Preventing channeling flows during enhanced oil recovery targeting heterogeneous or fracture type reservoirs and leakage flows from saline aquifers containing CO2 remains a challenge. This study evaluated the potential of in-situ gelation as a blocking agent in a heterogeneous reservoir using the reaction between aqueous solution of sodium metasilicate (Na2SiO3 9H2O; S _ MS) and dissolved carbon dioxide (CO2). Both Raman and scanning electron microscopy/energy dispersive X-ray (SEM-EDS) spectroscopy revealed that the gel was a sodium carbonate type (S _ C-gel). Physical characterization of the S _ C-gel including the gelation time, gel strength and stability, were investigated in respect of S _ MS concentration, temperature, salinity (NaCl), divalent ion concentration (calcium, Ca 2) as well as CO2 injection pressure. Gelation time after CO2 gas injection was around 1 to 24 h depending on temperature and pressure. Gel strength increased with higher S _ MS concentration (≤ 10 wt%) and CO2 gas pressure (≤ 5.5 MPa). Threshold pressure gradient (TPG) and gas permeability of the sandstone core filled with in-situ gel increased by 2.6 times and decreased about 1/10, respectively, compared with the water saturated core. These promising findings herein could be extended to CO2 sequestration.
There is a critical situation that a huge amount of greenhouse gases is emitted into the atmosphere from natural coal fires in underground coal seams and spontaneous combustions in coal piles in the world. To reduce the emissions of combustion gases, such as CO 2 , CH 4 , etc., some technical challenges and researches are required related to CO 2 flux measurements, developing an effective chemical water-solution extinguishes coal fires and inhibits spontaneous combustion, constructing a numerical simulation model to treat the aging effect in coal heating rate.In this article, firstly, the previous studies were reviewed to explain measurement results of CO 2 emission from coal fire/spontaneous combustion fields and the aging model used to simulate coal heating rate. Secondary, a trial development of some chemical solutions has been introduced to inhibit microscopic and macroscopic coal oxidations by forming a gel. Especially, sodium meta silicate solution showed a relatively good performance shifting the critical self-ignition temperature (CSIT) of a low rank coal to be 4 to 5℃ higher than that of water by forming gel with CO 2 gases in the air and combustion gases emitted from coals. The brooking effect in macro scale by forming gel is also expected to extinguish coal seam fires by reducing aperture width in fractures connecting to the atmosphere. A numerical simulation using ANSI FLUENT has showed an extinguishing fire process of an underground coal seam including a horizontal fracture that is connected inlet and outlet fractures being air paths for air and combustion gas, respectively.Finally, the the research challenges required for technical developments have been proposed to carry a project extinguishing the coal seam fires and spontaneous combustions of coal piles with reducing CO 2 emissions.
In this paper, the technical challenges in enhanced oil recovery using a sodium silicate solution as a multi-purpose chemical are introduced to enhance oil recovery by alkaline flooding and prevent channeling flows through high permeability layer/regime and geological storage of carbon dioxide (CO 2 ) . We have focused on the sodiummetasilicate-hydrates (Na 2 SiO 3 .9H 2 O; S -MS) from many types of chemicals. Firstly, oil properties with S -MS solution (pH12-13) are presented to carry out alkaline flooding based on measurement results of interfacial tension (IFT) , contact angle and emulsion formation with oil considering reservoir-water salinity. Secondary, in-situ gel formation using the reaction between S-MS solution and dissolved CO 2 is introduced as a blocking agent in high permeability owpasses in an oil reservoir with different permeability layers. Both of Raman and SEM -EDS spectroscopy revealed that the formed gel is a sodium carbonate type gel (SC -gel) . Physical characteristics of SC-gel were investigated in respect of S-MS concentration, temperature and CO 2 gas pressure. The blocking effect was evaluated by threshold pressure gradient and gas permeability by forming in-situ SC -gel in a sandstone core. Then the core ooding test using heterogeneous core consists from two sandstones cores with different permeabilities was carried out to nd improvements in oil recovery by alkaline ooding using S -MS solution and blocking effect by the in-situ gel formation with CO 2 gas injected. Furthermore, a new system (a kind of Carbon-dioxide capture, utilization and storage) using the S -MS solution is proposed for CO 2 capture, usage and geological storage into relatively shallow oil reservoirs or aquifers meet a safe and economical onshore CO 2 sequestration. Furthermore, it is also expected that the in-situ gel formation between S -MS solution and CO 2 gas emitted from res of peat layer or coal seam has a possibility to extinguish large scale res contributing global warming. Keywords:Enhanced oil recover y, Alkaline flooding, Blocking, CO 2 sequestration, Sodium silicate solution, Gel formation, Shallow aquifer, CCUS * 令和 2 年 10 月 28 日,石油技術協会令和 2 年度学術大会開発・生産 部門シンポジウム「石油増進回収(EOR)の未来-多様性と持続性, 実証ステージへの展開-」にて,講演題名「油層内原位置ゲル生成 技術を用いた EOR と CO 2 固定」で講演 This lecture was presented at 2020 JAPT Development and Production Technology Symposium entitled "The Future of Enhanced Oil Recovery(EOR)-Development to the demonstration stage of diversity and sustainable EOR techniques" held on Oct. 25-31, 2020.
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