Abstract:Gas hydrate has different filling modes.It can be a part of pore fillings or a component of solid matrix in strata.So,the rock physical model of gas hydrate is quite different from conventional rock physical models for oil and gas,and conventional S-wave velocity prediction method is not suitable for gas hydrate.Pertinently,a method to predict S-wave velocity of gas hydrate based on effective medium model was proposed in this paper.Firstly,the influence of mineral composition,porosity and hydrate saturation on P-wave and S-wave velocities was analyzed.Secondly,according to the effective medium model,a constrained optimization equation was established based on the conventional well log data such as P-wave slowness,density,shale content,porosity and saturation.The optimization equation was constrained by conventional log data such as P-wave velocity and density,porosity and saturation were used as optimization variables to find the optimal solution.The trust-domain algorithm was applied to solve the constrained optimization equation with fast convergence rate and reliable calculation results.Finally,the efficiency of the proposed method was proved by the drilling data of gas hydrate in Shenhu area,Northern South China Sea.The results of S-wave velocity and saturation match real data well.
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