VSP Interpretation Of Carbonate Reservoir Of 327 Well Area In Tuofutai

In the Tuofutai area of Tahe oilfield,the structure of Ordovician carbonate fracture-cavity reservoir is complex.A complex association of fractures and caves constitutes the reservoir space of the carbonate fracture-cavity reservoirs and the percolation ability and storage capacity of the matrix of such reservoirs are generally poor.Compared with porous or fractured reservoirs,fracture-cavity reservoirs are so complex that it is hard to delineate.Conventional ground seismic exploration is difficult to find out the inner details of Ordovician reservoirs,which data resolution can no longer meet the present demand of exploration and development.To provide more accurate predictions of reservoir properties of the Tahe Oilfield and to predict the inter-well connectivity,a walkaround 3D-3C vertical seismic profiling?VSP?survey was conducted.In this paper,based on the walkaround 3D-3C VSP data of Tuofutai 327 well area,we briefly introduce the method and principle of VSP pre-stack time migration imaging.We focus on the process of processing and interpreting VSP and ground seismic data by using seismic attribute extraction,spectrum analysis and joint inversion technologies.By joint interpretation of ground seismic and VSP data,we summarize the seismic properties of carbonate reservoirs,and describe the reservoir interior characteristics in detail.Finally,by using the attribute parameters such as PP-wave impedance,density and Poisson's ratio obtained by inversion,we predict the distribution of favorable reservoirs.The prediction results are verified using both logging and production data.By carrying out the above research,we obtain the following achievements and knowledge on the development characteristics of carbonate reservoir and the characteristics of VSP exploration in the Tuofutai 327 well area.1.The favorable reservoir in well Tuofutai 327 is mainly developed in the Ordovician Yijianfang and Yingshan formations.Since the T₇⁴ interface is an unconformable surface,the strata below the interface develop a large number of dissolved ditches and cracks due to the weathering and denudation which provide a good reservoir space for oil and gas.2.By comparing VSP and ground seismic data,it is found that VSP data have higher resolution,signal-to-noise ratio,higher main frequency information and wider spectrum range.In VSP inversion profiles,more abundant reflection characteristics of Ordovician strata can be observed.3.According to the attribute section,the distribution range of potential favorable reservoirs in the study area on the plane is delineated.The favorable reservoir area has a low PP-wave impedance and Poisson's ratio,and the whole area presents the characteristics of northeast–southwest banding distribution,which is consistent with the development morphology of the fault zone in this area.