Seismic prediction technology for complex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin:a case study of Jiaotan1 well area
The high-energy granular beach facies dolomite reservoirs are widely developed in Lower Permian Maokou Formation in central and northern Sichuan Basin.In this region,the gas production detected in Maokou Formation of Well Jiaotan1 can reach 112.8 × 104m3/d,demonstrating significant potential for oil-gas exploration.This paper is a case study of the representative Jiaotan1 well area in central and northern Sichuan Basin.Based on the geological characteristics,well log response,and seismic reflection analysis of Maokou Formation reservoir,it is believed that there are 2 major difficulties in reservoir prediction.Firstly,the heteroge-neity of beach facies dolomite sedimentation is strong,and it is difficult to predict the sedimentary boundaries;secondly,there is small difference in physical properties between the reservoirs and wall rocks,as a result of which the response characteristics of the reservoir are not obvious and it is still influenced by the seismic reflection of Maokou Formation top interface.Therefore,the paper proposes a set of seismic prediction techniques suitable for complex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin.Initially,efforts are made to restore the ancient landforms and determine the sedimentary zones of beach facies.Then,within the favorable facies zone,the seismic response of beach facies dolomite is clarified based on forward simulation,and further the seismic waveform and amplitude attributes are analyzed using the strong seismic event removal methods,thus deter-mining the development area of beach facies dolomite.Additionally,using the development zone of dolomite as the facies control con-dition,prestack inversion is carried out to characterize the planar distribution of the reservoir.Finally,based on the development characteristics of faults in Maokou Formation,a comprehensive evaluation is performed on the reservoir.This technology includes 3 main methods and relevant understandings as below.(1)A phase reconstruction method based on spectral decomposition is adopted to accurately identify the weak reflection lithological interfaces in Maokou Formation and improve the accuracy of paleogeomorphic restoration.(2)The recognition that waveform structure can reflect the development of beach facies dolomite in Maokou Formation is proposed,and its planar distribution is characterized using the attributes of wave trough number.(3)An optimized matching tracking method will be used to accurately remove the shielding effect of strong seismic event at Maokou Formation top interface on reservoir response.Based on the research results of this technology,the tested gas production of two wells is greater than 100 × 104m3/d,and the predicted reservoir thickness and logging interpretation error are less than 5 m,effectively solving the difficulty of predicting com-plex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin.
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