Research On Prediction Methodology Of Tight Reservoir Sweet Spots

In recent years,with the continuous progress of oil and gas exploration technology and the popularization of conventional exploration nationwide,it is difficult to make a big breakthrough in conventional oil and gas exploration.In order to deal with the increasingly tense international energy situation and China’s growing demand for oil and gas resources,unconventional oil and gas exploration has attracted wide attention and gradually become an important means to ease the energy tension and improve China’s energy structure.As an important part of unconventional oil and gas resources,tight reservoirs are widely distributed in Bohai Bay,Junggar,Songliao,Sichuan,Ordos and other basins.Tight reservoirs are often composed of tight sandstone and carbonate rock,with low porosity,low permeability,complex pore structure and no natural productivity.In the process of exploration and development,it is often necessary to implement a variety of fracturing techniques to achieve reservoir stimulation,in order to obtain industrial oil and gas flow.Therefore,it is significance for the exploration and development of tight oil and gas reservoirs to find out the "sweet spot" with good local porosity and permeability and conducive to fracturing when the general reservoir physical properties are poor.Sweet spot prediction has always been an important process in the exploration and development of tight oil and gas reservoirs.In order to find the area with good porosity,permeability and high oil and gas saturation in tight reservoir,experts and scholars of domestic and abroad have done a lot of research.However,for tight reservoirs,it is not comprehensive to only consider the physical properties of the reservoir.The engineering characteristics such as in-situ stress distribution and brittleness are also important guiding indicators for reservoir evaluation.Based on these parameters,we can find out the area which is easy to be fractured,that is,the engineering sweet spot,which plays a significant role in improving the production efficiency of tight oil and gas reservoir.Based on the characteristics of "double sweet spots"(physical property sweet spot and engineering sweet spot)of tight reservoirs,this paper not only looks for high-quality reservoirs with good porosity and permeability,but also considers the fracability of reservoirs.First of all,through the analysis of rock-physical experiments,this paper establishes a rock-physical model connecting seismic elastic parameters and reservoir physical parameters.A new AVO approximate equation is constructed by combining the obtained rock-physical model with AVO(amplify versus offset)technique.The equation is applied to prestack seismic data to realize the direct inversion of reservoir physical parameters and improve the prediction accuracy of physical parameters.Secondly,by studying the composition of in-situ stress,the prediction model of in-situ stress is constructed.At the same time,various prediction methods of brittleness are analyzed,and the prediction method suitable for large-scale survey area is optimized.Through prestack seismic inversion,the Young’s modulus,Poisson’s ratio and other related elastic modulus are obtained,the in-situ stress and brittleness of the survey area are predicted,the evaluation indicator of fracability is constructed,and the prediction of reservoir engineering sweet spot is realized.Finally,the distribution characteristics of double sweet spots in the survey area are comprehensively analyzed to realize the sweet spot prediction of tight reservoirs.