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With a more complex pore structure system compared with clastic rocks, carbonate rocks have not yet been well described by existing conventional rock physical models concerning the pore structure vagary as well as the influence on elastic rock properties. We start with a discussion and an analysis about carbonate rock pore structure utilizing rock slices. Then, given appropriate assumptions, we introduce a new approach to modeling carbonate rocks and construct a pore structure algorithm to identify pore structure mutation with a basis on the Gassmann equation and the Eshelby-Walsh ellipsoid inclusion crack theory. Finally, we compute a single well’s porosity using this new approach with full wave log data and make a comparison with the predicted result of traditional method and simultaneously invert for reservoir parameters. The study results reveal that the rock pore structure can signicantly influence the rocks’ elastic properties and the predicted porosity error of the new modeling approach is merely 0.74%. Therefore, the approach we introduce can effectively decrease the predicted error of reservoir parameters.

To fully extract and mine the multi-scale features of reservoirs and geologic structures in time/depth and space dimensions, a new 3D multi-scale volumetric curvature (MSVC) methodology is presented in this paper. We also propose a fast algorithm for computing 3D volumetric curvature. In comparison to conventional volumetric curvature attributes, its main improvements and key algorithms introduce multi-frequency components expansion in time-frequency domain and the corresponding multi-scale adaptive differential operator in the wavenumber domain, into the volumetric curvature calculation. This methodology can simultaneously depict seismic multi-scale features in both time and space. Additionally, we use data fusion of volumetric curvatures at various scales to take full advantage of the geologic features and anomalies extracted by curvature measurements at different scales. The 3D MSVC can highlight geologic anomalies and reduce noise at the same time. Thus, it improves the interpretation efficiency of curvature attributes analysis. The 3D MSVC is applied to both land and marine 3D seismic data. The results demonstrate that it can indicate the spatial distribution of reservoirs, detect faults and fracture zones, and identify their multi-scale properties.

Rock in the subsurface composed of rock matrix and pore fluid is a two-phase medium. So the effective elastic parameters of rock are influenced by rock matrix, pore structure and pore fluid. Therefore, in order to get the relationship between porosity and effective elastic parameters of rock, the influence of the other factors must be removed. Based on the basic theory of rock physics and test data, we propose the concept of equivalent volume and introduce the Eshelby ellipsoid inclusion fracture theory. With reasonable assumption, the Gassmann equation is applied to deduce and establish the equation between porosity and related factors including the compressibility of saturated rock (no drainage), the compressibility of rock matrix, pore aspect ratio describing pore shape and parameter m, and simulate properly pore structure in reef-flat reservoirs which are of strong heterogeneity. The test on real data proves that the formula between porosity and elastic parameters we build can be used to predict porosity of reef-flat reservoirs effectively.

In hydrocarbon reservoirs, seismic waveforms become complex and the correlation dimension becomes smaller. Seismic waves are signals with a definite frequency bandwidth and the waveform is affected by all the frequency components in the band. The results will not define the reservoir well if we calculate correlation dimension directly. In this paper, we present a method that integrates empirical mode decomposition (EMD) and correlation dimension. EMD is used to decompose the seismic waves and calculate the correlation dimension of every intrinsic mode function (IMF) component of the decomposed wave. Comparing the results with reservoirs identified by known wells, the most effective IMF is chosen and used to predict the reservoir. The method is applied in the Triassic Zhongyou group in the XX area of the Tahe oil field with quite good results.

Summary With a more complex pore system compared with clastic rocks, carbonate rocks have not yet been well described by the present conventional rock physics models concerning its vagary of pore geometry as well as the influence on elastic properties of rocks. To better understand the intrinsic effect on carbonate rocks’ properties, we propose a factor depicting the pore geometry of rocks based on conventional rock physics models in this paper. We start with a discussion and an analysis about the pore geometry of carbonate rocks. And then, we give introduction to a new approach of modeling carbonate rocks and construct a pore structure factor of carbonate rocks with a basis of the Gassmann equation and Eshelby-Walsh ellipsoid inclusion crack theory. Finally, we discuss the mutation relationship of pore structure factor with other elastic modulus parameters, analyze the pore structure factor with experiment data and logging data, and make a quantitative calculation of porosity. The results of theoretical study and case study reveal that the pore geometry of rocks can significantly influence the rocks’ elastic properties, and the approach we introduce can effectively decrease the predicted error of porosity and hence improves its prediction accuracy.