Study On Forward Modeling And Estimation Method Of Gas Hydrate Reservoir Saturation With Fractures

In recent years,traditional energy can no longer meet the needs of people's future production and life.In order to meet the increasing energy demand,natural gas hydrate,a new type of energy,has gradually become one of the research hotspots.With the continuous improvement of exploration and development means,the rapid development of petrophysics theory and natural gas hydrate research,the research of natural gas hydrate has gradually deepened,and has entered a new stage with the goal of commercial exploitation.The South China Sea is rich in natural gas hydrate reserves.During drilling and coring,it is found that there are visible hydrates in fractures,such as vein,block,nodule,and dispersed hydrates filled in pore space.Among them,fracture type hydrates can cause anisotropy of reservoir seismic data.In this paper,two end member layered media models are used to simulate hydrates in fractures and saturated water porous media.The elastic parameters of sediments in saturated water porous media are calculated by simplified three-phase Biot model.Through forward modeling of reservoir physical property characteristics,the relationship between reservoir property parameters and hydrate saturation and fracture dip angle can be understood,which can provide basis for subsequent estimation of hydrate saturation and dip angle.In order to verify the method and program,the fractured hydrate reservoir model is constructed,and the forward inversion of the saturation and fracture dip angle of the reservoir model is carried out to judge whether the inversion results are consistent with the constructed model.Based on the streamer data and the petrophysical model,the saturation of fracture filled hydrate reservoir is estimated by P-wave velocity,and the spatial distribution of hydrate is studied.For fracture filled gas hydrate reservoir,the most sensitive physical parameters to fracture dip angle change and hydrate reservoir response are P-wave velocity and P-wave impedance.The inversion results of the model data are in good agreement with the input parameters,which verifies the reliability of the method and the correctness of the program.Joint inversion of reservoir fracture dip angle and hydrate saturation by P-wave and S-wave can constrain the inversion results and reduce the influence of multiple solutions of seismic inversion.In the Northern South China Sea,the dip angle of fractured gas hydrate reservoirs ranges from 40° to80°.