Search for an alternative, cheap and environmental friendly EOR method has resulted in the development and subsequent field implementation of Smart Water Injection (SWI) and CO2 injection (COI). Though miscible COI has multi-fold advantages, carbonated water injection (CWI) may surpass COI in terms of volume requirement and efficiency. This research work is intended to investigate the advantages of combined application of SWI & CWI in terms of reduced residual saturations in oil wet carbonate formation. In order to measure the recovery efficiency, core flooding experiments are conducted with SWI as tertiary recovery following sea water as secondary recovery mode. This is followed by quaternary recovery using carbonated smart water (CSWI), i.e. smart water saturated with CO2. Three high potential smart water compositions are screened and the best one is chosen for the recovery studies. Produced water samples are analyzed using ICP-MS. The higher recovery efficiency of CSWI are analyzed in support of the NMR porosity distribution, interfacial tension and zeta-potential studies. The underlying physical processes and the pore-scale mechanisms of fluid-fluid and fluid-solid interactions during SWI-CWI are explained in terms of surface potential, electrical double layer, oil swelling factor, droplet coalescence, wettability alteration and flow diversion due to fluid redistribution within the pore network. Core flooding results showed that tertiary recovery with SWI resulted in 4.8 - 9.5% recovery, whereas the quaternary recovery with CSWI resulted in 5.7 % to 13.6% additional oil. From this study it is established that CSWI could be a promising EOR technique among the latest EOR methods. CSWI has an advantage over COI due to the fact that it exists as a dissolved gas instead of free phase. It reduces the requirement for high pressure injection system, the problems of gravity segregation and poor sweep efficiency. A hybrid of CWI with SWI can make it an effective EOR solution with significant cost advantage, higher oil recovery in addition to the environmental benefits of CO2 sequestration.
Search for an alternative, cheap and environmental friendly EOR method has resulted in the development and subsequent field implementation of Smart Water Injection (SWI) and CO2 injection (COI). Though miscible COI has multi-fold advantages, carbonated water injection (CWI) may surpass COI in terms of volume requirement and efficiency. This research work is focused on finding the benefits of combination of SWI & CWI in terms of reduced residual saturations in oil wet carbonate formation. In order to measure the recovery efficiency, core flooding experiments are conducted with SWI as a tertiary recovery following sea water secondary recovery. This is followed by quaternary recovery using smart water saturated with CO2 (CSWI). Three high potential smart water compositions are screened and the best one is chosen for oil recovery studies. Effluent samples collected at pre-defined pore volume injection intervals are analyzed in ppm level using ICP-MS. The analysis is supported by NMR porosity distribution studies, interfacial tension and zeta-potential studies. Core flooding results showed that tertiary recovery with SWI resulted in 4.8 - 9.5% recovery, whereas the quaternary recovery with CSWI resulted in 5.7 % to 13.6% additional oil. The underlying physical processes and the pore-scale mechanisms of fluid-fluid and fluid-solid interactions during SWI-CWI are explained in terms of surface potential, electrical double layer, oil swelling factor, droplet coalescence, wettability alteration and flow diversion due to fluid redistribution within the pore network. From this study it is established that CSWI could be a novel and promising EOR technique among the latest EOR methods. CSWI has an advantage over COI due to the fact that it exists as a dissolved gas instead of free phase. It eliminates the requirement for high pressure system, the problems of gravity segregation and poor sweep efficiency. Combination of CWI with SWI can make it an effective EOR solution with significant cost advantage, higher oil recovery in addition to the environmental benefits of CO2 sequestration.
In the oil and gas industry, Enhanced Oil Recovery (EOR) plays a major role to meet the global requirement for energy. Many types of EOR are being applied depending on the formations, fluid types, and the condition of the field. One of the latest and promising EOR techniques is application of ion-engineered water, also known as low salinity or smart water flooding. This EOR technique has been studied by researchers for different types of rocks. The mechanisms behind ion-engineered water flooding have not been confirmed yet, but there are many proposed mechanisms. Most of the authors believe that the main mechanism behind smart water flooding is the wettability alteration. However, other proposed mechanisms are interfacial tension (IFT) reduction between oil and injected brine, rock dissolution, and electrical double layer expansion. Theoretically, all the mechanisms have an effect on the oil recovery. There are some evidences of success of smart water injection on the field scale. Chemical reactions that happen with injection of smart water are different in sandstone and carbonate reservoirs. It is important to understand how these mechanisms work. In this review paper, the possible mechanisms behind smart water injection into the carbonate reservoir with brief history are discussed.
Carbonated water has proven advantages over conventional CO2 injection in terms of arresting free CO2 mobility, low-pressure injection, lower volume requirement, and higher efficiency. The term “engineered water” is designated to selective ion-spiked injection water with the advantage of the ion-exchange reactions with the rock minerals and releasing trapped oil. This article investigated the synergic effect of dissolved CO2 and engineered water for oil recovery and understanding inner mechanisms. Recovery efficiencies were evaluated through coreflood studies, which revealed that the hybrid water could recover 6–10% more oil than engineered water and about 3% more than carbonated water. HP-HT pendant-drop studies show the insignificance of IFT reduction. Wettability change from oil wet to near-water wet is attributed as a significant factor. The dissolution of Ca2+ and Mg2+ and deposition of SO42− observed in coreflooding may have a significant contribution to oil recovery. Pore enlargement evidenced in NMR-PSD and NMR-ICP results support this claim. The study confirmed that the EWI-CWI hybrid technique could be a promising EOR method, eliminating the requirement for high-pressure injection, the problems of gravity segregation, and the early breakthrough of CO2. It can also be an effective EOR solution, providing a significant cost advantage and higher oil recovery in addition to the environmental benefits of CO2 sequestration.
Discovery of new oil being in declining trend and demand being on the rise, EOR technologies has to play a bigger role in the future to meet the energy demand and economics. This paper presents a comprehensive review of EOR technologies related to alkaline flooding and its hybrids. Alkaline flooding is one of the chemical enhanced oil recovery techniques in which high pH alkaline chemicals are injected to the reservoir for recovering the residual oil. It is among the oldest EOR techniques and its history started way back in the early 20 th century. The history of alkaline flooding, mechanisms by which it recovers oil, different process variations, the effectiveness and costs of different alkalis, problems associated with alkaline flooding and its application in carbonates are briefly reviewed in this paper. This paper also focuses on the reviews of the application of various hybrid floods developed along with alkali and their advantages, limitations both in clastic and carbonate reservoirs. The technical solutions to some of these challenges will be discussed.
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