Study on the fine prediction of a marlstone reservoir in the Lei32 sub-member in Chongxi area,central Sichuan
Multiple drillings in the Chongxi area of the central Sichuan Basin have revealed good oil and gas indications in the marlstone reservoir of the Lei32 sub-member.There are widely developed layers of salt rocks on top of the marlstone in the Lei32 sub-member,and the impedance of the salt rock and marlstone reservoirs are similar.Indeed,reservoir predictions are difficult to make using conventional methods due to the strong wave peak shielding effect of the salt rock.To predict the lateral and vertical distribution of the marlstone reservoir accurately,we first used synthetic logging data to calibrate and clarify the geophysical response characteristics of the marlstone reservoir.Then,we conducted a physical analysis of the rock's lithology and the reservoir,selected sensitive parameters that can identify the salt rock and marlstone reservoir,used a seismic waveform indication simulation to predict the distribution of the salt rock,and finally used waveform inversion to predict the distribution of the marlstone reservoir.The results showed that the salt layer at the top of the Lei32 sub-member corresponded to strong peak reflection,and the bottom boundary of the reservoir corresponded to weak peak reflection.There was a significant overlap of impedances between the reservoir and the salt layer,however,the density of the salt layer differed significantly from that of other lithologies.After removing the influence of the salt layer,the impedances could be used to distinguish between reservoirs and non-reservoirs.Therefore,after using the waveform indication simulation to identify the salt layer,the seismic waveform indication inversion could effectively identify reservoirs.The reservoir in the Chongxi area is extensively developed,with a thickness of 30～60 m,containing 16 developed lithological traps,and covers a total area of 124 km2,which is a realistic area for searching for new limestone reservoirs.
central Sichuan BasinLei32 sub-membersalt rockmarlstone reservoirwaveform indication inversionwaveform indication modeling
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