Study On Gas Detection Methods For Deep Carbonate Reservoir

Carbonate rock is one of the most important types of natural gas reservoirs.Carbonate reservoir is an important reservoir space for oil and gas.Because of the old age of carbonate strata,deep burial,little difference between reservoir and nonreservoir physical properties,and no obvious seismic response characteristics of reservoirs,it is difficult to detect gas-bearing properties of deep carbonate reservoirs.The main content of this paper is the prediction and gas-bearing detection of carbonate reservoirs in Changxing-Feixianguan Formation of an exploration area in northeastern Sichuan,with the emphasis on gas-bearing detection technology and application research.The concrete results of the paper are summarized as follows:(1)This paper introduces the theoretical basis of various methods for gas-bearing detection of carbonate reservoirs.The theoretical basis of seismic dispersion analysis and AVO anomaly analysis is emphasized.The time-frequency analysis methods commonly used in dispersion analysis,such as S-transform,generalized S-transform and improved generalized S-transform,as well as the implementation process of various prestack inversion methods in AVO anomaly analysis are introduced in detail.(2)Taking an exploration area in northeastern Sichuan as an example,the sedimentary facies characteristics of the target formation in the study area are determined by seismic sedimentary facies analysis,and the P-wave impedance data volume is obtained by inversion based on the constraints,then the time-domain spatial distribution of reservoirs is obtained by using the impedance data volume calibrated by the petrophysical data in the well,and the reservoir thickness characteristics are obtained by high-precision time-depth conversion.Attribute analysis technique is used to obtain the spatial distribution characteristics of reservoirs,and coherence analysis,curvature analysis and stress field numerical simulation are used to study and obtain the structural characteristics of reservoirs.(3)The improved generalized S transform is used to analyze the seismic data volume of the target interval in the study area.The low frequency attenuation gradient is used to detect the gas-bearing property of the reservoir.This method has good application effect;AVO attributes such as intercept P,gradient G and Poisson's ratio are extracted from prestack seismic data.These attributes are distributed disorderly in profile and plane,and their practical application effect is poor;the multi-elastic parameters of target formation in the study area are obtained by pre-stack simultaneous inversion.A new elastic parameter,fluid identification factor,is calculated based on the petrophysical interpretation chart of gas-bearing reservoir obtained by petrophysical analysis in wells,which has a good application effect in gas-water identification.(4)The weighted fusion method is used to comprehensively evaluate the gasbearing reservoirs in the target formation of the study area.The reservoir thickness,Pwave impedance volume,dispersion analysis data volume and fluid identification factor data volume are weighted and fused.The gas-bearing property of the target formation is evaluated comprehensively by combining the sedimentary facies distribution characteristics,spatial distribution characteristics and structural characteristic fluid identification factors of the target formation reservoir in the study area,and finally the gas-bearing reservoir plane distribution in the study area is obtained.(5)A comparative analysis is made of various methods for gas-bearing detection of carbonate reservoirs.Among them,dispersion analysis calculation is simple,efficient and applicable;AVO attribute analysis is affected by strong heterogeneity of carbonate reservoir,and its application effect in deep carbonate reservoir is not good;single elastic parameter obtained by pre-stack inversion can not accurately predict the distribution of gas-bearing reservoir;fluid identification factor calculated by two elastic parameters,?×? and Vp/Vs,can predict carbonate gas reservoir more accurately and reliably.