Yanguang Wang

Use of multicomponent seismic data for oil-water discrimination in fractured reservoirs

Geophysicists have devoted great efforts to the problem of determining fluid saturation from seismic measurements, with some notable successes. It is commonly believed that fluid information is to be found in the P-wave data, with shear waves being insensitive to fluid, and indeed almost all successful fluid-detection methodologies have been based on analysis of the P-wave.

Effects of oil‐water saturation on shear‐wave splitting in multicomponent seismic data

Understanding saturation changes is important in mature reservoirs. Here we analyze shear-wave splitting in a 3D3C onshore survey from Shengli Oilfield, China, where the thin sand-reservoir has been undergone production through water-flooding which altered the fluid composition and the pore-fluid pressure. Dividing the data into orthogonal azimuthal sectors and processing each sector separately reveals significant shear-wave splitting. The amount of shear-wave splitting can be correlated with the degree of water saturation. Furthermore, the slow shear-wave component shows amplitude dimming in water-flooded areas, whereas the zone of original oil in place shows only weak shear-wave splitting. Rock physics modeling based on the evolution of microcracked rocks and anisotropic fluid substitution incorporating both saturation and pressure changes confirm the observations. The saturation changes have little effect on the P and the fast shear-wave as confirmed by core analysis in the laboratory. However, the substitution of water for oil changes the fluid viscosity that has a strong effect on the slow (quasi) shear-wave. These observations reveal the potential of using shear-wave splitting for oil-water discrimination.

Joint frequency expanding method of crosswell seismic data and 3D seismic data

Crosswell seismic data and 3D seismic data are seismic response of different frequency band from the same geologic target. Crosswell seismic data possesses very high resolution in comparing with 3D seismic data for its higher main frequency and broader frequency band. However crosswell seismic data only exist between source well and receiver well, while 3D seismic data has excellent spatial distribution. It is possible to integrate different types of data and get more reliable underground information (Lines et al., 1988; Hu et al.,2007; Heinche et al., 2006). Here we put forward joint frequency expanding (JFE) method of crosswell seismic data and 3D seismic data. We expand 3D seismic data frequency band according to crosswell seismic data, and improve the resolution ability of 3D seismic data. First we use 3D seismic data and crosswell data to build 3D seismic reflect coefficient model, which possesses high resolution, and is consistent with 3D seismic data in structure. Second we use this reflect coefficient model as constraining condition, and joint inversion algorithm is used to get inverted reflect coefficients from 3D seismic data. Finally according to time-frequency analysis of 3D seismic data, we choose an appropriate high resolution wavelet to convolve with the inverted reflect coefficients, and produces high resolution 3D seismic data. Here we design a processing flow and applied it to Ken 71 data of ShengLi oil field. With the help of crosswell seismic data, 3D seismic data resolution is improved, main frequency is increased from 35Hz to 75Hz, and frequency band is also widened by 30Hz.

High frequency restoration of surface seismic data based on system identification

It is difficult to characterize subtle stratigraphic details accurately by surface seismic data with poor vertical resolution.A new method to restore high frequencies within the seismic bandwidth by utilizing velocity logging data has been proposed in this paper.On the assumption that seismic waves attenuate linearly in formations,a theoretical model is derived firstly to link surface seismic data and velocity logging data,and then the absorption system response is evaluated based on system identification technology,which can be used to compensate the attenuated high frequencies within the surface seismic bandwidth.The results of high frequency restoration for the forward modelling data and the actual surface seismic data show that the new method can enhance the vertical resolution of the surface seismic data significantly,which will advance the dominant frequency by 10Hz and 20Hz,widen the frequency band about 10Hz,while the principal features of the original surface seismic data still hold.