Amplitude preserved VSP reverse time migration for angle-domain CIGs extraction

An improved method of generating angle-domain common-image gathers（ADCIGs） by VSP reverse time migration（RTM） is introduced in this paper.The formula which is used to compute the receiver wavefield for VSP RTM is modified by adding an amplitude correction term in order to conveniently output amplitude-preserved ADCIGs.Compared with the surface seismic data,VSP data contains much richer wavefields.However,the direct and downgoing waves can bring about serious imaging artifacts in ADCIGs,especially the direct wave.The feasibility and validity of this method is demonstrated by both numerical and real VSP data from western China.Thus,the ADCIGs from this method can provide reliable basic data for VSP migration velocity analysis,VSP AVO/AVA analysis,and inversion.

True-amplitude wavefield separation using staggered-grid interpolation in the wavenumber domain

Wavefield separation of multicomponent seismic data to image subsurface structures can be realized in either the space domain or the wavenumber domain. However, as the particle velocity components used in the wavenumber-domain wavefield separation are not defined at the same grid point with the staggered-grid finite-difference method for elastic wavefield simulation, we propose the wavenumber-domain interpolation method to estimate the required values at the common grid points prior to the wavenumber-domain true-amplitude wavefield separation. Moreover, numerical experiments show that the wavenumber-domain interpolation method has high interpolation accuracy and the trueamplitude wavefield separation method shows good amplitude preservation. The application of the proposed methodology to elastic reverse-time migration can obtain good amplitudepreserved images even in the case of some velocity error.

Preserved amplitude migration based on the one way wave equation in the angle domain

Traditional pre-stack depth migration can only provide subsurface structural information. However, simple structure information is insufficient for petroleum exploration which also needs amplitude information proportional to reflection coefficients. In recent years, pre-stack depth migration algorithms which preserve amplitudes and based on the one- way wave equation have been developed. Using the method in the shot domain requires a deconvolution imaging condition which produces some instability in areas with complicated structure and dramatic lateral variation in velocity. Depth migration with preserved amplitude based on the angle domain can overcome the instability of the one-way wave migration imaging condition with preserved amplitude. It can also offer provide velocity analysis in the angle domain of common imaging point gathers. In this paper, based on the foundation of the one-way wave continuation operator with preserved amplitude, we realized the preserved amplitude prestack depth migration in the angle domain. Models and real data validate the accuracy of the method.

Analysis of Information of Oil-bearing Reservoir Using Seismic Attributes Technique——A Case Study of HD4 Oilfield, Tarim Basin

The theoretical and practical analysis of reservoir thickness and oil-bearing information of thin reservoirs is performed by using seismic attributes and forward modelling. The results show that thin reservoir can be recognized using seismic attributes technique when its thickness is less than 1/4 of wavelength. Through analyzing the influence of tuning effect, the relationship between thin layer thickness and tuning amplitude is well revealed. A precise structure interpretation is conducted using relative amplitude preserved high-resolution seismic data. By taking the geologic condition and well data into account, the distribution of oil and gas of HD4 oilfield is analyzed and predicted. based on seismic attributes. The result is helpful to promote the exploration and development in this oilfield.

AVO inversion based on common shot migration

Conventional AVO inversion utilizes the trace amplitudes of CMP gathers. There are three main factors affecting the accuracy of the inversion. First, CMP gathers are based on the hypothesis of horizontal layers but most real layers are not horizontal. Greater layer dip results in a greater difference between the observed CMP gathers and their real location. Second, conventional processing flows such as NMO, DMO, and deconvolution will distort amplitudes. Third, the formulation of reflection coefficient is related to incidence angles and it is difficult to get the relationship between amplitude and incidence angle. Wave equation prestack depth migration has the ability of imaging complex media and steeply dipping layers. It can reduce the errors of conventional processing and move amplitudes back to their real location. With true amplitude migration, common angle gathers abstraction, and AVO inversion, we suggest a method of AVO inversion from common shot gathers in order to reduce the effect of the above factors and improve the accuracy of AVO inversion.