Study On Carbonate Reservoir Prediction Of Dengying Formation In Sichuan Based On 3D Seismic Data

Carbonate reservoir is the most productive reservoir,which provides more than half of oil and gas resources which is consumed.Carbonate reservoirs of Dengying Formation in a certain area of Sichuan are rich in oil and gas resources,but their development degree is low.The difficulty of exploration and development in this area lies in the strong reservoir heterogeneity and the low accuracy of conventional reservoir prediction methods.Due to karstification,the reflection wave coaxial in the upper fourth of the Dengying Formation is disordered,and small-scale fractures is widely distributed in most areas.The resolution of conventional fracture prediction methods is too low to accurately depict the location of fracture development.In view of the difficulties of exploration and development in this area,this paper makes a study from the following three aspects.(1)Aiming at the problem that the reservoir development degree in the study area varies greatly in vertical direction and the reservoir heterogeneity is strong,this paper proposes a method to delineate the favorable position of reservoir development in vertical direction based on horizon constraints.Firstly,the vertical development characteristics of reservoirs in different seismic facies zones are found through well-seismic calibration,and then the bottom interface of upper segment of Deng4 is reinterpreted from the perspective of reservoir prediction,which lays a foundation for subsequent reservoir prediction by geophysical methods.(2)In carbonate reservoir prediction,conventional amplitude attributes indirectly reflect reservoir development location by describing the amplitude of "bright spot" reflection related to karstification.Frequency attenuation gradient is a property that reflects gas-bearing property of reservoir by high frequency attenuation of seismic wave,thus describing reservoir location.The accuracy of reservoir prediction results in this area is low(the coincidence rate with actual logging data is less than 70%).In view of the great difference of reservoir lateral development in this area and the difficulty of reservoir prediction based on conventional seismic attributes,this paper improves the conventional method of wavelet decomposition and reconstruction in time domain.First,seismic signals are decomposed into three-parameter wavelets of different shapes,and then the waveforms related to reservoirs are selected to be reconstructed,so as to predict the lateral development position of reservoirs and predict the conclusion.The coincidence rate between the results and the actual logging data is 80%.(3)Aiming at the problems of cluttered seismic reflection wave,low signal-to-noise ratio,poor application effect of conventional prediction methods in the study area and difficulty in fracture prediction,this paper proposes an improved coherence cube technology,which improves the anti-noise ability of the technology by processing the original seismic data with three-dimensional envelope denoising and filtering the coherence results.This method can clearly depict the location of fracture development,distinguish the degree of fracture development,and completely coincide with the interpretation of logging data.The application results of the above methods in the study area show that the new horizon is helpful to extract seismic attributes and find high-quality reservoirs.The improved wavelet decomposition and reconstruction technology can accurately describe the lateral development position of reservoir.The improved coherence cube technique can accurately predict the development location of large-scale and small-scale fractures.