The full waveform inversion (FWI) method utilizes the kinematic and dynamic information of prestack seismic data to rebuild underground velocity structure.It has the potential of revealing detailed structure and lithology characteristics under complex geological background.FWI can be carried out in the either frequency or time domain. Frequency-domain FWI has the advantages of high computation efficiency and data selection flexibility over its time-domain counterpart.Recent advances in frequency-domain FWI including waveform modeling methods,frequency selection strategies,object function configuration styles,source wavelet processing methods,and gradient precondition methods make it attractive for realistic problems.The multiple local minimal nature of the object function js one of the major obstacles to good reflection waveform inversion results.The frequency-domain damped wavefield inversion method fills the gap between the Laplace-domain and frequency-domain FWI methods.The combination of the three methods can mitigate the strong nonlinearity of the waveform inversion problem.
Unconventional reservoirs, such as tight gas sand, coal‐bed methane and shale gas reservoirs will play an important role in stable domestic nature gas production in China during the next decade. The complex geological conditions and drilling risks are the major difficulties to the successful development of these resources. Integration of multi‐discipline analysis including geophysics, rock physics and geology will help to reduce the costs. We present a multistage, target oriented prestack full waveform inversion procedure to estimate tight gas sand in Xujiahe Formation in the northeast Sichuan basin, taking account of prior information from well log data and some basic geological knowledge. Spatial distributions of tight gas sand estimated from the final inverted elastic models are consistent with current well interpretation and gas production test results. The study results indicate that the multi‐stage prestack full waveform inversion strategy is practical for tight gas sand detection in this region.
Structural interpretation is the fundamental of reservoir prediction, and enhancing the precision of interpretation is an effective method to improve the effect of prediction. Various techniques are used to achieve high precision of structural interpretation, including fine horizon calibration, enhancing the quality of seismic data, increasing the grid density, horizons tracking and fault interpretation on the knowledge of geology. The paper discusses the method of improving the precision of structural interpretation in complex small fault‐block zones of Qintong depression.
Full waveform inversion (FWI) has the power of estimating velocity models from prestack seismic data in arbitrary complex regions. We present a frequency domain layer‐stripping FWI method utilizing information from damped reflection waveform. The observed data is weighted in time domain and Fourier transformed into frequency domain, while the forward and inverse problems are formulated directly in frequency domain. We have assessed this layer‐stripping FWI method with Marmousi model and typical short‐offset surface geometry. Numeric results showed this damped reflection waveform inversion algorithm can speed up convergence even in several iterations, especially for the shallow portion of the model.
The prospecting work in Qintong depression, North Jiangsu basin, a typical area of complex fault‐block in the east of China, aims to find fault‐block traps and structure‐lithology traps, for which high standard of precision of structure mapping is required. The general geological background of this area, such as fractured structure, well developed faults, igneous rock intrusion, greatly influence the precision of seismic velocity, and increase the error of structure‐mapping. Based on prestack time migrated gather, the method we proposed can give an accurate velocity model through a special velocity analysis workflow constrained by wells and horizons, eliminating the affection caused by undesirable geological factors. According to prospecting objects and mapping requirements, adequate space velocity‐variant aperture is determined; finally the whole space velocity model is obtained, objectively reproducing the subsurface structural pattern. With our method, the average velocity is highly correlated with T0 maps, and the structure maps are consistent with the results of well drilling.
In this paper we present a seismic inversion method for inverting reservoir crack density from P-wave AVOA data. We discuss in detail the relationship between the elastic constants, anisotropic parameters and crack characteristic parameters of a fractured medium, derive a primary equation for inverting the crack density, and then study a two-step algorithm with reducing inversion parameters. We demonstrate the feasibility, efficiency and robustness of the method by using numerical tests.
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