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Oil shale is an unconventional energy source with abundant reserves. However, the global oil shale resources have not been fully exploited. In-situ oil shale extraction technology based on electric heating has gradually become a research focus in this field. In this study, the construction of a numerical simulation model for the in-situ extraction of oil shale by electric heating and the results of the numerical simulation study are summarized. By summarizing the research progress and current status of numerical simulation of electrically heated in-situ oil shale extraction, the core issues, main challenges, progress made, and bottlenecks to be solved in the current numerical simulation research are analyzed. [ABSTRACT FROM AUTHOR]

The pore structure can affect the storage and flow properties of rock, which is an important research content in the study of unconventional tight reservoirs. This research hopes to clarify the reservoir characteristics and fluid seepage mechanism of the Chang 9 reservoir in the Wucangpu block and provide technical support for the development of horizontal wells with staged fracturing in this block. In this paper, the microscopic pore structure characteristics and producibility of the reservoir in the study area are analyzed in detail by means of constant-rate mercury intrusion and nuclear magnetic resonance. The research results show that the reservoir with permeability less than 0.076 mD is mainly composed of microthroat, the reservoir with permeability of 0.208-0.633 mD has a larger proportion of microthin throat, and the reservoir with permeability of 2.722-3.998 mD has a larger proportion of fine-middle throats. The results show that the oil/gas in the rock sample reservoirs with permeability greater than 1.0 mD is easy to produce. [ABSTRACT FROM AUTHOR]

Spontaneous imbibition is an important mechanism in naturally fractured reservoirs. In our previous studies on the effect of imbibition efficiency of ultra-low permeability reservoirs, we mostly focused on the relationship between macroscopic core recovery rate and influential factors. Additionally, we also mainly focused on the factors that control the final imbibition recovery for ultra-low permeability reservoirs. Through a large number of experiments, it was found that the factors affecting imbibition are different in separate stages. However, the relative importance of those factors in different imbibition stages was hardly studied. In this work, we tested six key factors, i.e., the core length, RQI, salinity, interfacial characteristics, initial oil saturation, and oil viscosity, in natural sandstone samples from Chang 6 in the Zichang area. Based on experimental results, we divided the imbibition process into three stages (i.e., the early stage, the middle stage, and the late stage) to quantify the effects of the controlling factors. The results show that the relative importance of the controlling factors is changing during the imbibition process. The weight of importance is obtained for those factors at each stage. In addition, a comparative model is established for the dual-porosity media from Chang 6 formation. The results show that the increase of the rock size can extend the imbibition period for the early and middle stages. Moreover, the weight of importance for the initial oil saturation, interfacial characteristics, and salinity are also analyzed in three imbibition stages. This study provides theoretical support to guide water injection in ultra-low-permeability reservoirs and to understand the formation of energy supplements and oil recovery during the imbibition process. [ABSTRACT FROM AUTHOR]

Oil shale, as an unconventional energy source, has attracted much attention in countries worldwide. The traditional way of extracting oil shale from the open pit is not only costly but also polluting to the environment. Sufficient understanding of the relationship between subsurface fractures and temperature fields is important for the extraction of oil shale and is of great significance for the actual in-situ extraction of oil shale. The study of fracture initiation and expansion in oil shale formations is based on the effect of fractures on convective heating efficiency in oil shale in situ conversion technology. In view of the objective situation that hydraulic fracturing can enhance the rate of the permeability and heating efficiency of oil shale formations, and hence the oil yield, the effect of single fractures with different fracture heights (2 mm, 4 mm, 8 mm) on the temperature field of oil shale; and the effect of multiple fractures (two, three and four fractures) on the temperature field of oil shale are investigated under convective heating methods. [ABSTRACT FROM AUTHOR]