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摘要
There are a large number of isolated pores in organic matter (OM) of shale reservoirs, and the isolated pores contain the adsorbed gas and free gas. Experiments showed that when there is a concentration difference between the adsorbed gas on nanopores surface and dissolved gas in OM, gas exchange occurs between the pore surface and OM. The difference of gas concentration among the connected pores, the OM and the isolated pores in the production process leads to the gas transport between the OM and isolated pores, which has a significant impact on shale gas predicted reserves and production. In this study, we consider the effects of the gas transport and desorption in isolated pores. With the low pressure gradient, the adsorbed gas can desorbs from the pore surface of high pressure regions, and then transport to the low pressure regions and adsorbs on the pore surface in isolated pores. The adsorbed gas can desorb into OM by the concentration difference, and then diffuses as dissolved gas in OM. The apparent permeability model coupled with viscous flow, slip flow, Knudsen diffusion, surface diffusion and gas desorption is adopted in the connected pores and isolated pores. Based on the above understanding, a model that considers the gas transport in the connected pores, the OM and the isolated pores is established. And the effects of the isolated porosity, degrees of isolated pores dispersion and dissolved gas diffusion coefficient are analyzed. The results shown in this work are strongly affected by the diffusion coefficient of dissolved gas, and when the diffusion coefficient is small, the contribution of the gas production in isolated pores to the cumulative gas production becomes minimal. Hence, with the large diffusion coefficient, when the gas transport is not considered in isolated pores, the existence of isolated pores hinders the diffusion of dissolved gas and result in a significant reduction of cumulative dissolved gas production in OM. And the contribution of the gas in isolated pores gas to the cumulative production cannot be neglected, the cumulative production of shale gas increases with the increase of isolated porosity. The larger the dispersion degree of isolated pores is, the greater the cumulative gas production is. The diffusion coefficient of dissolved gas has a positive effect on the production rate of the gas in isolated pores. The influence of gas transport in isolated pores on the diffusion of dissolved gas and the seepage law of shale gas reservoirs cannot be neglected.
- 出版日期2018-9
- 单位中国石油大学（华东）
