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Zhou D.-T.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | Li Z.-P.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

The studies on stress, strain and pore pressure of mudstone during heating are significant in many fields, such as heave oil recovery, nuclear waste storage and civil engineering. The literature investigation indicates that rare related works have been done in this area and ongoing studies still stay in infancy all over the world. To our knowledge, few experiments and models have been revealed in domestic research activities. While some thermo-elasto-plastic constitutive models are successfully created by introducing temperature effect into the modified clay-based Cambridge model. Here, a thermo-elasto-plastic model for mudstone is proposed, which is capable to simulate change of stress, strain and pore pressure under in-situ boundary conditions. Furthermore, inner bed mudstone data of Xinjiang's heavy oil field are applied in this model. Results of pore pressure and axial strain are obtained, and they agree with those of foreign experiments. By using the function for temperature field during steam chamber expansion of SAGD, constitutive failure of mudstone with different saturations is forecast. The results can effectively solve the problem that the inner bed mudstone hinders the steam chamber expansion. ©, 2015, Chinese Society of Civil Engineering. All right reserved. Source


Guo W.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | Guo W.,China University of Geosciences | Yao Y.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | Yao Y.,China University of Geosciences | And 5 more authors.
Oil and Gas Geology | Year: 2016

This study compared measurement results of total pore volume and pore size distribution of 6 coal samples with different coal ranks by using the Nuclear Magnetic Resonance Cryoporometry (NMRC) and low-temperature nitrogen adsorption BJH method. Meanwhile, the possibility and feasibility of applying NMRC to analysis of coal pore size distribution were evaluated for the first time. Results show that the total pore volume measured by NMRC is significantly larger than that of BJH method for the same coal sample. This is mainly caused by two factors. Firstly, in comparison with the BJH method, the NMRC can measure more closed pores. Secondly, the BJH model itself has some limitations in calculating the pore volumes of most micropores (<10 nm) and some meso-and macro-pores. Measurement results of coal samples with different coal ranks indicate that the total pore volume measured by NMRC shows a trend of decrease followed by an increase with increasing coal rank. This trend is consistent with the trend of the change of coal porosity with increasing coal rank. In contrast, the total pore volume measured by BJH does not match the trend of the change of coal porosity with increasing coal rank, due to the existence of outlier values in the measurement results of BJH method. Compared with the conventional methods, the NMRC has advantages in quantifying coal total porosity. Moreover, the results of NMRC are less influenced by some artificial factors. Thus, NMRC is a new method that can be applied to the measurement of pore structure of unconventional reservoirs. © 2016, Editorial Office of Oil and Gas Geology. All right reserved. Source


Wu J.,China University of Geosciences | Wu J.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | Wu J.,Key Laboratory of Shale Gas Exploration and Evaluation | Liu D.,China University of Geosciences | And 3 more authors.
Oil and Gas Geology | Year: 2014

To better understand the development characteristic of nanopores and its geological controlling factors, we collected 11 shale samples from the Taiyuan, Shanxi, and Yanchang formations in the Weibei, southeastern Ordos Basin, and performed low-temperature nitrogen adsorption, Argon-ion milled and field emission scanning electron microscopy (FE-SEM), vitrinite reflectivity (Ro) and maceral composition, total organic carbon (TOC) content and X-ray diffraction (XRD) analyses. The selected shale samples are in the transition period from low mature to mature, and are quite different in TOC. The nanopores in the shales are dominated by pores within the size of 2~50 nm, which account for 63.5% of the total pore volume. The BET specific surface area is commonly higher than 10 m2/g, indicating a favorable condition for methane adsorption. The pore types are mainly of narrow-slit pores and ink-bottle shaped pores. The dominant mineral compositions are different from area to area: clay minerals being dominated in the Hancheng area, while brittle minerals being dominated in the Tongchuan area. Clay mineral content is positively correlated with the total content of nanopores smaller than 2 nm and that within 2-50 nm, while the brittle mineral content is positively correlated with the content of nanopores larger than 50 nm. This means that the difference in mineral types is the main control factor on the development of nanopores. Moreover, Ro and TOC also have some influences on the development of nanopores. The higher the Ro is, the higher content of large nanopores is, but the lower content of medium to small nanopores is. In addition, the higher the TOC, the higher content of medium to small nanopores is. Source


Zhang H.,China University of Geosciences | Zhang H.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | Wang X.,China University of Geosciences | Wang X.,Beijing Key Laboratory of Unconventional Natural Gas Geology Evaluation and Development Engineering | And 2 more authors.
Mathematical Problems in Engineering | Year: 2015

This paper presents a new method to give an analytical solution in Laplace domain directly that is used to describe pressure transient behavior of partially penetrating hydraulic fractures in a box-shaped reservoir with closed boundaries. The basic building block of the method is to solve diffusivity equation with the integration of Dirac function over the distance that is presented for the first time. Different from the traditional method of using the source solution and Green's function presented by Gringarten and Ramey, this paper uses Laplace transform and Fourier transform to solve the diffusivity equation and the analytical solution obtained is accurate and simple. The effects of parameters including fracture height, fracture length, the position of the fracture, and reservoir width on the pressure and pressure derivative are fully investigated. The advantage of the analytical solution is easy to incorporate storage coefficient and skin factor. It can also reduce the amount of computation and compute efficiently and quickly. © 2015 He Zhang et al. Source

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