Zhishui Liu

The theory and application of DEM-Gassmann rock physics model for complex carbonate reservoirs

The storage spaces of carbonate reservoirs in the Tarim Basin are dominated by secondary pore porosity such as dissolution caves, holes, and cracks (Song et al., 2001). Research has shown that pore shapes can significantly influence the velocities of elastic waves (Eshelby, 1957; Kuster and Toksoz, 1974; Xu and White, 1995; Yan et al., 2002; Sun et al., 2004). Empirical VP-VS relationships such as Castagnas (1985) mudrock line, Hans relations (1986), and Greenberg-Castagnas (1992) relationship that ignore the effect of pore geometry are not applicable to carbonates (Xu and White, 1995; Wang et al., 2009). Cheng and Toksoz (1979) imaged various pore space structures using SEM, and proposed a pore aspect ratio spectrum that can be used to explain velocity prediction. Han (2004) measured velocities of 52 different carbonate rocks, indicating that caves influence seismic velocities due to high rigidity while micropores or cracks significantly decrease velocities of rocks due to the low rigidity. Regarding ...

The differential Kuster–Toksöz rock physics model for predicting S-wave velocity

The Kuster–Toksoz (KT) model is a classical rock physics model concerning the influence of pore geometry on elastic wave velocities. However, this model is limited to a dilute concentration of pores, which means the porosity cannot be too high. In order to overcome this limitation, this paper transforms the KT model into a new differential Kuster–Toksoz (DKT) model. In other words, we propose a process in which porosity with certain geometries increases step by step from zero up to its final value. The simulation of the new model notably shows that it is superior to the classical KT model and the differential effective medium model since it takes multiple–porosity and higher porosity rocks into consideration. Furthermore, by combining the DKT model, the Gassmann equation and the Voigt–Reuss–Hill average equation, a S-wave velocity prediction procedure is proposed under the constraint of the P-wave velocity which is from the logging data. The new method is applied to both the measured data in laboratory and well data in logging. The results show that the predicted S-wave velocities match well with the measured ones, especially for data with high porosity. By comparing estimated S-wave velocity deduced from the new method and the KT model, the results demonstrate that the new method is effective for S-wave velocity prediction.

Quantitative inversion of carbonate secondary pore structure using rock physics model

Generally, carbonate secondary pore structure is very complex, such as, for the dissolution fractured and caved carbonate reservoir in Tarim Basin. The complex secondary pore structure can significantly influence seismic wave velocities, bringing great difficulties for the exploration and characterization of this type of reservoir. Therefore the determination of carbonate secondary pore structure (mainly pore shapes) is quite important. In this paper, the DEM-Gassmann velocity prediction model proposed by us formerly is inversely employed to invert the carbonate secondary pore types in the calibration of both Pand Swave velocities derived from logging data. The volume fraction of each pore type can be determined quantitatively. Through comparing with the results indicated in FMI and core data, the mismatching rate of the inversion results is quite low, proving the availability and reliability of this method for carbonate secondary pore structure inversion.