Hybrid EOR Technology: Carbonated Water-Smart Water Flood Improved Recovery in Oil Wet Carbonate Formation: Part-II

Abstract

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.

Mechanistic study of the carbonated smart water in carbonate reservoirs

“…10,11 CLSW takes advantage of the high CO 2 solubility in the low salinity water (salting-in phenomenon), which ensures a high mass transfer of CO 2 from the CW to the oil, based on 3-7 times higher affinity of CO 2 to be dissolved in oil than in water. [3][4][5] CW had an enhanced sweep efficiency compared to the other CO 2 -EOR methods such as CO 2 injection and water-alternating-gas (WAG) due to oil viscosity reduction and CW's ability to overcome the shielding effect. 6,12 The shielding prevents the CO 2 (free phase) from being in contact with the oil, but in the carbonated water, the CO 2 is dissolved in the water as an aqueous phase.…”

“…In the secondary flooding, a long contact time between the CLSW and oil is available, and the contact starts from the beginning of flooding. 3,13,10,4,18,8…”

“…Then, it will release the negative carboxylic oil component. This is because the negatively charged sulfate ion is relatively strongly attracted to the carbonate rock surface compared to the carboxylic acids rendering the rock surface less oil-wet and allowing the oil to flow through the pore throats 4,31,32…”

“…5 The dissolution (if occurs) will result in a larger pores diameter, thus lower capillary pressure in those pores, which could enhance the microscopic sweep efficiency. 3,31 Kilybay et al 4 reported some noticeable PSD changes based on the cores' NMR studies. This change occurs in the micro and macro scale, where they noticed a reduction in the micropores refers to blockages of porosity due to deposition of sulfate scales or produced fines.…”

“…Original Research Article: Mechanistic study of the carbonated smart the formation. [3][4][5] One of those cooptimization methods is carbonated water (CW) injection, where the injected water is enriched with CO 2 at the surface and injected as one fluid. However, CW injection proved significant in the enhancement of the oil recovery and typical decrease in the residual oil saturation over the traditional seawater injection.…”