Construction Of Petrophysical Model Of Gas Hydrate Formation And Speed Prediction Based On Genetic Algorithm

The identification of the natural gas hydrate reflecting characteristic and the quantifying extraction of the physical property information exist multiplicity and uncertainty,petrophysics mainly studies the relationship between reservoir characteristics and earthquake response,and it is a bridge between reservoir parameters and rock elastic parameters.Petrophysics model construction is a bridge to quantitatively transform earthquake information from geophysical observations of hydrate formation into physical property information,rather,traditional petrophysics model merely has description about micro pore structure and pore filler.This paper particularly consider the micro structure of the hydrate formation which is subject to hydrate formations of particle support and pore filling these two distribution model,which is based on the equivalent medium theory and Gassmann theory,two kinds of physical models of hydrate formation and its model,and analyze the sensitivity factors under different conditions.On this basis,introduce variable parameters,and construct variable dry rock framework equivalent physical model,and combine it with genetic algorithm adaptive inversion of equivalent elastic modulus to further realize the prediction of reservoir shear wave speed.Particle support model and pole filling model are two basic models,they analyze from two angles of different poles and different pole aspect ratio,and concluded that the longitudinal wave and transverse wave speed decrease with the increase the porosity,and increase with the increase of the hydrate saturation;the longitudinal wave and transverse wave speed increase with the increase of the pole aspect ratio,the pole aspect ratio is more small,the longitudinal wave and transverse wave to the hydrate saturation is more sensitive;Totally speaking,the particle support model is sensitive to the transverse wave,and the longitudinal wave speed can be as a sensitive factor to provide help to later analysis.Make use of the variable dry rock framework equivalent model and genetic algorithm can effectively predict the transverse speed.On the basis of the elementary model,introduce the adjustable parameters and substitute differential equivalent medium equation,and further simplify the derivation of special shape inclusion(round shape,coin shape needle shape)and the equivalent rock physics model of arbitrary aspect ratio ellipsoid shape inclusions to make the model more flexible and applicable.As for the high prediction accuracy of dry rock framework equivalent model quantity,it can be combined with Gassmann equation to evaluate the transverse speed of rock.This paper further consider the the influence of pole geometric shape and other factor to the formation speed,when combined with genetic algorithm adaptive evaluation equivalent elastic modulus,it improves the accuracy of the transverse wave and makes the model more applicable.