Ordovician Carbonate Reservoir Prediction In The Ordos Basin

The Ordos Basin is the second largest sedimentary basin in China. The Ordovician carbonate reservoir generally has low porosity and permeability. These features of reservoir make the basin reservoir more subtle, which increases the technical difficulty of the exploration and development of the oil and gas on one hand, and on the other hand provides a good condition for long-term preservation of the oil and gas. It is very important to conduct a prediction of cave reservoir, fractured-vuggy reservoir and dolomite intercrystal reservoir of Ordovician in this area by comprehensive utilization of seismic data, logging data and drilling data.This area has complex geological structure, deeply buried carbonate reservoirs with low signal to noise ratio of seismic data in most areas. Carboniferous-Permian developed a large set of coal-bearing strata,missing Silurian and Devonian strata. Therefore, this paper combines the progressive impedance inversion with the S transform which has high energy fidelity, reliability and time-frequency resolution. Using the spectral decomposition techniques based on S transform, the post-stack seismic data are divided into different frequency scales. The low frequency seismic data reflect the large set of thick strata and the high frequency seismic data fully reveal the geological targets. Thus in the process of progressive impedance inversion, we first perform the inversion of low-frequency seismic data to obtain a low frequency impedance. Then the low frequency inversion results will be served as initial background constraint condition for the inversion high-frequency seismic data. At last, the progressive impedance inversion gets an inversion impedance data with both low and high frequency information, which is credible and stable.Combining core, logging, geological data and seismic data organically, we can analyze the impact of the mineral composition of rocks, porosity, pore fluid, the type of reservoir space and the aspect ratio of pore on the compressional wave, shear modulus, bulk modulus and Poisson’s ratio. As we all know that the pre-stack seismic data is rich in amplitude and travel-time information, in this paper, first we calculate the pseudo-elastic impedance curve at the well location according to lithological parameters of logging data and estimate shear wave velocity, then obtain the data volume of elastic impedance on the gathers with different angles, respectively and expand the progressive inversion to the pre-stack inversion. Therefore, we can conduct the high-resolution pre-stack progressive elastic impedance inversion.