Hybrid EOR Technology: Carbonated Water and Smart Water Improved Recovery in Oil Wet Carbonate Formation

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 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.

Experimental investigation of smart carbonated water injection method in carbonates

“…Although Karoon river has the lowest salinity among all water sources for preparing CW, it has the lowest RF(54%) due to the inconsistency of brine ions with the porous media. The increase in oil recovery by injection of SCW also has been observed in Kilibay et al .’s work as ions concentration has changed in injected carbonated brine.…”

“…pH investigation is a key point in combined SCW method to find out how much acidic the environment becomes as stated by Kilibay et al . They used hydrochloric acid at pressure of 350 psi instead of CW preparation due to the lack of equipment for providing acidic environment.…”

“…In addition, the works considered the combined method and only investigate one or two mechanisms or the conditions of experiments are limited, for example, Mohammadi et al . only measured IFT in smart carbonated water (SCW) using the pendant drop method without any dynamic core flooding, or Kilibay et al . dissolved CO 2 in brine at a pressure of 350 psi, which is low compared to reservoirs pressure, and due to this limitation they used hydrochloric acid for providing acidic environment instead of CW preparation.…”

Enhanced Wettability Modification and CO2 Solubility Effect by Carbonated Low Salinity Water Injection in Carbonate Reservoirs

“…They selected smart water as the sulfate ion-enriched brine through surface charge evaluation, rather than diluted seawater. However, only one of the three coreflooding experiments showed enhanced oil production, while the last two experiments showed negligible oil production [14]. Moreover, this approach did not account for any synergetic effects between smart water and carbonated brine.…”

“…Since both methods are waterflooding-based EOR processes, it is relatively straightforward to combine CWI with LSWI. Recently, Kilybay et al [14] have performed such a study in which they evaluated carbonated smart water flooding. They selected smart water as the sulfate ion-enriched brine through surface charge evaluation, rather than diluted seawater.…”