Integrated Prediction And Evaluation For Natural Gas Hydrate Resource Of XN Study Area In The Northeastern South China Sea

Natural gas hydrate is considered as the most promising new energy source to replace conventional fossil fuels such as coal,oil and natural gas in the 21 st century,which is contributed to its abundant resources and high efficiency and cleanliness.However,as a result of different kinds of gas hydrate,such as block,vein,nodule,mass and thin layer,and the strong lateral heterogeneity of its distribution,which leads to a lot of uncertainties in the fine characterization of gas hydrate resources and the accurate calculation of resources.Recently,the Guangzhou Marine Geological Survey has carried out a large number of geological and geophysical surveys and drilling surveys in the XN sea area in the northeastern South China Sea.The accumulating abundant geological data provides a good opportunity to solve this problem.Based on geological and geophysical materials,the structural geology,sedimentary geology,sequence stratigraphy and geological theory of natural hydrophilic resource formation was combined in this study.Through detailed interpretation of seismic data and analysis of drilling and logging data,we achieved the following understanding.Based on a series of dynamic processes such as biogeochemical reaction of organic matter-methane-natural gas hydrate system in seabed sediments and dynamic transformation of water-soluble gas-free gas-natural gas hydrate,a numerical model of gas hydrate resource formation kinetics was established,which realized the coupling of macro basin evolution kinetics model and micro material transport-reaction kinetics model.The established evaluation system of "metallogenic condition analysis-pre-drilling prediction-post-drilling evaluation-resource calculation" of natural gas hydrateprovides a strong support for revealing the distribution law of natural gas hydrate and evaluating the favorable target of natural gas hydrate.The geological reserves of natural gas hydrate in the study area are estimated to be more than 100 billion cubic meters of natural gas,which is equivalent to the super large conventional gas field and has good resource prospects for future development of natural gas hydrate.According to the characteristics of resource,formation fluid extraction is considered to be one of the most suitable method for trial production,and it is also an effective way to achieve cost reduction,efficiency increase and safe development.In addition,this paper has also made innovative breakthroughs in the technology of fine characterization of gas hydrate resources.Based on the seismic attributes such as velocity,energy half-life,three instantaneous attributes and AVO,combined with OBS shear wave variation information,combined with post-stack impedance inversion without well and pre-stack simultaneous inversion without well,a set of pre-drilling prediction methods for natural gas hydrate ore bodies has been formed to quantitative.The simulation results show that the inversion results of log-constrained sparse pulse wave impedance have good resolution and prediction accuracy.Random simulation inversion makes full use of the advantages of vertical high resolution of logging data and lateral high resolution of seismic data to further improve the vertical prediction accuracy of ore bodies.The combination of the two inversion methods can more accurately delineate gas hydrate resource model which provides technical support for post-drilling evaluation of natural gas hydrate.At the same time,the comparative study of porosity and saturation interpretation model shows that density porosity,acoustic porosity model and dual water saturation model are suitable for logging interpretation model in this area,and provide a strong guarantee for accurate calculation of important physical parameters such as porosity and saturation of gas hydrate resource.The above geological understanding,theory and innovation of technical methods comprehensive predicts and evaluates of natural gas hydrate resources in the study area.By comparing actual drilling and test results,the method systemof before drilling integratedprediction and post-drill evaluation is built inthis paper,which also provides scientific basis for further exploration and post-development in this area.At the same time,it can also provide reference for the comprehensive prediction and evaluation of gas hydrate resource in other sea areas,so as to achieve the purpose of improving exploration effectiveness,reducing exploration risks and reducing exploration costs..