VI Annual International Conference and Exhibition - Galperin Readings 2006

In the report the effective method for reconstruction of thin layered structure of geological strata is suggested on the basis of dynamical inversion of low frequency surface seismic records and account of data of well acoustic logging. In result it is possible to reconstruct space structure and properties of separate layers in thin layered structure between wells on the scale less then wavelength.

Restoration of high and low frequencies is an important problem to be solved for VSP data in many applications such as prediction of acoustic impedance beneath the bottom of hole and extrapolation of log data away from the well. An iterative algorithm is proposed for estimation of full spectrum of VSP pulse seismogram. The method is based on an analytical extension of spectrum. The computing results for simulated and real VSP data are discussed. It is shown that the method is effective for high signal to noise ratio VSP data.

The paper presents results of surveying two complex geology prospects in the Perm Region by deploying polarization offset VSP method.

Method of increasing quality of CDP/LOG-VSP tie by stacking primary reflections of PP- and PS-waves from several shot points. The efficiency of this method was illustrated on synthetic and real data.

Despite of a large number of tasks successful solved by well seismic, we can see a situation when it is impossible to receive answers to the questions put by geologists – interpreters. This article describes the examples when insufficiently though-out and valid spread layout basically cannot provide the initial data guaranteeing decision of some problems. Particularly, influence on quality of initial data by such spread layout parameters as offset, span in borehole and manner of tools fastening (i.e. hold-down construction) in the well is shown.

Acoustic properties of geological section are the source for estimating of important reservoir characteristics such as lithology or porosity. The advantages of borehole seismic over surface seismic make VSP data attractive for calculation of high-resolution acoustic (AI) and shear elastic (SEI) impedance sections. On the other hand there are a number of factors affecting amplitude anomalies related to reflector acoustic properties variations. This study was performed to find the way of offset VSP data processing
preserving true amplitudes.

Adding static shifts to the number of unknowns in travel times inversion would not lead to the success, especially in processing of zero-offset vertical time-depth curves and also in the case of variation of the static shifts during the borehole measurements. Suggested alternative approach consists in using the subtractive vertical time-depth curves, obtained by calculating of time arrival differences for different waves recorded in the same receiver points. Reduced subtractive time-depth curves allow determining the layer model with higher assurance comparably with the one obtained for single time-depth curves. In addition, using the differences between time arrivals of the same wave from the same source to different receiver points is suggested. There through, influence
of static shifts on the determined seismic parameters in the limits of the accepted model is eliminated. Algorithms and computer programs developed by the authors are based on applying of optimization methods to the differential timedepth curves for waves of different types and classes. Efficiency of the programs was confirmed by the results of model and experimental studies.

The main feature of the offset VSP works, conducted in the Komarinaya area in West Siberia, consisted in using spatial system with 12 shot points, situated in different azimuths and offsets reaching about 1100 m from the wellhead. This allowed verifying the geometry of reflecting boundaries, to plot the structure maps using migrated depth sections and to make conclusions concerning the direction of subsequent drilling.

Additive Deconvolution is a method applied to seismic traces for obtaining first join times of signals having predefined shape. Unlike the classic deconvolution the method does not involve the computing of reverse filter operator. A seismic trace is therefore considered as a sum of weighted signals of predefined shape and noise. To obtain the coefficients of joining impulses are used the Fourier transformation and the least-squares method.

The functional potentialities of VSP, successfully applied to various tectonic areas of the Republic of Bashkortostan, are systematized in this Article. Ways of cooperation between OJSC “JSNC “Bashneft” and OJSC “Bashneftegeofizika”, used as an example, show high efficiency and prospectiveness of the new form of cooperation between oil-production companies and servicing geophysical organizations – VSP-support of deep drilling at various stages of geological exploration.