Yuchun Gao

With the depletion of conventional oil and gas resources, global attention has shifted to deep unconventional reserves. Carbonate reservoirs account for a substantial portion of worldwide hydrocarbon reserves. However, their heterogeneous pore systems comprising pores, cracks, and vugs pose significant challenges for parameter prediction. Deep carbonate reservoirs exhibit complex pore structures, pronounced heterogeneity, and ambiguous seismic responses. To address these, we integrate the microscopic Gurevich squirt flow model with the mesoscopic Biot-Rayleigh theory, yielding a multi-scale elastic rock physics framework. This framework quantifies interrelations among microcracks, porosity, and P-wave dispersion. It also incorporates effects of fluid viscosity, temperature, and pressure on seismic wave attributes. Using the Voigt-Reuss-Hill average, differential effective medium theory, and Batzle-Wang equations, we construct a multi-scale elastic rock physics template for the Shunbei area, centered on P-to-S-wave velocity ratio and P-wave impedance. By combining this framework with seismic data, the template enables prediction of reservoir porosity and crack porosity. Results demonstrate that the template-based method effectively delineates high-quality reservoirs. Predictions align well with well-test data from three wells, validating the approach.

Cutoff walls are used to reinforce embankments to prevent instability induced by reservoir seepage during water level fluctuations. This paper analyzes the stability enhancement provided by cutoff walls using the framework of limit analysis upper-bound method combined with a rotational log-spiral failure mechanism. Verification on unreinforced slopes shows that there is a high degree of consistency between the proposed upper bound results and existing analytical and numerical solutions. It was shown that the slope has a higher safety factor as the stabilizing effect of the cut-off wall strengthens. In addition, the critical sliding surface tended to be shallower with an increase in the external water level coupled with a decrease in the internal water level. Due to combined stabilization from soil self-weight and hydrostatic pressure, the stabilizing effect of the cutoff wall is not always necessary under all water level conditions; only when the wall is positioned within a critical normalized distance from the crest could the reinforcing effect of the cutoff wall be fully exerted.