页岩油开采外文文献翻译Word下载.docx

1、F and carbon dioxide at various combinations of pressure （1000 psi, 2000 psi, 3000 psi, and 4000 psi） and temperature （15F, 0F, 32F, and 74F） was injected into them. Oil RF for each experiment was measured after five days of production period. Additionally, porosity, permeability and ultrasonic velo

2、city of each core sample were measured both prior to and after conducting the experiment.The results indicate that injecting CO2at low temperature results in higher oil recovery factor （up to 7%） than injecting carbon dioxide at ambient temperature. It was also observed that injecting cold CO2enhanc

3、ed both porosities and permeabilities of the core samples. The porosities and the permeabilities of the core samples enhanced by up to 3.5% 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 sa

4、mples, which is an indication of creating induced fractures. The results also revealed that injecting the cold gas increased the brittleness 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 eff

5、iciency of the current industry practice of cyclic gas injection technique.Keywords: Shale oil reservoirs, Cyclic gas injection, Carbon dioxide, Oil recovery, Thermal shock1.IntroductionShale formations have ultra-low permeabilities and do not produce economically unless fracturing treatments are pe

6、rformed. Despite using current stimulation techniques, shale reservoirs only produce 57% of their initial oil in place. Therefore, researchers are still working on exploring new techniques to improve recovery factor （RF） in shale-oil reservoirs. Consequently, several Enhanced Oil Recovery （EOR） tech

7、niques have been studied to improve ultimate oil RF. One of the most promising techniques is cyclic gas injection “Huff and Puff”, which has been successfully implemented in both conventional and unconventional reservoirs using different gases （nitrogen and carbon dioxide）.In this study, effects of

8、temperature of injecting CO2on oil RF in shale oil formations was investigated. In this experimental study, CO2was injected into four core samples 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 formati

9、ons creates cracks at the exposed surface area of the rock, which increases oil RF. This technique is called thermal shocking. Since thermal 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.

10、 So, porosity and permeability of the samples were measured before and after each injection test. Also, ultrasonic velocity measurement tests 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 resour

11、ces in the U.S., core plugs from its outcrop were obtained and used in this study. Additionally, CO2was used in this experimental study because of its successful implementations in EOR operations in the past decades.13reported that the following parameters may contribute to increase in oil RF using

12、carbon dioxide; reduction of oil viscosity, miscibility effects, and internal solution gas drive.1.1.Cyclic gas injection methodCyclic Gas Injection 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

13、 （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 equilibrium. 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 fi

14、elds.9reported that CO2greatly enhances the diffusion process, which improves hydrocarbon transport in tight matrixes （especially densely fractured shale-oil formations）.Using CO2and shale cores from Mancos and Eagle Ford,4conducted a laboratory study to investigate effects of soaking period, soakin

15、g pressure and number of cycles on oil RF. The results showed that cyclic CO2injection is an effective method to improve oil RF from shale oil reservoirs.conducted an experimental work injecting high-pressure CO2into 21 core samples from Bakken shale formation to enhance the diffusion-dominated flow

16、 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 and lower Bakken formations. Another CO2huff-n-puff experimental study in a supercritical state was carried out using low permeability core samples. The results

17、 showed that the cyclic CO2injection in supercritical state can significantly improve the efficiency of oilfield development for low permeability reservoirs15. In contrast, formation damage could occur when CO2is injected into formations due to calcium carbonate precipitation and brine content. Seve

18、ral parameters affect the interaction between CO2and formation rock including pressure, temperature, brine composition and CO2injection rate. The reaction between CO2and formation rock could result in permeability reduction11.In addition to the experimental studies, CO2cyclic gas injection technique

19、 was successfully implemented in some oil fields. This method was successfully implemented on 240 wells in the Big Sinking Field of eastern Kentucky, USA. Using liquid CO2resulted in additional recovery of 180,000 barrels of oil from the field10. Another field implementation of CO2cyclic gas injecti

20、on was carried out in Jiangsu oil field, China. The results demonstrated improvement in well productivity due to dissolution of CO2and near 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 t

21、hermal shock technique, which leads to creating thermal stress on the rock. The thermal stress results in creating new fractures and/or extending 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 y

22、ears, experimental works have been conducted to study thermal shock technique and its applications in the oil and gas industry. Using liquid nitrogen,2conducted cryogenic fracturing tests on concrete, tight sandstone, and Niobrara shale samples. The results showed that injecting liquid nitrogen not

23、only enhances rocks permeabilities （especially shale samples）, but also, has almost no formation damage potential.23conducted rock mechanical properties tests under cryogenic conditions （rock samples were subjected to liquid nitrogen）. The results showed that shear and tensile strengths of the rock

24、samples significantly decreased after being subjected to liquid nitrogen. Thermal shock caused by the cryogenic treatment could create new microfractures and extend the existing ones.21conducted cryogenic fracturing experiments to investigate its effects on the permeabilities of eight-inch cubic syn

25、thetic rock samples （concrete）. Eight tiny thermocouples were embedded in the samples to monitor changes in temperature during the test. Liquid nitrogen was circulated into the samples through 6-in.-deep holes while the samples were subjected to triaxial compression. The results showed that the perm

26、eabilities of the affected area increased.3concluded that cryogenic fracturing is a stimulation technology, which deploys cryogenic fluids to fracture unconventional oil and gas reservoirs.6conducted a non-isothermal compositional simulation study to examine effect of injecting low temperature CO2on

27、 oil RF in a high temperature reservoir. The results showed that injecting liquid CO2increases ultimate oil RF by 8.73% compared to supercritical CO2injection in isothermal mode （200F） after 24years of production.2.Experimental workIn this study, several experiments were conducted to investigate eff

28、ect of temperature of injecting CO2on oil RF in shale oil reservoirs. Detailed description of porosity, permeability, ultrasonic velocity measurements and cyclic gas injection experiment are given in the following sections. Four Eagle Ford core plugs were used in this experimental study. These cores

29、 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 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 me

30、asurementNew 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