretation model for carbonate reservoirs with multi-fracture and large karst cave is established.The model considers one-dimensional flow and two-dimensional diffusion of tracer in fracture and radial flow and diffusion in Karst cave.It can explain the flow and diffusion of tracer in pure fracture,fracture-karst cave or Karst cave reservoirs.Sensitivity analysis using this model shows that the volume of large-scale karst caves has the greatest influence on the shape of the curve,and the length of cracks mainly affects the time when the concentration curve appears,while the influence on the shape of the curve can be neglected.(4)A method of using acoustic filtering to process the concentration curve of tracer is proposed.This method can effectively solve the problem that there are human factors in the identification of the number of flow channels.(5)Based on the model and interpretation method,combined with modern fitting algorithm and computer multi-threading technology,a well group tracer interpretation software is developed.The software can interpret the number of flow channels,the sweeping volume of fracture and the volume of karst cave between injection and production wells.The tracer concentration curve of X well group in Tahe oilfield is interpreted by using this software.The volume of karst caves between injection well and production well is 8845 m3,and there are three high permeability fractures.The distribution coefficients of them are 0.356,0.291 and 0.353.The gas sweep volumes of the1 are 769,644 and 722 13.The results are reasonable. |
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