The Research Of Seismic Reservoir Prediction In Suining Formation JSN₂² On LD Gasfield

The LD gas field is located on the gentle slope structural belt in the east of the West Sichuan Depression,adjacent to the west fault of the northeast-oriented structural belt in the north of Longquan Mountain.Reservoir lithology is dominated by brown lime fine sandstone,siltstone and muddy interbed,it belongs to lake-delta deposition in an oxidizing environment.Since 2000,LD gas fields have successively discovered gas reservoirs in the Jurassic Penglaizhen Formation,Suining Formation,and Shaximiao Formation.There are more than 150 wells drilled in the whole area,the proven geological reserves are12×10⁸m³,and the cumulative natural gas production is 1.16×10⁸m³,which has reached a three-dimensional and comprehensive development situation.As the development progress deepens,the rate of decline in production of old wells accelerates,and the overall output of the gas field is in a downward trend.Therefore,it is urgent to find new production blocks outside the main production layer.In this study,the seismic-geological mutual feedback method was adopted.Based on the analysis of sedimentary facies,seismic facies,and seismic attributes,based on the summary of previous research data,the plane distribution characteristics,tectonic characteristics and unfolding of sand bodies in the target layer of the study area were clarified.Seismic attribute characteristics,summarizing the seismic response characteristics of favorable regions in the study area,and predicting favorable blocks of JSN₂²gas reservoir of Suining Formation in LD gasfield.This study focus on the predictions of the JSN₂² sand group reservoir of the Suining Formation in the LD gasfield and selects favorable blocks.Because the reservoirs of the Suining Formation are mostly thin mudstone interbedded layers,they often overlap each other in the vertical direction and cannot be achieved by a single method.Accurately identify and finely evaluate the effect,therefore,using the integrated seismic-geological thinking,comprehensive application through a variety of methods,on the basis of stratigraphic calibration and interpretation of the J JSN₂²sand group of Suining Formation in the LD gasfield,select typical wells with complete logging data Synthesize seismic records,compile tectonic maps,identify structural features of the target layer,and simultaneously use well logs and seismic data to carry out single-well sedimentary facies analysis and continuous well sedimentary comparison,and identify target sedimentary facies zones in the study area with the help of seismic facies constraints To clearly define the dominant sedimentary microfacies and to accurately describe the distribution of river channels in the study area.Integrate the logging response characteristics and seismic response characteristics of the target layer,carry out seismic inversion,extract seismic attributes such as amplitude,frequency,wave impedance,coherence,etc.to analyze the target layer,and establish seismic reservoir evaluation standards.Comprehensive structural research,sedimentary facies research and seismic attribute analysis conclusions,establish comprehensive reservoir evaluation criteria,evaluate the JSN₂²sand group reservoir and select favorable blocks.This paper draws the following conclusions:?1?Identify the top of the JSN₂²sand group with the mudstone of the largest lake in the Suining Formation in the study area as the dividing line,carry out the calibration and interpretation of the target horizon,and compile a time-depth conversion to compile the structural map of the top of the JSN₂² sand formation in the Suining Formation in the study area.The overall structural feature is a northeast nasal anticline,and the tectonic trend takes over the upper strata.There is a northwestward groove between the LS40 well group and the L653 well group,and three structural high points are identified;?2?According to single-well sedimentary facies research and continuous well sand body distribution research,it is believed that the overall Suining Formation in the study area is a lake-delta sedimentary dominated by shore-shallow lakes,and the J JSN₂² sand formation has a variety of sedimentary microfacies,mainly underwater divergence The distribution of sedimentary facies belts in rivers,estuary dams,distant sand dams,mat-shaped sands,distributary bays,etc.are complicated in the horizontal direction,and are thin,layered,lenticular,or layered in the vertical direction.Among them,the microfacies of underwater distributary channels are Predominant sedimentary facies;compiling sedimentary facies maps combined with seismic facies constraints,and finally identified 5 river sediments,all of which are northwest-southeast,and the production wells are all located in underwater distributary rivers;?3?Based on the logging and seismic response characteristics of the JSN₂² sand group in the Suining Formation in the study area,it is believed that the GR value of the gas layer of the JSN₂² sand group is generally 50?60 API,the AC is generally60?70 us/ft,and the CNL measurement is generally 4?9%,DEN measured value is generally in the range of 2.2?2.55g/cm3,and RD measured value is in the range of35?120?m;seismic properties of high-quality reservoirs of JSN₂² sand group are low frequency,strong amplitude and low impedance;more favorable reservoirs are medium-low impedance,Medium-medium strong peak and valley amplitude,low frequency;poor reservoirs are characterized by higher wave impedance,weak amplitude,and high frequency;?4?Comprehensively consider factors such as the type of sedimentary facies,the distribution characteristics,structural characteristics,the distribution of sand bodies in connected wells,differences in seismic attributes of reservoirs,etc.,and The favorable facies zone in the study area is divided into three types:namely,type?enrichment area,type?favorable area,type?low-productivity area,and type?enrichment area in channel?5?.Well area LS41 has been built,with a length of about 2.4km,a width of about 330m,and an area of about 0.6km2.Its amplitude is higher?>33000?,frequency is lower?<40Hz?,continuity is good,and wave impedance is lower?<10760?,in line with the forecast model,with potential for production,with an estimated reserve of 0.77×10⁸m³.