Study On High Resolution Reservoir Prediction Base On Well Bore Geophysics And Surface Seismic Data

At present, in the most of big oil & gas fields in this world, especially the oil fields in the east part of China, the newly found oil & gas in place are predominantly from subtle reservoirs, which are very hard and costly to be developed. The existing problems are mainly due to the shortage of effective methods and technologies to predict and describe this kind of reservoir, especially the poor resolution being far from what is required. Thus it is very urgent and necessary to study and develop a high resolution prediction method to meet the demand of exploration and exploitation at present stage.In this paper a high resolution reservoir prediction method is presented based on well bore geophysics and surface seismic data, which is quite different from the traditional ways of relying only on surface seismic survey, well log constrained seismic inversion with sparsely and irregularly distributed wells at a plane and attributes to predict a reservoir. In this new method, either a single technique of the well bore geophysics or the combination of well bore geophysics with surface seismic survey are all very challenging and pioneering. In fact, they are the difficult and hotspot researching targets facing most of the scientific research institutes, oil companies and geophysical service companies in this world.After studying thoroughly each single technique of the well bore geophysical methods including VSP, cross well seismic survey etc. this paper focused on the integrated application of well bore geophysics with surface seismic survey for the purpose of increasing the ability to recognize a reservoir in both horizontal and vertical direction so that the reservoir could be predicted with high resolution. Case studies showed very good result. This means the method is of great importance to subtle reservoir and it can be popularized and well applied in the future. The most important achievement and technical innovation of this paper include the following. (1) The first DMO formulas of VSP are derived, and secondly acquired Q-value from data of zero offset are respectively compensated to VSP and surface seismic data to find finally the differential correction factor between surface seismic traces at the entrance of the well bore and the VSPLOG within a time span window and then to be extended to those traces near the well bore. By using the above technical plan, the high frequency part of seismic data is compensated effectively and good result is got in practical seismic data processing.(2) A compound technical scheme of inversion and its realization was presented by using cross well seismic impedance, well log impedance and VSP frequency expanded seismic data. Through research on VSP inversion method, cross well seismic inversion method and the compound inversion by using cross well seismic data, well log data and 3D seismic data, some key problems related to high resolution reservoir inversion were discussed including fine seismic and geological demarcation, fine inversion wavelet estimation and 3D constrained model building. The emphasis was laid on the application of the stochastic inversion based on maximum a posteriori probability (MAP) estimation, the Metropolis and the Heat Bath inversion algorithm of the simulated anneal stochastic inversion method.(3) According to the characters of cross well seismic survey and the need of reservoir prediction, a study of cross well seismic data interpretation in the depth domain was performed including fault interpretation on the basis of wave group correspondence or coherence, reservoir interpretation method on the basis of sedimentation pattern or recycle or frequency spectrum analysis or inversion or seismic attribute analysis.(4) Based on the elastic theory model of multiple lithofaces, systematically analyzing the regular relation between petrophysical and acoustic characters of rock. This paper discussed a bunch of impact factors affecting the acoustic properties of rock, such as the impact of porosity, shale content, saturation, pressure and temperature on the acoustic speed of rock, and also the relation between S wave and P wave. This study was used in the petrophysical analysis at F124 block and led to a reliable interpretation model including porosity model, permeability model and saturation model etc. (5) A set of high resolution and compound prediction methods of reservoir were created based on well bore geophysics and surface seismic survey and they had been applied to F124 block of some prospect with good result. The quality of seismic data were improved after utilizing VSP to expand its frequency spectrum, with effective frequency span from 10 to 50 Hz being upgraded to 10 to 60 Hz. The resolution and precision of inversion result and reservoir prediction were improved by integrating 3D seismic data which are processed and upgraded by VSP information to a higher resolution, cross well seismic impedance inversion, well log and other effective information from a lot of data. By compound interpretation and application of the above data, a new work was done to recognize the geometric shape and rock properties at F124 block. The least sand thickness described was 3m. By statistics from newly drilled wells, we can see the prediction result was greatly improved by using the above mentioned technologies.