The carbon dioxide flooding of oil reservoirs represents one of the most-proven tertiary oil recovery practices. However, there are significant challenges associated with applying CO₂ flooding in certain onshore or offshore fields and applications. The common challenges include a limited supply of CO₂, transportation, capital cost investment, and corrosion. For offshore flooding, the critical challenge could be more related to extreme remote and significant project cost increase. In this work, we investigated delivering CO₂ indirectly to the subsurface formation by injecting the concentrated solution of ammonium carbamate (AC) as CO₂ generated species. Ammonium carbamate, a highly water soluble solid (40 wt %) and commercially available, can be dissolved in aqueous solution and injected to the reservoir where it decomposes at reservoir condition, thus releasing products of CO₂ and ammonia. The produced CO₂ results in lowering oil viscosity and oil swelling. Increase of ammonia concentration also lead to sand wettability reversal due to elevated alkalinity. Tertiary oil recovery performance of ammonium carbamate solution was evaluated by conducting multiple sand packs and core flooding test at various pressure and temperature conditions. Dodecane and several dead crude oils were used as oil phase. Injected AC concentrations tested were ranging from 5 to 35 wt %, with operational pressure, pressure (P) ranging from atmospheric to 4000 psi, and the preset temperature ranging from 96 to 133 °C. The average tertiary recovery observed from all the tests was found to be 29%. Results of laboratory experiments clearly demonstrated the potentials of this novel formulation for tertiary oil recovery. Mainly, it requires minimal capital investment up-front in comparison to CO₂ flooding and largely eliminates the occurrence of gravity segregation and reduces adverse fingering behaviors because there is no presence of a free-CO₂ phase involved. This endeavor serves as a successful proof of concept for the potential applications in tertiary oil recovery for both onshore and offshore fields.

中文翻译：

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开发用于提高采油量的原位CO ₂生成配方

油藏中的二氧化碳驱是最成熟的三次采油实践之一。然而，在某些陆上或海上领域和应用中施加CO ₂驱油存在很大的挑战。共同的挑战包括有限的CO ₂供应，运输，资本成本投资和腐蚀。对于海上洪水而言，严峻的挑战可能与极端偏远和项目成本显着增加有关。在这项工作中，我们研究了通过注入氨基甲酸铵（AC）的浓溶液作为CO ₂来将CO ₂间接输送到地下地层的方法。产生的物种。氨基甲酸铵是一种高度水溶性的固体（40 wt％），可商购获得，可以溶解在水溶液中并注入储层，在储层条件下分解，从而释放出CO ₂和氨的产物。产生的CO ₂导致油粘度降低和油溶胀。氨浓度的增加还由于碱度升高而导致沙子润湿性反转。通过在不同的压力和温度条件下进行多个沙包和岩心驱油试验，评价了氨基甲酸铵溶液的三次采油性能。十二烷和几种死原油用作油相。在操作压力，压力（P）的温度范围为大气压至4000 psi，预设温度范围为96至133°C。从所有测试中观察到的平均三次回收率被发现为29％。实验室实验结果清楚地表明了这种新型配方在三次采油中的潜力。主要是，与CO ₂驱油相比，它需要最少的前期资本投资，并且由于不存在游离的CO ₂相，因此大大消除了重力偏析的发生并减少了不利的指弹行为。这项努力为陆上和海上油田三次采油的潜在应用提供了成功的概念证明。