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Pore structure is the key element of tight sandstone reservoirs, which restricts the accumulate and flow of oil and gas in reservoirs. The pore structure is one of the key and difficult point of unconventional oil and gas exploration and development. In this paper, ten dense core samples from the Upper Triassic Yanchang Group 7 section in the Heshui area of the Ordos Basin are selected to carry out experiments, including high-pressure mercury pressure and X-diffraction. Fractal theory is used to analyze the characteristics of pore throats, then the relationship between fractal dimension and reservoir physical properties, pore structure and mineral content is analyzed. The results show that according to the mercury pressure curve and pore structure, the reservoir is divided into categories Ⅰ, Ⅱ and Ⅲ, its reservoir performance and seepage capacity decrease in turn, and the microheterogeneity is enhanced. Different types of reservoirs have different fractal characteristics: according to the inflection points of fractal curves 0.05 and 0.02 μm. The pore size of class Ⅰ reservoirs is divided into large pores (> 50 nm) and medium pores (50-6 nm) by combining the actual situation with the standard of pore size division proposed by IUPAC. According to the inflection point, the reservoirs of classes Ⅱ and Ⅲ can be divided into medium pores a (50-20 nm) and mesoporous B (20-6 nm). The average fractal dimension increased, which was 2.619 3, 2.745 4 and 2.852 6, respectively, and the heterogeneity gradually increased. The main permeability is contributed by fewer large pores, and the fractal dimension mainly reflects the heterogeneity of pore size. The fractal dimension is related to some minerals. Mineral composition and content are the internal factors that determine the fractal dimension and then affect the quality and pore structure of reservoirs.

With the rapid development of unconventional oil and gas resources, the demand for corresponding evaluation methods is increasing. At present, the evaluation methods for unconventional oil and gas resources are divided into analogy, statistical and genetic method. While constantly innovating evaluation methods, how to improve conventional methods and apply them to unconventional resource evaluation is also a focus and difficulty in current research. Taking a well as an unit and the EUR of the well as the unit's oil or gas reserves, a Pareto distribution model was established, and a program was compiled according to the principle of random sampling and skew sampling to analyze the sensitivity of number N, shape parameter and exploration coefficient E to the model. This method was applied to the shale oil resource evaluation in the X230 well block in Heshui area of Ordos Basin. Results show that the number of discoveries affects the size and dispersion of the parameters for oilfield distribution. The distribution model tends to be stable when the number is more than 300. Exploration coefficient has little influence on the sensitivity of distribution model, which is the limitation of taking EUR as evaluation unit. According to the variation of number N with shape parameter β, the number corresponding to cut-off point can be determined, that is, the sum of EUR of all wells is the recoverable resource of the area, which is 6.72×106 t. The result is consistent with the evaluation of oil and gas resource abundance. This method can provide guidance for unconventional oil and gas resources evaluation.

Pore structure restricts the reservoir capacity and flow capacity of oil and gas in the reservoir, which is the key factor of studying tight sandstone reservoir, and also the key and difficult problem of current research. Taking the Chang 7 tight reservoir of Upper Triassic Yanchang Formation in Heshui area of Ordos Basin as an example, the relationship between pore structure and movable fluid parameters was studied by combining high-pressure mercury injection and nuclear magnetic resonance (NMR) analysis techniques. The main results are as follows: ① when using the conventional method and linear least square method to convert the NMR T2 spectrum into pore radius, the pore structure can be divided into two parts, The correlation coefficient is (0.87-0.98)/0.92. The inflection point of the mercury injection curve is calculated by fractal theory, and the corresponding T2 is converted. The T2 spectrum is converted by segments. After the conversion, the curve has a high degree of overlap, and the number of phase relations is (0.97-0.99)/0.98. ② By analyzing the influencing factors of fluid mobility, it is found that there is a direct relationship between rock physical properties, in which porosity is more suitable to characterize the size of reservoir space, the correlation is 0.9, and the correlation with movable fluid saturation is better; The characteristic parameters of pore structure have a good correlation with the parameters of movable fluid, and the tight pore structure restricts the mobility of fluid. The proportion of dead pores is related to SMFS φ The negative correlation coefficients of MFS were 0.5371 and 0.3775, respectively φ MFS has little effect, but it has no effect φ MFS is more suitable to characterize the micro pore structure.

Cold seep and hydrothermal vent system have unique function in mass circulation of the earth, and have been explored by in situ detection technologies in past decades. A brief review on the development and the newest applications of in situ laser spectroscopy for deep sea research is presented here. The laser Raman spectroscopy and laser induced breakdown spectroscopy, with the advantages exactly meeting the requirement of the in situ detection, are emphatically introduced in this paper. The prospect of the in situ laser spectroscopy for the possible application in the deep sea is also discussed in this paper, aiming to provide a reference for the future development of spectroscopy.