Abstract
In order to reveal the shale oil production mechanism and production efficiency under the energy-depleted development mode, experiments on expulsion oil based on imbibition and elastic energy release under high temperature and pressure were carried out, and nuclear magnetic resonance on-line monitoring was used to observe the production characteristics of shale oil. The experimental results show that the imbibition-expulsion oil mainly occurs in the small-size pore-throat system. Under the condition of high temperature and pressure, the oil-expulsion efficiency is generally less than 2% affected by pore pressure, which is significantly different from the conventional imbibition experiment results. Although elastic-energy expulsion oil occurs in different sizes of pore-throat systems, the oil-expulsion efficiency in large size pore-throat systems is more sensitive to temperature. Overall, the total elastic-energy oil-expulsion efficiency is significantly positively correlated with reservoir physical properties, production differential pressure and temperature, and negatively correlated with crude oil viscosity. Comprehensively considering various geological factors affecting oil-expulsion efficiency, the shale oil production efficiency evaluation model under the energy-depleted development mode is constructed, and the movable oil porosity of shale oil development section in the study area is evaluated. The results show that there is a good positive correlation between movable oil porosity and oil production intensity. The movable oil porosity of dry layer is generally lower than 0.5% and that of poor oil layer is between 0.5% and 1.5%. When the movable oil porosity is between 1.5 and 2.5%, it can be determined as the type II oil layer, and for more than 2.5%, it is the type I oil layer. The single-well evaluation results show that the shale oil “sweet spots” of the Lucaogou Formation in Jimsar Sag are mainly distributed in P2l22−1∼ P2l22−3 and P2l12−1∼ P2l12−3, which is in good agreement with the current development status.
Highlights
China is rich in shale oil resources and has stepped from the stage of finding “sweet spot” to developing “sweet spot”
nuclear magnetic resonance (NMR) T2 spectrum show that the crude oil signal decreases gradually with the imbibition time in the low T2 area (Figure 3), which intuitively shows that the imbibition phenomenon mainly occurs in the small porethroat system
1) Imbibition-expulsion oil mainly occurs in the small-size pore-throat system and the oil-expulsion efficiency is negatively correlated with the reservoir physical properties
Summary
China is rich in shale oil resources and has stepped from the stage of finding “sweet spot” to developing “sweet spot”. The development of medium–high mature shale oil is feasible, but its economic benefits are restricted by factors such as oil price, construction cost, and single-well productivity, which is closely related to the resource abundance and crude oil mobility. Based on supercritical CO2 displacement method, Feng et al (2019) characterized the movable efficiency and movable lower limit of tight oil and clarified the relationship between movable oil rate and reservoir physical properties. This method represents the maximum amount of crude oil that can be recovered in tight reservoir by existing technologies, but it cannot be carried out on a large scale due to the production cost constraints. Digital cores were established to explore the seepage law of fluid in tiny spaces by many foreign scholars (Passey et al, 2010; Desbois et al, 2011; Iglauer et al, 2013; Hemes et al, 2015), but due to the strong heterogeneity of unconventional reservoirs, the digital core model is suffered from the problem of under-representation, so it is difficult to popularize and apply
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
