Granite Reservoir Prediction Research Based On The Pre-stack Elastic Parameter Inversion

With the continuous development of oil and gas exploration,lithologic oil and gas reservoirs have become one of the main exploring target.The granite reservoir in the Bohai area is the largest buried-hill granite oilfield related to Mesozoic granite found recently in China.Because of granite's complexity and strong lateral heterogeneity,conventional seismic inversion method cannot meet the required precision in reservoir prediction.To improve the accuracy and reliability in granite reservoir prediction,this paper studied key techniques.And a set of granite reservoir prediction workflow based on the pre-stack elastic parameter inversion was proposed in Bohai area.The difficulties in the prediction of granite reservoir prediction include low quality of seismic data,systematic error of logging data,the lack of shear wave data,and little difference between reservoirs and non-reservoirs.According to this,four key techniques were proposed:(1)To improve the quality of seismic data,we based on the layer flattening proposed a optimization technology of pre-stack gathers by the combination of "energy compensation-flattening-cutting".(2)A partition log curve normalization workflow was proposed to eliminate systematic errors between so many logging data.(3)The method based on the equivalent matrix mineral bulk modulus theory and the dominant porosity theory was used to improve the precision of shear wave velocity.(4)We selected Poisson's ratio as the best reservoir prediction factor by analyzing the rock physics parameters of single well and multi-well.The above key techniques were applied to predict granite reservoirs in Bohai area,and a set of granite reservoir prediction workflow based on the pre-stack elastic parameter inversion was formed in this area.Pre-stack stochastic inversion method was used to extract elastic parameters,and Poisson's ratio was selected as the best reservoir prediction factor.At last,we analyzed the profile and plane characteristics of Poisson's ratio.By computation of practical examples,we draw the following conclusions:(1)We found that the inversion Poisson's ratio can not only identify the reservoir,but also can classify the reservoir reliably.(2)The distribution law of granite reservoir in the study area was obtained.Reservoirs mainly concentrated in the structure saddle where fracture develops,that is surrounded the study area.This is consistent with logging interpretation and geological knowledge.The analysis and application in study area shows that the proposed workflow for Bohai area can obtain accurate and reliable inversion results to predict granite reservoirs by combining seismic data,logging,rock physics,and geological data.What's more,the predicted results can effectively guide the subsequent exploration and development in the study area,and have important practical application value.