Dynamic And Static Characterization Of Reservoirs Constrained By Time-lapse Seismic Prestack Inversion

Time-lapse seismic exploration is one of the most important means for accurately establishing underground geological model,enhancing oil and gas recovery and predicting remaining oil distribution in the middle and late stages of development of many old oilfields.The technology of reservoir detection based on time-lapse seismic realizes the transformation of reservoir from static description to dynamic characterization.Time-lapse seismic inversion is an important part of this technology.Therefore,how to obtain high-precision and high-resolution parameters from seismic data becomes a key factor in reservoir model construction.Based on inversion theory and time-lapse seismic data,here introduces some methods to obtain more accurate and stable inversion results,and constructs static and dynamic reservoir models with petrophysical means.Firstly,we have developed a model-based pre-stack waveform inversion with a generalized propagation matrix(GPM)scheme as forward operator,where a regularized function is minimized with the L-BFGS technique to determine a model update corresponding to an adaptively determined regularization weight in each iterative step.To avoid falling into local extrema in the process of solving the objective function,we introduce an optimal transport method into the objective function to improve its convexity and use L-curve method to acquire the optimal regularization weight adaptively.The model tests show that the proposed scheme performs better than the conventional method significantly both on convergence and on accuracy.Further,we apply the pre-stack inversion with the proposed inversion scheme to the well-logging data and real seismic data.The results demonstrate that the proposed inversion scheme is not only capable of obtaining an accurate description of subsurface properties,but also has good convergence and robustness.Then,based on the modified Hertz-Mindlin rock physical model and pre-stack inversion theory,a static model driven by rock physical model is proposed.The sensitivity of three basic reservoir parameters,effective pressure,rock porosity and water saturation,to seismic data is obtained by sensitivity parameter analysis,and three parameters are obtained by seismic data inversion.The prediction accuracy of porosity and effective pressure can be guaranteed to a certain extent,while the prediction results of water saturation parameters are easily influenced by other factors.By deriving Fr Chet derivative,the inversion strategy of reservoir parameters using pre-stack seismic data is realized.Moreover,we propose a frequency-dependent pre-stack inversion workflow to extract the wave-induced fluid flow(WIFF)effect from seismic data.The proposed approach consists of three essential parts,comprising spectral decomposition,Q-compensated pre-stack inversion,and frequency-dependent pre-stack inversion.Firstly,L1 norm constraint inverse spectral decomposition(ISD)is exploited to provide time-frequency amplitude and phase spectra with high resolution and reliable accuracy.Then,constant-Q compensated pre-stack inversion is used to generate relatively precise P-and S-wave velocities,density and Fr�chet derivative for the subsequent dispersion inversion.Finally,frequency-divided seismic data(resulting from part1)and the estimated parameters and Fr�chet derivative(derived from part 2)are used to invert the P-wave velocity dispersion.A comparison between the inversion results and band-limited rock physics analysis results shows that the proposed method can provide a quantitative inversion of the velocity dispersion to some extent.The proposed strategy provides a possibility for quantifying dispersion and further estimating gas saturation.Finally,a method of dynamic characterization of model parameters based on time-lapse seismic difference inversion is proposed.Its principle can be divided into two parts: instant-lapse seismic difference inversion and time-lapse seismic synergistic inversion.In time-lapse seismic difference inversion,a modified approximation is proposed to make the forward operator simulate the real wave field as accurately as possible,and the improved approximation is applied to time-lapse seismic difference inversion.In the cooperative inversion of time-lapse seismic data,we get the relationship between the model parameters and the model parameters through the channel integration algorithm.Then,the relationship is used as the constraint condition of the cooperative inversion,and the joint inversion of time-lapse seismic data is carried out by combining multi-period time-lapse seismic data.