The Application Of Seismic Logging Inversion Method In The Carbonate Reservoir Prediction

Salt Paleozoic of Caspian Basin is developing carbonate in shallow continental shelf, biogenic reef, and clastic reservoir. This reservoir is thick, widespread and has good reservoir characteristics. Caspian Basin is composed with sediments formed by the deep water phase "rich in organic matter", the basin went through the eastern margin uplifting, Hercynian orogeny, sea level declining, the later thick evaporite forming and salt tectonic moving, forming many small structures.Carbonate reservoir in ZhaNan area, for strong anistrope and complex reservoir distribution. The research ideas of this paper is: based on taking full advantage of previous research on carbonate reservoirs, taking the use of existing logging and seismic data analysis results, combined with diverse seismic logging inversion methods for predicting fine reservoir in current oil and gas exploration and compare the methods, the optimized inversion method suited to the area to predict the reservoir. In this study, the principle of each method, pivotal technology and application of conditions was studied in detail. the understanding as following:①Recursive inversion. The main principle of this method is using the reflection coefficient calculated by Taylor formula, and we establish the recurrence relation between wave impedance and the reflection coefficient for solving the problem step by step. The advantage of this method is that the wells impact factor is small, the inversion result can completely keep seismic reflection characteristics, there are no multiple results. The disadvantage is without using difference impedance values near the well trace and of the well’s to compute iterate inversion, can not get the absolute speed and impedance of the stratum. The result can not be used for quantitative calculation of reservoir parameters; the result is sensitive to noise in the record, limited by the seismic frequency band, and resolution is low, can not be adapt to the needs of thin explanation.②Recurrence inversion. The key is estimating reflection coefficient from the seismic recording, getting the best impedance information matching the drilled wells. In recurrence inversion, logging data is mostly played the role of calibration and quality controlling, which is also known as direct inversion and logging controlling seismic inversion. The advantage of the method is changing the wave solution from "underdetermined" into determined, and can get the inversion results near the well section mostly coincide with the well point. There is limitation: this method completely ignores the error of logging and seismic noise.③Constrained logging inversion. It is the method that forecast reservoir laterally based model, using seismic data constrained by well logging to inverse the target reservoir. The best advantage is the use high-frequency and low-frequency components of log data to recruit limited frequency bandwidth of seismic, with the known geological information and well logging data as constraints, by high-resolution stratigraphic inversion of impedance data for reservoir to provide a more detailed description of a reliable basis. Disadvantages are: in the inversion calculation, the impedance parameters (binding ratio) are free to changing, then the impedance parameters can not be accurately selected.