Implementing Seismic Colored Inversion to Enhance Reservoir Property Estimation in Frontier Exploration Areas: A Case Study in Central Saudi Arabia, Unayzah Reservoir

Abstract Seismic Inversion methods have been in use in the industry for over 46 years. The earliest form of seismic inversion simply transformed seismic data to P-impedance, which is the product of density and P-wave velocity. The result was then used to predict reservoir properties such as lithology and porosity to better characterize reservoirs. This, however, proofed to be difficult as the P-impedance velocity also responds to the inseparable effect of reservoir fluids, lithology and porosity. The introduction of S-Impedance, which is less susceptible to the effects of fluid and lithology, made the results less ambiguous. Modern inversion uses algorithms that account for wavelet amplitude and phase spectra, which improved its utility in various reservoirs. There are several types of Inversion algorithms used in the industry. Sparse Spike inversion aims at explaining the seismic reflectivity with the minimum set of layers. It can generate both relative and absolute inversion. In this type of inversion the contribution of the logs (low impedance) and the seismic (high impedance) is clearly defined. Model-based inversion is another class of inversion technique. This class of algorithms tries to achieve resolution beyond the seismic band by using impedance logs in the model. It also utilizes interpretations like faults and horizons to produce better result, which means extra work is need. There is also stochastic inversion algorithms which produce high resolution, non-unique inversion cubes and thus may take more time. However, they enable statistical analyses of these solutions. Other forms of inversion include colored inversion and inversion by trace integration (Pendral, 2001). The exploration of frontier areas characterized by complex geology and sparse well control requires fast, iterative, intuitive, and accurate methods to estimate reservoir properties. Traditional full-band seismic inversion is time consuming and typically requires the expertise of an inversion specialist. Also the quality of the inversion results islimited by the lack of well control, which is required to construct an accurate background (low frequency) impedance model. The seismic colored inversion method has proven to be a novel method that provides both speed and accuracy in delineating reservoir properties across vast frontier areas with few well controls.