Study Of Geophysical Response And Reservoir Prediction Of Deep Volcanic Rocks

In recent years, oil and gas exploration of volcanic rocks in deep layer, Songliao basin, has got a greatbreakthrough. Large volcanic gas reservoirs have been discovered one after another. Compared with theother types of rocks, volcanic rock shows its distinctiveness and complexity in the aspects of rock mineralassemblage pore structure association, physical properties and so on, which lead to its distinctivegeophysical response. The seismic prediction techniques which are useful for sedimentary rocks and othersare not applicable for volcanic reservoir prediction. In order to carry out the effective identification ofvolcanic reservoir and its oil and gas accumulation with the application of seismic techniques to theextreme, and to improve the drilling efficiency, this project has been carried out. By means of many elasticparameter testing of volcanic rock samples, seismic wave field forward simulation of volcanic edifice andvolcanic strata, the study of the seismic response to volcanic reservoir and its influent factors is carried outsystematically, meanwhile, the seismic prediction techniques for volcanic rock and its reservoir areexplored.The rock physical analysis of volcanic samples shows that, the pore development in volcanic rocks isless affected by buried depth, and as the depth increases, there is no obvious decrease in pore. The lithologyof volcanic rocks controls pore development. The porosity of volcaniclastic rock developed better than thatof lava, and the porosity of acidic lava better than that of basic one. So, the reservoirs of explosive faciesare better than those of effusive facies. Volcanic density indicates the development degree of reservoirpores. Possion's ratio is sensitive to the fluid contained in reservoirs, and the reservoirs containing gasshow have a lower Possion's ratio. Relative to gas saturation, the elastic parameters show a stepwiseattenuation feature. All of this presents the elastic parameters only can identify the existence of gas layerqualitatively, can not calculate the gas saturation quantatively.The study of geophysical and geological modeling of factors influencing different volcanic apparatusand wave field forward modeling show convergence and divergence of reflecting wave caused by differentvolcanic apparatus with the same inner structure are not the same. And weak scattered wave does smallinfluence to the imaging of seismic profile. We can accurately identify volcanic apparatus by use ofgeometric properties. Scattered wave field and others create interactive effect of superposition andinterference, which cause disconnected phenomenon of the wave front surface. Fractures indicatecharacteristic of white vertical strips on viable density seismic profile. The volcano explosive effects createthe diversity of lithologies and the polytropy of stacking structures, which will result in strong scatteredwave field and present an unorderly reflection features on seismic profile. The attenuation of compressionalvelocity of gas bearing reservoirs is greater than water bearing ones. With regard to the attenuation oftransformed wave velocity, water bearing reservoir of which is greater than that of gas bearing ones. In thewave field with low frequency, the characteristics of low poission's ratio is the response of gas bearinglayer.Seismic interpretation techniques can effectively identify the volcanic edifice and volcanic strata andpredict volcanic reservoir and gas potential. With the tendency surface analysis, semblance analysis,amplitude slice and other seismic attributes, combined with the characteristics on seismic profile, thedistribution of volcanic edifice can be identified out effectively. Based on the reservation and interpretationof seismic waves, combined with spectrum decomposition technique, the distribution of volcanic rock andsedimentary rock can be divided out fast and effectively. Integrated seismic waveform clustering analysiswith volcanic lithofacies division in single well, the volcanic lithofacies can be distinguished out. The seismic interpretation of volcanic strata need to follow the way of "determining strata-finding thechannel-encircling the rock bodies-dividing periods-dividing circles", which is a method of seismicsequence interpretation of volcanic rocks. With the seismic attribute attraction and optimization ofinstaneous amplitude, phase, frequency and so on, with the well-seismic correlation analysis, thedistribution of favorable reservoir can be qualitatively predicted out. Combined poststack seismic inversionwith gas-water surface analysis, the distribution of gas bearing reservoir can be predicted out indirectly.Prestack seismic inversion can directly predict the distribution of gas bearing reservoir, which requiresseismic data with a high quality. The seismic frequency attenuation attribute and the seismic energy changeattribute of bio-phase media elastic wave can be used to detect the gas bearing property of volcanicreservoir directly and qualitatively.