Estimating seismic impedance and elastic parameters in hydrocarbon-bearing reservoirs from acoustic logs

An equation was developed for estimating approximate and theoretical values of seismic impedance Z from acoustic logs, specifically in the absence of density data. This formula, which explicitly uses the effects of shale, matrix and fluid properties, describes pore-fluid effects in hydrocarbon-bearing reservoirs with an acceptable degree of accuracy. In the limit, when the pores are filled with low-density gas, this equation predicts unrealistically slow velocities (long transit times). Accordingly, better equations are routinely recommended for modeling fluid effects. on the equation, a suggested system for evaluating the fundamental elastic parameters, including Youngʹs modulus (E), shear modulus (μ) and bulk modulus (K) of any rock material, is also introduced. in advantages of the proposed approach are: (1) it is applicable for many shaly formations independently of the distribution of shales; (2) it allows the determination of seismic impedance and elastic parameters with a high degree of accuracy particularly in the absence of density information; and (3) it gives a quick-look interpretation of old wells, that suffer from an insufficiency of borehole data. Application of the equation is illustrated with field data in a shaly-sand formation of a Gulf of Suez example.