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Toward Reservoir-on-a-Chip: Rapid Performance Evaluation of Enhanced Oil Recovery Surfactants for Carbonate Reservoirs Using a Calcite-Coated Micromodel.

ABSTRACT: Enhanced oil recovery (EOR) plays a significant role in improving oil production. Tertiary EOR, including surfactant flooding, can potentially mobilize residual oil after water flooding. Prior to the field deployment, the surfactant performance must be evaluated using site-specific crude oil at reservoir conditions. Core flood experiments are common practice to evaluate surfactants for oil displacement efficiency using core samples. Core flood experiments, however, are expensive and time-consuming and do not allow for pore scale observations of fluid-fluid interactions. This work introduces the framework to evaluate the performance of EOR surfactants via a Reservoir-on-a-Chip approach, which uses microfluidic devices to mimic the oil reservoir. A unique feature of this study is the use of chemically modified micromodels such that the pore surfaces are representative of carbonate reservoir rock. To represent calcium carbonate reservoir pores, the inner channels of glass microfluidic devices were coated with thin layers of calcium carbonate nanocrystals and the surface was modified to exhibit oil-wet conditions through a crude oil aging process. During surfactant screening, oil and water phases were imaged by fluorescence microscopy to reveal the micro to macro scale mechanisms controlling surfactant-assisted oil recovery. The role of the interfacial tension (IFT) and wettability in the microfluidic device was simulated using a phase-field model and compared to laboratory results. We demonstrated the effect of low IFT at the oil-water interface and wettability alteration on surfactant-enhanced oil displacement efficiency; thus providing a time-efficient and low-cost strategy for quantitative and qualitative assessment. In addition, this framework is an effective method for pre-screening EOR surfactants for use in carbonate reservoirs prior to further core and field scale testing.

SUBMITTER: Yun W

PROVIDER: S-EPMC6972785 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Simple plugging of the high-permeability "thief zones" of oil reservoirs is the most plausible and also the most straightforwardly achievable approach to enhance sweep efficiency and oil recovery. Sporosarcina pasteurii is a representative microorganism with the ability to precipitate calcium carbonate (CaCO3) via enzymatic hydrolysis of urea in the presence of calcium ions. Microbially induced calcium carbonate precipitation (MICP) can cement and seal the granular and fractured media and thus can be used as a potential microbial plugging agent for the high-permeability zones of oil reservoirs. The following investigated the microscopic characteristics of MICP plugging and its efficacy in permeability reduction. The columns of near-spherical silica sand and angular silica sand with three separate granularities (40/60, 60/80, and 80/120 mesh) were used as artificial rock cores representing distinct pore sizes and pore characteristics to investigate the efficacy and microprocess of MICP plugging with different biotreatment periods. The results indicated that permeability is reduced significantly after only short periods of biotreatment. After eight cycles of MICP treatments, the permeability for each type of cores dropped by 54-90% of individual initial permeabilities. The measured CaCO3 content indicated that the decreasing rate in permeability with the increasing CaCO3 content experiences three contrasting stages, namely, slow decline, speedy decline, and plateauing. X-ray diffraction indicated that most of the generated CaCO3 crystals occur as vaterite with only a small amount of calcite. Imaging by scanning electron microscopy further revealed the microprocess of MICP plugging. Microorganisms first concentrate on the pore wall to secrete CaCO3, forming a thin and large uniform layer of CaCO3. Then, some nucleation sites of CaCO3 crystals will experience further preferential growth, resulting in large, dominant crystals that act as a plugging agent within the pore space. Compared to extracellular polymeric substances, which are currently the primary microbial plugging agent used to enhance sweep efficiency of oil reservoirs, bio-CaCO3 appears more effective in plugging in terms of its morphology, size, and growth characteristics.

Project description:In this study, surfactants were used to enhance heavy oil-solid separation, and a detailed mechanism was explored by SARA (saturates, aromatics, resins, asphaltenes) analysis, element analysis, AFM measurement, and molecular dynamic simulation. Surfactants could effectively decrease oil/solid interaction force and then oil-solid separation would be enhanced. The oil-solid interactive force was in relation to surfactants concentration, pH value, asphaltene content, and salinity. The molecular dynamics simulation results show that the dissociation of saturated hydrocarbon, aromatic hydrocarbon, resin, and asphaltene (SARA) on carbonate minerals is gradually weakened for all surfactants. In the process of molecular dynamics simulation of surfactant stripping SARA, firstly, the surfactant molecules adsorb on the surface of SARA molecules. After that, the surfactant peels SARA molecules off the surface of calcite under the influence of molecular thermal motion. In this process, surfactant molecules will not be directly adsorbed on the surface of trace minerals. The results of energy/temperature balance indicated that saturates, aromatics and resins could remain stable when the molecular dynamics simulation time reached 2000 ps with the phenomenon that saturates, aromatics could liberate from minerals totally within 2000 ps. The molecular dynamics simulation of asphaltenes will not liberate from calcite surface within 6000 ps, meanwhile, they could not reach the energy balance/energy balance within 6000 ps. The functional groups of surfactant molecules would have interactions with the SARA functional group, resulting in different dissociation effects of SARA. The results of molecular dynamics simulation are consistent with the experiment results. The separation effect of saturated hydrocarbon, aromatic hydrocarbon, resin, and asphaltene in five kinds of surfactants were different. The molecular dynamic simulation results were in accordance with the SARA analysis.

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Toward Reservoir-on-a-Chip: Rapid Performance Evaluation of Enhanced Oil Recovery Surfactants for Carbonate Reservoirs Using a Calcite-Coated Micromodel.

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