页岩油开采外文文献翻译.docx

1、页岩油开采外文文献翻译页岩油开采外文翻译中英文2019英文Improving oil recovery from shale oil reservoirs using cyclic cold carbon dioxide injection An experimental studyKhalid Elwegaa，Hossein Emadi, etcAbstractIn this study, effects of injecting gas temperature and pressure on oil recovery factor (RF) of shale oil reservoirs

2、were investigated by implementing cyclic cold carbon dioxide (CO2) injection on Eagle Ford Shale Oil core samples. Also, effects of injecting gas temperature on porosity, permeability, and brittleness indices of these core samples were assessed.An experimental setup was designed and built to impleme

3、nt CO2cyclic gas injection and thermal shock tests. Four Eagle Ford Shale outcrop core samples were used in this study. The saturated samples were heated to 180F and carbon dioxide at various combinations of pressure (1000 psi, 2000 psi, 3000 psi, and 4000 psi) and temperature (15F, 0F, 32F, and 74F

4、) was injected into them. Oil RF for each experiment was measured after five days of production period. Additionally, porosity, permeability and ultrasonic velocity of each core sample were measured both prior to and after conducting the experiment.The results indicate that injecting CO2at low tempe

5、rature results in higher oil recovery factor (up to 7%) than injecting carbon dioxide at ambient temperature. It was also observed that injecting cold CO2enhanced both porosities and permeabilities of the core samples. The porosities and the permeabilities of the core samples enhanced by up to 3.5%

6、and 8.8%, respectively. Also, a noticeable reduction (between 100ft/s and 400ft/s) in P-wave velocity was observed after injecting the cold gas into the core samples, which is an indication of creating induced fractures. The results also revealed that injecting the cold gas increased the brittleness

7、 indices of the core samples by up to 8. Hence, cyclic cold carbon dioxide injection could be potentially implemented in the shale oil fields to improve the efficiency of the current industry practice of cyclic gas injection technique.Keywords: Shale oil reservoirs, Cyclic gas injection, Carbon diox

8、ide, Oil recovery, Thermal shock1.IntroductionShale formations have ultra-low permeabilities and do not produce economically unless fracturing treatments are performed. Despite using current stimulation techniques, shale reservoirs only produce 57% of their initial oil in place. Therefore, researche

9、rs are still working on exploring new techniques to improve recovery factor (RF) in shale-oil reservoirs. Consequently, several Enhanced Oil Recovery (EOR) techniques have been studied to improve ultimate oil RF. One of the most promising techniques is cyclic gas injection “Huff and Puff”, which has

10、 been successfully implemented in both conventional and unconventional reservoirs using different gases (nitrogen and carbon dioxide).In this study, effects of temperature of injecting CO2on oil RF in shale oil formations was investigated. In this experimental study, CO2was injected into four core s

11、amples at different pressures and temperatures and oil RF at the end of each test was calculated.It is believed that rapidly injecting cold gas into hot formations creates cracks at the exposed surface area of the rock, which increases oil RF. This technique is called thermal shocking. Since thermal

12、 shock creates fractures at the rock surface, it is believed that porosity, permeability and rock mechanical properties of the rock samples will be altered too. So, porosity and permeability of the samples were measured before and after each injection test. Also, ultrasonic velocity measurement test

13、s were conducted to assess changes in dynamic youngs Moduli and Poissons ratios of the core samples.Since Eagle Ford is one of the largest unconventional resources in the U.S., core plugs from its outcrop were obtained and used in this study. Additionally, CO2was used in this experimental study beca

14、use of its successful implementations in EOR operations in the past decades.13reported that the following parameters may contribute to increase in oil RF using carbon dioxide; reduction of oil viscosity, miscibility effects, and internal solution gas drive.1.1.Cyclic gas injection methodCyclic Gas I

15、njection also known as huff-and-puff technique is an efficient EOR method in which a gas is injected into a reservoir either in miscible or immiscible condition (huff cycle). Then the well is shut-in for a “soak” period to allow the injected gas to interact with the formation oil and reach equilibri

16、um. At the end of the soaking period, the production is resumed through the same well (puff cycle).This method has been successfully implemented in shale oil fields.9reported that CO2greatly enhances the diffusion process, which improves hydrocarbon transport in tight matrixes (especially densely fr

