Thermodynamic and Structural Characterization of Bulk Organic Matter in Chinese Silurian Shale: Experimental and Molecular Modeling Studies

Abstract

Silurian marine shale in Sichuan Basin is the most significant target zone for shale gas resources in China. In this work, a combined experimental and molecular simulation study was conducted to characterize the thermodynamic and structural properties of the organic matter in Silurian shale. Organic geochemistry experiments and Fourier transform infrared (FTIR) spectroscopy were performed to provide structural parameters for the main skeleton of the organic matter. A realistic molecular model of the organic matter under typical reservoir conditions was generated by molecular dynamics simulations based on the experimental results and documented analytic data. The thermodynamic and structural properties of the organic matter model were discussed in detail. Clear correlations are found among geochemistry properties and structural parameters of organic matter, independent of organic matter type and maturity. Aromatic units in the organic matter are highly condensed, and the interunit linkages are mainly short methylene groups. Ether groups are the dominant oxygenated compounds, while aromatic sulfur is the main form of organic sulfur. Reasonable consistencies are found on results of compositions of the organic matter fractions and physical density between simulated and available experimental data. The isothermal compressibility and thermal expansion coefficient correspond to the general range of a liquid. In addition to micropores, the organic matter contains a large amount of ultramicropores, which contribute a lot to the high porosity and specific surface area. The porous network is highly connected with few dead pores. Interestingly, the introduction of bitumen fractions has little effect on the spacing of polyaromatic units, but it aggravates the relative slippage of polyaromatic units. Also, separation of lighter compounds is observed in the structure. The carbon dioxide molecules are closer to the oxygenated groups, while the nitrogen molecules and methane molecules are closer to the sulfur functional groups and nitrogen functional groups. This proposed organic matter model can serve as a starting point for further theoretical investigations on gas adsorption and transport mechanisms, representative of the organic matter in Silurian shale at molecular scale.

The heat and mass transfer characteristics of superheated steam in horizontal wells with toe-point injection technique

“…In this section, type curves of SHS flow in IT and annuli are obtained and discussed in detail (Huang et al 2017(Huang et al , 2018a(Huang et al , 2018bFeng et al 2018;Sun et al 2017k, 2017l, 2018bZhang et al 2017aZhang et al , 2017bChen et al 2015Chen et al , 2016Chen et al , 2017. The injection pressure, temperature and mass flow rate at the heel point are 4.231 MPa, 566.6 K and 3 kg/s, respectively.…”

Molecular Structure of Kerogen in the Longmaxi Shale: Insights from Solid State NMR, FT‐IR, XRD and HRTEM

“…Several kerogen structural models have been built based on the qualitative or semiquantitative information provided by these methods (Requejo et al, 1992;Orendt et al, 2013;Craddock et al, 2017;Hackley et al, 2017;Longbottom et al, 2017;Stock et al, 2017). In addition, these 3D kerogen models have been used in methane adsorption and micropore structure analysis (Huang et al, 2017). However, the orientation and ordering degree of the aromatic layers, regarded as important spatial position information on the kerogen structure, has been ignored in most of the existing 3D kerogen models (Vandenbroucke and Largeau, 2007;Bousige et al, 2016;Huang et al, 2017).…”

“…In addition, these 3D kerogen models have been used in methane adsorption and micropore structure analysis (Huang et al, 2017). However, the orientation and ordering degree of the aromatic layers, regarded as important spatial position information on the kerogen structure, has been ignored in most of the existing 3D kerogen models (Vandenbroucke and Largeau, 2007;Bousige et al, 2016;Huang et al, 2017). Some studies have been performed on the structural alignment of coal (Mathews and Sharma, 2012;Romero-Sarmiento et al, 2014).…”

“…The nanoscale organic pores, which contribute to the largest part of the total pore volume, are the main storage space for shale gas (Wang Min et al, 2016). Meanwhile, it is well documented that some nanoscale organic pores (<2 nm) are formed within the three-dimensional (3D) molecular structure, and their pore structure parameters are controlled by the molecular composition and spatial structure of the organic matter (Bousige et al, 2016;Huang et al, 2017;Vasileiadis et al, 2017;Liu et al, 2018a). Therefore, the evaluation of gas storage and transport is strengthened by a robust understanding of the molecular structure of the organic matter.…”

Effect analysis of non-condensable gases on superheated steam flow in vertical single-tubing steam injection pipes based on the real gas equation of state and the transient heat transfer model in formation

“…In order to study the effect of injection temperature, various injection temperatures (590, 610 and 630 K) are tested based on no change in values of injection pressure and mass flow rate (Chen et al 2016(Chen et al , 2017Zhang et al 2017a, b;Sun et al 2017k, l, 2018bFeng et al 2018;Huang et al 2017Huang et al , 2018a. Besides, various values of mass content of non-condensing gases are added for comparison.…”