Gas-Bearing Prediction Of Tight Sandstone Based On Frequency-Division AVO Technique

The Jurassic Shaximiao Formation in central Sichuan is an important formation for tight gas exploration and development in the Sichuan Basin,with significant research value and development prospects.The geological characteristics of the study area are complex,and the accuracy of conventional AVO analysis methods in predicting the distribution of gas bearing properties of reservoirs is relatively low.In order to make the prediction of gas bearing properties of the Shaximiao Formation in the Qiulin area more accurate,and make exploration and development more targeted.This study is mainly aimed at the Shaximiao Formation in the Qiulin region.Through comparative analysis of the study area using wavelet transform,frequency division AVO,and full frequency band,it makes the prediction of gas bearing distribution more accurate.AVO analysis is one of the advantageous methods for predicting oil and gas,and AVO forward modeling and AVO inversion are the key links for predicting oil and gas.Through a large amount of study and research on AVO related literature and data,the author systematically describes the Zoeppritz equation,and based on this equation,carries out AVO forward modeling analysis for the study area,extracts the well side channel vibration frequency spectrum of the target layer,and finds the dominant frequency band of the target layer,Analyze the AVO response characteristics of the target layer using P-G intersection map features,use wavelet transform to perform frequency division processing of prestack data,and combine the dominant frequency band with the gather data for AVO attribute analysis.Carry out frequency division AVO attribute inversion,extract the dominant frequency and frequency division AVO negative anomaly attributes,and select gas sensitive factors for comparison.Select the AVO attributes of the dominant frequency band for fusion to build a gas bearing factor,Further,the distribution prediction of favorable gas bearing enrichment zones in the Shaximiao Formation in the Qiulin area is carried out.The research results indicate that the dominant frequency band of the gas layer is determined to be 25-30 HZ,with a main frequency of around 28 HZ,and the dominant frequency band of the dry layer is 30-35 HZ,with a main frequency of around 32HZ;Using the P-G intersection plot to analyze the AVO response characteristics of the target layer,within the frequency range of 30-35 Hz,the difference in response between the gas layer and the dry layer is the largest,and it increases with frequency;AVO forward simulation analysis shows that typical well gas bearing sections mainly exhibit Class III AVO response characteristics,while typical well dry layers mainly exhibit Class II AVO response characteristics;The difference in AVO response between the dominant frequency band and the full frequency band is more significant;The comparison between well and earthquake shows that the gas bearing prediction effect of AVO attribute in the dominant frequency band is good.