Sensitivity Analysis of Petrophysical Parameters for Estimating Hydrate Saturation in the Shenhu Area
Acoustic and electrical methods are commonly used to evaluate hydrate saturation based on the P-wave velocity and resistivity, respectively. In this paper, petrophysical parameters, which are directly related to the presence of hydrates, are used to evaluate hydrate saturation. First, five petrophysical parameters sensitive to hydrate saturation are analyzed using the equivalent medium rock physical model (MBGL), logging intersection plots and petrophysical parameter inversion. Then, the simulated annealing global optimization method is used to estimate the hydrate saturation profile in the Shenhu area. The petrophysical parameters Vp, λρ and λμ, which are associated with the rock modulus (both the elastic modulus and shear modulus), are highly sensitive to hydrate saturation, with an estimated saturation range of 0.1-0.44. This range is highly consistent with that based on the original well diameter curves. However, the parameters Vs and μρ, which are only related to the shear modulus of the rock, yield high hydrate saturation estimates of 0.22-0.43 and exhibit some deviations from real data. Due to its sensitivity, Poisson's ratio (σ) is least desirable for hydrate evaluation among the studied parameters. The sensitivity of hydrate saturation depends on the petrophysical model used in studies of the physical properties of hydrate and analyses of hydrate storage.
Keywordsnatural gas hydrate saturation sensitive parameters petrophysical properties
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The study is supported by the National key research and development plan (2017YFC0307401), The study is supported by the Fund of Acoustics Science and Technology Laboratory (GK2050260214, GK2050260217, GK2050260218, KY10500180084, KY10500190031), National Natural Science Foundation of China (Nos.41304096, 41876053), the Fundamental Research Funds for the Central Universities (HEUCFJ180503, 201762019), the National Science and Technology Major Project of China (2016ZX05024-001-002).
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