17、actured shale-oil formations).Using CO2and shale cores from Mancos and Eagle Ford,4conducted a laboratory study to investigate effects of soaking period, soaking pressure and number of cycles on oil RF. The results showed that cyclic CO2injection is an effective method to improve oil RF from shale o

18、il reservoirs.9conducted an experimental work injecting high-pressure CO2into 21 core samples from Bakken shale formation to enhance the diffusion-dominated flow in the reservoir matrix. The results indicated that CO2is able to recover up to 99% of oil from middle Bakken formation and 68% from upper

19、 and lower Bakken formations. Another CO2huff-n-puff experimental study in a supercritical state was carried out using low permeability core samples. The results showed that the cyclic CO2injection in supercritical state can significantly improve the efficiency of oilfield development for low permea

20、bility reservoirs15. In contrast, formation damage could occur when CO2is injected into formations due to calcium carbonate precipitation and brine content. Several parameters affect the interaction between CO2and formation rock including pressure, temperature, brine composition and CO2injection rat

21、e. The reaction between CO2and formation rock could result in permeability reduction11.In addition to the experimental studies, CO2cyclic gas injection technique was successfully implemented in some oil fields. This method was successfully implemented on 240 wells in the Big Sinking Field of eastern

22、 Kentucky, USA. Using liquid CO2resulted in additional recovery of 180,000 barrels of oil from the field10. Another field implementation of CO2cyclic gas injection was carried out in Jiangsu oil field, China. The results demonstrated improvement in well productivity due to dissolution of CO2and near

23、 wellbore damage removal20.1.2.Low temperature gas injectionIn this technique, gas at a low temperature is injected into hot reservoirs. This process is called thermal shock technique, which leads to creating thermal stress on the rock. The thermal stress results in creating new fractures and/or ext

24、ending existing cracks yielding to higher oil RF. Using Eq. (1), thermal stress applied to a solid body due to temperature change is calculated.In the last few years, experimental works have been conducted to study thermal shock technique and its applications in the oil and gas industry. Using liqui

25、d nitrogen,2conducted cryogenic fracturing tests on concrete, tight sandstone, and Niobrara shale samples. The results showed that injecting liquid nitrogen not only enhances rocks permeabilities (especially shale samples), but also, has almost no formation damage potential.23conducted rock mechanic

26、al properties tests under cryogenic conditions (rock samples were subjected to liquid nitrogen). The results showed that shear and tensile strengths of the rock samples significantly decreased after being subjected to liquid nitrogen. Thermal shock caused by the cryogenic treatment could create new

27、microfractures and extend the existing ones.21conducted cryogenic fracturing experiments to investigate its effects on the permeabilities of eight-inch cubic synthetic rock samples (concrete). Eight tiny thermocouples were embedded in the samples to monitor changes in temperature during the test. Li

28、quid nitrogen was circulated into the samples through 6-in.-deep holes while the samples were subjected to triaxial compression. The results showed that the permeabilities of the affected area increased.3concluded that cryogenic fracturing is a stimulation technology, which deploys cryogenic fluids

29、to fracture unconventional oil and gas reservoirs.6conducted a non-isothermal compositional simulation study to examine effect of injecting low temperature CO2on oil RF in a high temperature reservoir. The results showed that injecting liquid CO2increases ultimate oil RF by 8.73% compared to supercr

30、itical CO2injection in isothermal mode (200F) after 24years of production.2.Experimental workIn this study, several experiments were conducted to investigate effect of temperature of injecting CO2on oil RF in shale oil reservoirs. Detailed description of porosity, permeability, ultrasonic velocity m

31、easurements and cyclic gas injection experiment are given in the following sections. Four Eagle Ford core plugs were used in this experimental study. These cores were cut parallel to the bedding planes and were all 1.5 in diameter and 3 in length.2.1.Porosity measurementA helium porosimeter was used

32、 to measure the effective porosities of the core samples. The porosities were measured both prior to and after conducting the injection tests.2.2.Permeability measurementNew Research England (NER) AutoLab 1500 (was used to measure permeabilities using complex transient method and helium.Fig.shows a jacketed core sample mounted between the low-permeability transducer and the bottom plug. The permeabilities of all core samples were measured before and after conducting CO2injection tests. The results were then used to study effect of the the