Frequency-domain Attributes Analysis And Seismic Identification Of Liuhua Reef Carbonate Reservoir

Reef carbonate reservoir has been a focus of petroleum exploration for their largeabundance and high capacity. Most of oil and gas discoveries in northern South ChinaSea（SCS）are located in Neogene, and reef oil-gas field is the bright spot inside thearea. Carbonate platforms were widely distributed throughout the Dongsha uplift inCenozoic. The autochthonous reefs grew above the platform have turned intoexcellent reservoirs due to holes and cracks developed inside and the blocking ofoverlying mudstone. LH11reefs on the Dongsha uplift is the largest oil fielddiscovered in recent years in our country among those reservoirs with the same type.But as a kind of typical structural-lithologic reservoir with high heterogeneity andintense concealment, it is often difficult to identify on conventional seismic sections.Previous studies have shown anomalies of reef with extracted spectral attributes. Thisstudy starts by trying to figure out the connections in between.Based on regional geological settings, this thesis reviewed the platformdevelopment and reservoir characteristics of carbonate on the Dongsha uplift, andthen discovered that the reservoir there were generally thin referring to well log data.The inconsistence of the oil-water interfaces inside the reservoir and the severefluctuation of porosity curve revealed the serious heterogeneity inside the reservoir.Three horizontal layered reservoir models have been developed according to thissituation. And spectral attributes analysis have been processed on the syntheticseismic sections acquired from viscous-elastic wave equation modeling. The resultsshowed that rhythm-type bedding may pull up seismic frequency with no significantattenuation.―Low frequency shadow‖(LFS) could hardly be detected underneath thereservoir; While thick-layered model and thin interbed model resulted in conspicuousattenuation with dominant frequency sightly decreasing, and it is clear to see LFSbeneath the reservoir, however, more sophisticated technique(HHT) of spectraldecomposition is required. After summing up the seismic response of reef carbonate platform in the studyarea, akin attributes were then analysed. The top of the reservoir had high attenuationwhich led to significant decrease of centroid frequency, but LFS were failed todetected underneath the reservoir on the common-frequency section. It is inferred thatthe reservoir were too thin to take substantial absorption and bring about abnormalfrequency decrease. However, the thin-bed tuning effect gave rise to the greatamplitude response when it was tuning frequency and also raised up the seismicfrequency. The previous conclusion could be used in reservoir thickness prediction.