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Reservoir properties, such as pore types and wettability, are essential for shale gas reservoir evaluation. However, advanced nuclear magnetic resonance (NMR), which has been routinely used in petrophysical characterization of reservoirs, is barely used to estimate these properties in shale gas reservoirs. In this study, several sets of specially designed NMR measurements, together with total organic carbon (TOC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and contact angle tests, are used to study the pore types and wettability of Longmaxi shale gas reservoir. Results show that the NMR transversal relaxation time (T 2 ) spectrum can be used to characterize pore types and wettability of gas shale. Three identified T 2 spectral peaks (0.01−0.4 ms, 0.4−15 ms, and >15 ms) separately correspond to organic pores, inorganic pores, and microfractures, which is consistent with the results of FE-SEM. The T 2 spectra in as-received and water/ oil-imbibition states qualitatively prove that the microwettabilities of organic pores, inorganic pores, and microfractures are oilwet, water-wet, and mixed-wet, respectively. In addition, a novel wettability index is defined to reflect the microwettability of pores quantitatively. The dominant minerals and TOC jointly affect the pore wettability index; they show good correlations with the wettability index of inorganic and organic pores, whereas there is no obvious correlation with the wettability index of microfracture. In contact angle measurements, water and oil droplets show different behaviors on the surface of shale specimens, which qualitatively indicates that the macrowettability of Longmaxi gas shale is mixed-wet (both water-wet and oil-wet) and more prone to be oil-wet. After analysis of the theory of characterizing macrowettability by NMR, a new NMR-based model is proposed to characterize the macrowettability quantitatively. In summary, this study proposes novel methods and models to characterize the pore types and wettability, expanding the use of NMR in shale gas reservoirs.

There has been substantial development in computer codes for three-dimensional linear hydroelasticity, but to the authors’ knowledge, there are no problems of sufficient complexity put forth in the open literature to serve as appropriate benchmark problems for a floating structure. We present in this paper detailed descriptions of two such problems for three-dimensional hydroelastic computer codes. The first structure is a rectangular, box-shaped “barge” with dimensions 100 m×10 m×2 m. The second is a Wigley hull with dimensions 100 m×10 m×4.5 m. In both cases, the deformational response is primarily global. Detailed descriptions of each structure, the finite element structural shell models, and the hydrodynamic fluid models, based on the constant panel Green’s function method, are provided. Fine meshes are used to minimize discretization errors. Detailed results, including dry natural periods and modes, wet natural periods, and wave-induced displacements and stresses, are presented. The detail is sufficient for others to use the problems as benchmarks for computer codes.

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